On-board diagnostics
   HOME

TheInfoList



OR:

On-board diagnostics (OBD) is a term referring to a vehicle's self-diagnostic and reporting capability. In the United States, this capability is a requirement to comply with federal emissions standards to detect failures that may increase the vehicle tailpipe emissions to more than 150% of the standard to which it was originally certified. OBD systems give the vehicle owner or repair technician access to the status of the various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s versions of onboard vehicle computers. Early versions of OBD would simply illuminate a tell-tale light if a problem was detected, but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide
real-time data Real-time data (RTD) is information that is delivered immediately after collection. There is no delay in the timeliness of the information provided. Real-time data is often used for navigation or tracking. Such data is usually data processing, proc ...
and diagnostic trouble codes which allow malfunctions within the vehicle to be rapidly identified.


History

* 1968:
Volkswagen Volkswagen (VW; )English: , . is a German automotive industry, automobile manufacturer based in Wolfsburg, Lower Saxony, Germany. Established in 1937 by German Labour Front, The German Labour Front, it was revitalized into the global brand it ...
introduces the first on-board computer system, in their fuel-injected Type 3 models. This system is entirely analog with no diagnostic capabilities. * 1975: Bosch and Bendix EFI systems are adopted by major automotive manufacturers to improve tailpipe (exhaust) emissions. These systems are also analog, though some provide rudimentary diagnostic capability through factory tools, such as the Kent Moore J-25400, compatible with the Datsun 280Z, and the Cadillac Seville. * 1980:
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
introduces the first data link on their 1980 Cadillac Eldorado and Seville models. Diagnostic Trouble Codes (DTCs) are displayed through the electronic climate control system's digital readout when in diagnostic mode. * 1981:
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
introduced its "Computer Command Control" system on all US passenger vehicles for model year 1981. Included in this system is a proprietary 5-pin ALDL that interfaces with the Engine Control Module (ECM) to initiate a diagnostic request and provide a serial data stream. The protocol communicates at 160 baud with
Pulse-width modulation Pulse-width modulation (PWM), also known as pulse-duration modulation (PDM) or pulse-length modulation (PLM), is any method of representing a signal as a rectangular wave with a varying duty cycle (and for some methods also a varying peri ...
(PWM) signaling and monitors all engine management functions. It reports real-time sensor data, component overrides, and Diagnostic Trouble Codes. The specification for this link is as defined by GM's Emissions Control System Project Center document XDE-5024B. * 1982: RCA defines an analog STE/ICE (simplified test equipment for internal combustion engines) vehicle diagnostic standard used in the CUCV, M60 tank and other military vehicles of the era for the US Army. * 1986:
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
introduces an upgraded version of the ALDL protocol, which communicates at 8192 baud with half-duplex UART signaling on some models. * 1988: The California Air Resources Board (CARB) requires that all new vehicles sold in
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
from 1988 onward have some basic OBD capability (such as detecting problems with fuel metering and
Exhaust gas recirculation In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide () emissions reduction technique used in petrol engine, petrol/gasoline, diesel engines and some hydrogen internal combustion engine vehicle, hydrogen engines. ...
.) These requirements are generally referred to as "OBD-I", though this name is a
retronym A retronym is a newer name for something that differentiates it from something else that is newer, similar, or seen in everyday life; thus, avoiding confusion between the two. Etymology The term ''retronym'', a neologism composed of the combi ...
applied after the introduction of OBD-II. The data link connector and its position are not standardized, nor is the data protocol. The Society of Automotive Engineers (SAE) recommends a standardized diagnostic connector and set of diagnostic test signals. * ~1994: Motivated by a desire for a state-wide emissions testing program, the CARB issues the OBD-II specification and mandates that it be adopted for all cars sold in California starting in model year 1996 (see CCR Title 13 Section 1968.1 and 40 CFR Part 86 Section 86.094). The DTCs and connectors suggested by the SAE are incorporated into this specification. * 1996: The OBD-II specification is made mandatory for all passenger cars and petrol-powered light trucks with a gross vehicle weight rating less than in the United States. The OBD-II specification is also made mandatory for all petrol-powered vehicles with California emissions with a gross vehicle weight rating up to . * 1997: The OBD-II specification is made mandatory for California emissions diesel-engined vehicles with a gross vehicle weight rating up to . * 2001: The
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
makes EOBD mandatory for all petrol vehicles sold in the European Union, starting in MY2001 (see European emission standards Directive 98/69/EC). * 2004: The
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
makes EOBD mandatory for all diesel vehicles sold in the European Union. All petrol-powered vehicles in the United States with a gross vehicle weight rating of up to are required to have OBD-II. * 2006: All vehicles manufactured in
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
and
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
are required to be OBD-II compliant after January 1, 2006. All vehicles in the United States of gross vehicle weight rating and under are required to have OBD-II. * 2007: All California emissions vehicles over gross vehicle weight rating are required to support EMD/EMD+ or OBD-II. * 2008: All cars sold in the United States are required to use the ISO 15765-4 signaling standard (a variant of the
Controller Area Network A controller area network bus (CAN bus) is a vehicle bus standard designed to enable efficient communication primarily between electronic control units (ECUs). Originally developed to reduce the complexity and cost of electrical wiring in aut ...
(CAN) bus). * 2008: Certain light vehicles in China are required by the Environmental Protection Administration Office to implement OBD (standard GB18352) by July 1, 2008. Some regional exemptions may apply. * 2010: Start of required phase-in of the OBD-II specification to all vehicles with a gross vehicle weight rating of and above, this was completed by the 2013 model year. Vehicles that did not have OBD-II during this time period were required to have EMD/EMD+.


Standard interfaces


ALDL

GM's ALDL (Assembly Line Diagnostic Link) is sometimes referred to as a predecessor to, or a manufacturer's proprietary version of, an OBD-I diagnostic starting in 1981. This interface was made in different varieties and changed with power train control modules (aka PCM, ECM, ECU). Different versions had slight differences in pin-outs and baud rates. Earlier versions used a 160 baud rate, while later versions went up to 8192 baud and used bi-directional communications to the PCM.


OBD-I

The regulatory intent of OBD-I was to encourage auto manufacturers to design reliable emission control systems that remain effective for the vehicle's "useful life". The hope was that by forcing annual emissions testing for
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
starting in 1988, and denying registration to vehicles that did not pass, drivers would tend to purchase vehicles that would more reliably pass the test. OBD-I was largely unsuccessful, as the means of reporting emissions-specific diagnostic information was not standardized. Technical difficulties with obtaining standardized and reliable emissions information from all vehicles led to an inability to implement the annual testing program effectively. The Diagnostic Trouble Codes (DTC's) of OBD-I vehicles can usually be found without an expensive scan tool. Each manufacturer used their own Diagnostic Link Connector (DLC), DLC location, DTC definitions, and procedure to read the DTC's from the vehicle. DTC's from OBD-I cars are often read through the blinking patterns of the 'Check Engine Light' (CEL) or 'Service Engine Soon' (SES) light. By connecting certain pins of the diagnostic connector, the 'Check Engine' light will blink out a two-digit number that corresponds to a specific error condition. The DTC's of some OBD-I cars are interpreted in different ways, however. Cadillac fuel-injected vehicles are equipped with actual ''onboard'' diagnostics, providing trouble codes, actuator tests and sensor data through the new digital Electronic Climate Control display. Holding down 'Off' and 'Warmer' for several seconds activates the diagnostic mode without the need for an external scan tool. Some Honda engine computers are equipped with LEDs that light up in a specific pattern to indicate the DTC. General Motors, some 1989–1995 Ford vehicles (DCL), and some 1989–1995 Toyota/Lexus vehicles have a live sensor data stream available; however, many other OBD-I equipped vehicles do not. OBD-I vehicles have fewer DTC's available than OBD-II equipped vehicles.


OBD-1.5

OBD 1.5 refers to a partial implementation of OBD-II which
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
used on some vehicles in 1994, 1995 & 1996 (GM did not use the term OBD 1.5 in the documentation for these vehicles — they simply had an OBD and an OBD-II section in the service manual). For example, the 1994–1995 model year Corvettes have one post-catalyst oxygen sensor (although they have two
catalytic converter A catalytic converter part is an vehicle emissions control, exhaust emission control device which converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalysis, catalyzing a redox ...
s), and have a subset of the OBD-II codes implemented. This hybrid system was present on GM B-body cars (the Chevrolet Caprice, Impala, and Buick Roadmaster) for 1994–1995 model years, H-body cars for 1994–1995, W-body cars (Buick Regal, Chevrolet Lumina) for 1995 only, Chevrolet Monte Carlo (1995 only), Pontiac Grand Prix, Oldsmobile Cutlass Supreme (for 1994–1995), L-body (Chevrolet Beretta/Corsica) for 1994–1995, Y-body (Chevrolet Corvette) for 1994–1995, on the F-body (Chevrolet Camaro and Pontiac Firebird) for 1995 and on the J-Body (Chevrolet Cavalier and Pontiac Sunfire) and N-Body (Buick Skylark, Oldsmobile Achieva, Pontiac Grand Am) for 1995 and 1996 and also for North American delivered 1994–1995 Saab vehicles with the naturally aspirated 2.3. The pinout for the ALDL connection on these cars is as follows: For ALDL connections, pin 9 is the data stream, pins 4 and 5 are ground, and pin 16 is the battery voltage. An OBD 1.5 compatible scan tool is required to read codes generated by OBD 1.5. Additional vehicle-specific diagnostic and control circuits are also available on this connector. For instance, on the Corvette there are interfaces for the Class 2 serial data stream from the PCM, the CCM diagnostic terminal, the radio data stream, the airbag system, the selective ride control system, the low tire pressure warning system, and the passive keyless entry system. An OBD 1.5 has also been used in the Ford Scorpio since 95.


OBD-II

OBD-II is an improvement over OBD-I in both capability and standardization. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each. There is a pin in the connector that provides power for the scan tool from the vehicle battery, which eliminates the need to connect a scan tool to a power source separately. However, some technicians might still connect the scan tool to an auxiliary power source to protect data in the unusual event that a vehicle experiences a loss of electrical power due to a malfunction. Finally, the OBD-II standard provides an extensible list of DTCs. As a result of this standardization, a single device can query the on-board computer(s) in any vehicle. This OBD-II came in two models OBD-IIA and OBD-IIB. OBD-II standardization was prompted by emissions requirements, and though only emission-related codes and data are required to be transmitted through it, most manufacturers have made the OBD-II Data Link Connector the only one in the vehicle through which all systems are diagnosed and programmed. OBD-II Diagnostic Trouble Codes are 4-digit, preceded by a letter: P for powertrain (engine and transmission), B for body, C for chassis, and U for network.


OBD-II diagnostic connector

The OBD-II specification provides for a standardized hardware interface — the female 16-pin (2x8) J1962 connector, where type A is used for 12-volt vehicles and type B for 24-volt vehicles. Unlike the OBD-I connector, which was sometimes found under the bonnet of the vehicle, the OBD-II connector is required to be within of the steering wheel (unless an exemption is applied for by the manufacturer, in which case it is still somewhere within reach of the driver). SAE J1962 defines the pinout of the connector as: The assignment of unspecified pins is left to the vehicle manufacturer's discretion.


EOBD

The European on-board diagnostics (EOBD) regulations are the European equivalent of OBD-II, and apply to all passenger cars of category M1 (with no more than 8 passenger seats and a Gross Vehicle Weight rating of or less) first registered within EU member states since January 1, 2001 for
petrol Gasoline (North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When formul ...
-engined cars and since January 1, 2004 for diesel engined cars. For newly introduced models, the regulation dates applied a year earlier – January 1, 2000 for petrol and January 1, 2003, for diesel.
For passenger cars with a Gross Vehicle Weight rating of greater than 2500 kg and for light commercial vehicles, the regulation dates applied from January 1, 2002, for petrol models, and January 1, 2007, for diesel models. The technical implementation of EOBD is essentially the same as OBD-II, with the same SAE J1962 diagnostic link connector and signal protocols being used. With Euro V and Euro VI emission standards, EOBD emission thresholds are lower than previous Euro III and IV.


EOBD fault codes

Each of the EOBD fault codes consists of five characters: a letter, followed by four numbers. The letter refers to the system being interrogated e.g. Pxxxx would refer to the powertrain system. The next character would be a 0 if complies to the EOBD standard. So it should look like P0xxx. The next character would refer to the sub system. *P00xx – Fuel and Air Metering and Auxiliary Emission Controls. *P01xx – Fuel and Air Metering. *P02xx – Fuel and Air Metering (Injector Circuit). *P03xx – Ignition System or Misfire. *P04xx – Auxiliary Emissions Controls. *P05xx – Vehicle Speed Controls and Idle Control System. *P06xx – Computer Output Circuit. *P07xx – Transmission. *P08xx – Transmission. The following two characters would refer to the individual fault within each subsystem.


EOBD2

The term "EOBD2" is marketing speak used by some vehicle manufacturers to refer to manufacturer-specific features that are not actually part of the OBD or EOBD standard. In this case "E" stands for Enhanced.


JOBD

JOBD is a version of OBD-II for vehicles sold in Japan.


ADR 79/01 & 79/02 (Australian OBD standard)

The ADR 79/01 Vehicle Standard (Australian Design Rule 79/01 – Emission Control for Light Vehicles, 2005) is the Australian equivalent of OBD-II. It applies to all vehicles of category M1 and N1 with a Gross Vehicle Weight rating of or less, registered from new within Australia and produced since January 1, 2006 for
petrol Gasoline (North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When formul ...
-engined cars and since January 1, 2007 for diesel-engined cars. For newly introduced models, the regulation dates applied a year earlier – January 1, 2005 for petrol and January 1, 2006, for diesel. The ADR 79/01 standard was supplemented by the ADR 79/02 standard which imposed tighter emissions restrictions, applicable to all vehicles of class M1 and N1 with a Gross Vehicle Weight rating of 3500 kg or less, from July 1, 2008, for new models, July 1, 2010, for all models. The technical implementation of this standard is essentially the same as OBD-II, with the same SAE J1962 diagnostic link connector and signal protocols being used.


EMD/EMD+

In North America, EMD and EMD+ are on-board diagnostic systems that were used on vehicles with a gross vehicle weight rating of or more between the 2007 and 2012 model years if those vehicles did not already implement OBD-II. EMD was used on California emissions vehicles between model years 2007 and 2009 that did not already have OBD-II. EMD was required to monitor fuel delivery, exhaust gas recirculation, the
diesel particulate filter A diesel particulate filter (DPF) is a device designed to remove diesel exhaust#Particulates, diesel particulate matter or soot from the exhaust gas of a diesel engine.Tom Nash (May 2003) "Diesels: The Smoke is clearing", ''Motor '' Vol.199 No. ...
(on diesel engines), and emissions-related powertrain control module inputs and outputs for circuit continuity, data rationality, and output functionality. EMD+ was used on model year 2010-2012 California and Federal petrol-engined vehicles with a gross vehicle weight rating of over , it added the ability to monitor nitrogen oxide catalyst performance. EMD and EMD+ are similar to OBD-I in logic but use the same SAE J1962 data connector and CAN bus as OBD-II systems.


OBD-II signal protocols

Five signaling protocols are permitted with the OBD-II interface. Most vehicles implement only one of the protocols. It is often possible to deduce the protocol used based on which pins are present on the J1962 connector: * SAE J1850 PWM (
pulse-width modulation Pulse-width modulation (PWM), also known as pulse-duration modulation (PDM) or pulse-length modulation (PLM), is any method of representing a signal as a rectangular wave with a varying duty cycle (and for some methods also a varying peri ...
— 41.6 kB/sec, standard of the
Ford Motor Company Ford Motor Company (commonly known as Ford) is an American multinational corporation, multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. T ...
) **pin 2: Bus+ **pin 10: Bus– **High voltage is +5 V **Message length is restricted to 12 bytes, including CRC **Employs a multi-master arbitration scheme called ' Carrier Sense Multiple Access with Non-Destructive Arbitration' (CSMA/NDA) * SAE J1850 VPW ( variable pulse width — 10.4/41.6 kB/sec, standard of
General Motors General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...
) **pin 2: Bus+ **Bus idles low **High voltage is +7 V **Decision point is +3.5 V **Message length is restricted to 12 bytes, including CRC **Employs CSMA/NDA * ISO 9141-2 This protocol has an asynchronous serial data rate of 10.4 kbit/s. It is somewhat similar to
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...
; however, the signal levels are different, and communications happen on a single, bidirectional line without additional handshake signals. ISO 9141-2 is primarily used in Chrysler, European, and Asian vehicles. **pin 7: K-line **pin 15: L-line (optional) **UART signaling **K-line idles high, with a 510 ohm resistor to Vbatt **The active/dominant state is driven low with an open-collector driver **Message length is max 260 Bytes ( payload field max is 255 Bytes) * ISO 14230 KWP2000 ( Keyword Protocol 2000) **pin 7: K-line **pin 15: L-line (optional) **Physical layer identical to ISO 9141-2 **Data rate 1.2 to 10.4 kBaud **Message may contain up to 255 bytes in the data field * ISO 15765 CAN (250 kbit/s or 500 kbit/s). The CAN protocol was developed by Bosch for automotive and industrial control. Unlike other OBD protocols, variants are widely used outside of the automotive industry. While it did not meet the OBD-II requirements for U.S. vehicles prior to 2003, as of 2008 all vehicles sold in the US are required to implement CAN as one of their signaling protocols. **pin 6: CAN High **pin 14: CAN Low All OBD-II pinouts use the same connector, but different pins are used with the exception of pin 4 (battery ground) and pin 16 (battery positive).


OBD-II diagnostic data available

OBD-II provides access to data from the
engine control unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...
(ECU) and offers a valuable source of information when troubleshooting problems inside a vehicle. The SAE J1979 standard defines a method for requesting various diagnostic data and a list of standard parameters that might be available from the ECU. The various available parameters are addressed by "parameter identification numbers" or PIDs which are defined in J1979. For a list of basic PIDs, their definitions, and the formula to convert raw OBD-II output to meaningful diagnostic units, see OBD-II PIDs. Manufacturers are not required to implement all PIDs listed in J1979 and they are allowed to include proprietary PIDs that are not listed. The PID request and data retrieval system gives access to real time performance data as well as flagged DTCs. For a list of generic OBD-II DTCs suggested by the SAE, see Table of OBD-II Codes. Individual manufacturers often enhance the OBD-II code set with additional proprietary DTCs.


Mode of operation/OBD services

Here is a basic introduction to the OBD
communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer science), sem ...
according to ISO 15031. In SAE J1979 these "modes" were renamed to "services", starting in 2003. * Service / Mode $01 shows current sensor live data from PIDs ("Parameter IDs"). See OBD-II PIDs#Service_01 for an extensive list. * Service / Mode $02 makes Freeze Frame data accessible via the same PIDs. See OBD-II PIDs#Service_02 for a list. * Service / Mode $03 lists the emission-related "confirmed" diagnostic trouble codes stored. It either displays numeric, 4 digit codes identifying the faults or maps them to a letter (P, B, U, C) plus 4 digits. See #OBD-II_diagnostic_trouble_codes. * Service / Mode $04 is used to clear emission-related diagnostic information. This includes clearing the stored pending/confirmed DTCs and Freeze Frame data. * Service / Mode $05 displays the oxygen sensor monitor screen and the test results gathered about the oxygen sensor. There are ten numbers available for diagnostics: ** $01 Rich-to-Lean O2 sensor threshold voltage ** $02 Lean-to-Rich O2 sensor threshold voltage ** $03 Low sensor voltage threshold for switch time measurement ** $04 High sensor voltage threshold for switch time measurement ** $05 Rich-to-Lean switch time in ms ** $06 Lean-to Rich switch time in ms ** $07 Minimum voltage for test ** $08 Maximum voltage for test ** $09 Time between voltage transitions in ms ** See OBD-II PIDs#Service_05 for a list. * Service / Mode $06 is a Request for On-Board Monitoring Test Results for Continuously and Non-Continuously Monitored System. There are typically a minimum value, a maximum value, and a current value for each non-continuous monitor. * Service / Mode $07 is a Request for emission-related diagnostic trouble codes detected during current or last completed driving cycle. It enables the external test equipment to obtain "pending" diagnostic trouble codes detected during current or last completed driving cycle for emission-related components/systems. This is used by service technicians after a vehicle repair, and after clearing diagnostic information to see test results after a single driving cycle to determine if the repair has fixed the problem. See #OBD-II_diagnostic_trouble_codes. * Service / Mode $08 could enable the off-board test device to control the operation of an on-board system, test, or component. * Service / Mode $09 is used to retrieve vehicle information. Among others, the following information is available: ** VIN (
Vehicle Identification Number A vehicle identification number (VIN; also called a chassis number or frame number) is a unique code, including a serial number, used by the automotive industry to identify individual motor vehicles, towed vehicles, motorcycles, scooters a ...
): Vehicle ID ** CALID (Calibration Identification): ID for the software installed on the ECU ** CVN (Calibration Verification Number): Number used to verify the integrity of the vehicle software. The manufacturer is responsible for determining the method of calculating CVN(s), e.g. using checksum. ** In-use performance counters *** Petrol engine : Catalyst, Primary oxygen sensor, Evaporating system, EGR system, VVT system, Secondary air system, and Secondary oxygen sensor *** Diesel engine : NMHC catalyst, NOx reduction catalyst, NOx absorber Particulate matter filter, Exhaust gas sensor, EGR system, VVT system, Boost pressure control, Fuel system. ** See OBD-II PIDs#Service_09 for an extensive list. * Service / Mode $0A lists emission-related "permanent" diagnostic trouble codes stored. As per CARB, any diagnostic trouble codes that is commanding MIL on and stored into non-volatile memory shall be logged as a permanent fault code. See #OBD-II_diagnostic_trouble_codes.


Applications

Various tools are available that plug into the OBD connector to access OBD functions. These range from simple generic consumer level tools to highly sophisticated OEM dealership tools to vehicle telematic devices.


Hand-held scan tools

A range of rugged hand-held scan tools is available. * Simple fault code readers/reset tools are mostly aimed at the consumer level. * Professional hand-held scan tools may possess more advanced functions ** Access more advanced diagnostics ** Set manufacturer- or vehicle-specific ECU parameters ** Access and control other control units, such as air bag or ABS ** Real-time monitoring or graphing of engine parameters to facilitate diagnosis or tuning


Mobile device-based tools and analysis

Mobile device applications allow mobile devices such as cell phones and tablets to display and manipulate the OBD-II data accessed via
USB Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...
adaptor cables or
Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is li ...
adapters plugged into the car's OBD II connector. Newer devices on the market are equipped with GPS sensors and the ability to transmit vehicle location and diagnostics data over a cellular network. Modern OBD-II devices can therefore nowadays be used to for example locate vehicles, monitor driving behavior in addition to reading Diagnostics Trouble Codes (DTC). Even more advanced devices allow users to reset engine DTC codes, effectively turning off engine lights in the dashboard; however, resetting the codes does not address the underlying issues and can in worst-case scenarios even lead to engine breakage where the source issue is serious and left unattended for long periods.


OBD-II Software

An OBD-II software package when installed in a computer (
Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
, Mac, or
Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...
) can help diagnose the onboard system, read and erase DTCs, turn off MIL, show real-time data, and measure vehicle fuel economy. To use OBD-II software, one needs to have an OBD-II adapter (commonly using
Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is li ...
,
Wi-Fi Wi-Fi () is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital devices to exchange data by ...
or
USB Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...
) plugged in the OBD-II port to enable the vehicle to connect with the computer where the software is installed.


PC-based scan tools and analysis platforms

A PC-based OBD analysis tool that converts the OBD-II signals to serial data (USB or serial port) standard to PCs or Macs. The software then decodes the received data to a visual display. Many popular interfaces are based on the ELM327 or STN OBD Interpreter ICs, both of which read all five generic OBD-II protocols. Some adapters now use the J2534 API allowing them to access OBD-II Protocols for both cars and trucks. In addition to the functions of a hand-held scan tool, the PC-based tools generally offer: * Large storage capacity for data logging and other functions * Higher resolution screen than handheld tools * The ability to use multiple software programs adding flexibility * The identification and clearance of fault code * Data shown by intuitive graphs and charts The extent that a PC tool may access manufacturer or vehicle-specific ECU diagnostics varies between software products as it does between hand-held scanners.


Data loggers

Data logger A data logger (also datalogger or data recorder) is an electronic device that records data over time or about location either with a built-in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they a ...
s are designed to capture vehicle data while the vehicle is in normal operation, for later analysis. Data logging uses include: * Engine and vehicle monitoring under normal operation, for diagnosis or tuning. * Some US auto insurance companies offer reduced premiums if OBD-II vehicle data loggers or cameras are installed – and if the driver's behaviour meets requirements. This is a form of auto insurance risk selection * Monitoring of driver behaviour by fleet vehicle operators. Analysis of vehicle black box data may be performed periodically, automatically transmitted wirelessly to a third party or retrieved for forensic analysis after an event such as an accident, traffic infringement or mechanical fault.


Emission testing

In the United States, many states now use OBD-II testing instead of tailpipe testing in OBD-II compliant vehicles (1996 and newer). Since OBD-II stores trouble codes for emissions equipment, the testing computer can query the vehicle's onboard computer and verify there are no emission related trouble codes and that the vehicle is in compliance with emission standards for the model year it was manufactured. In the Netherlands, 2006 and later vehicles get a yearly EOBD emission check.


Driver's supplementary vehicle instrumentation

Driver's supplementary vehicle instrumentation is instrumentation installed in a vehicle in addition to that provided by the vehicle manufacturer and intended for display to the driver during normal operation. This is opposed to scanners used primarily for active fault diagnosis, tuning, or hidden data logging. Auto enthusiasts have traditionally installed additional gauges such as manifold vacuum, battery current etc. The OBD standard interface has enabled a new generation of enthusiast instrumentation accessing the full range of vehicle data used for diagnostics, and derived data such as instantaneous fuel economy. Instrumentation may take the form of dedicated
trip computer A trip computer is a computer fitted to some cars; most modern trip computers record, calculate, and display the distance travelled, the average speed, the average fuel consumption, and real-time fuel consumption. The first, mechanical trip ...
s, carputer or interfaces to PDAs, smartphones, or a
Garmin Garmin Ltd. is an American multinational technology company based in Olathe, Kansas. The company designs, develops, manufactures, markets, and distributes GPS-enabled products and other navigation, communication, sensor-based, and information ...
navigation unit. As a carputer is essentially a PC, the same software could be loaded as for PC-based scan tools and vice versa, so the distinction is only in the reason for use of the software. These enthusiast systems may also include some functionality similar to the other scan tools.


Vehicle telematics

OBD II information is commonly used by vehicle telematics devices that perform fleet tracking, monitor fuel efficiency, prevent unsafe driving, as well as for remote diagnostics and by pay-as-you-drive insurance. Although originally not intended for the above purposes, commonly supported OBD II data such as vehicle speed, RPM, and fuel level allow GPS-based fleet tracking devices to monitor vehicle idling times, speeding, and over-revving. By monitoring OBD II DTCs a company can know immediately if one of its vehicles has an engine problem and by interpreting the code the nature of the problem. It can be used to detect reckless driving in real time based on the sensor data provided through the OBD port. This detection is done by adding a complex events processor (CEP) to the backend and on the client's interface. OBD II is also monitored to block mobile phones when driving and to record trip data for insurance purposes.


OBD-II diagnostic trouble codes

OBD-II diagnostic trouble codes ( DTCs) are five characters long, with the first letter indicating a category, and the remaining four being a
hexadecimal Hexadecimal (also known as base-16 or simply hex) is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of sixteen. Unlike the decimal system representing numbers using ten symbo ...
number.ELM327DSL.pdf, p. 36. The first character, representing category can only be one of the following four letters, given here with their associated meanings. (This restriction in number is due to how only two bits of memory are used to indicate the category when DTCs are stored and transmitted). * P – Powertrain (engine, transmission and ignition) * C – Chassis (includes ABS and brake fluid) * B – Body (includes air conditioning and airbag) * U – Network (wiring bus) The second character is a number in the range of 0–3. (This restriction is again due to memory storage limitations). * 0 – Indicates a generic (SAE defined) code * 1 – Indicates a manufacturer-specific (OEM) code * 2 – Category dependent: ** For the 'P' category this indicates a generic (SAE defined) code ** For other categories indicates a manufacturer-specific (OEM) code * 3 – Category dependent: ** For the 'P' category this is indicates a code that has been 'jointly' defined ** For other categories this has been reserved for future use The third character may denote a particular vehicle system that the fault relates to. * 0 – Fuel and air metering and auxiliary emission controls * 1 – Fuel and air metering * 2 – Fuel and air metering (injector circuit) * 3 – Ignition systems or misfires * 4 – Auxiliary emission controls * 5 – Vehicle speed control and idle control systems * 6 – Computer and output circuit * 7 – Transmission * 8 – Transmission * A-F – Hybrid Trouble Codes Finally the fourth and fifth characters define the exact problem detected.


Standards documents


SAE standards documents on OBD-II

*J1962 – Defines the physical connector used for the OBD-II interface. *J1850 – Defines a serial data protocol. There are 2 variants: 10.4 kbit/s (single wire, VPW) and 41.6 kbit/s (2 wire, PWM). Mainly used by US manufacturers, also known as PCI (Chrysler, 10.4K), Class 2 (GM, 10.4K), and SCP (Ford, 41.6K) *J1978 – Defines minimal operating standards for OBD-II scan tools *J1979 – Defines standards for diagnostic test modes *J2012 – Defines standards trouble codes and definitions. *J2178-1 – Defines standards for network message header formats and physical address assignments *J2178-2 – Gives data parameter definitions *J2178-3 – Defines standards for network message frame IDs for single byte headers *J2178-4 – Defines standards for network messages with three byte headers *J2284-3 – Defines 500K CAN physical and
data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...
*J2411 – Describes the GMLAN (Single-Wire CAN) protocol, used in newer GM vehicles. Often accessible on the OBD connector as PIN 1 on newer GM vehicles


SAE standards documents on HD (Heavy Duty) OBD

* J1939 – Defines a data protocol for heavy duty commercial vehicles


ISO standards

*ISO 9141: Road vehicles – Diagnostic systems.
International Organization for Standardization The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. M ...
, 1989. **Part 1: Requirements for interchange of digital information **Part 2: CARB requirements for interchange of digital information **Part 3: Verification of the communication between vehicle and OBD II scan tool *ISO 11898: Road vehicles – Controller area network (CAN). International Organization for Standardization, 2003. **Part 1: Data link layer and physical signalling **Part 2: High-speed medium access unit **Part 3: Low-speed, fault-tolerant, medium-dependent interface **Part 4: Time-triggered communication *ISO 14230: Road vehicles – Diagnostic systems – Keyword Protocol 2000, International Organization for Standardization, 1999. **Part 1: Physical layer **Part 2: Data link layer **Part 3: Application layer **Part 4: Requirements for emission-related systems *ISO 15031: Communication between vehicle and external equipment for emissions-related diagnostics, International Organization for Standardization, 2010. **Part 1: General information and use case definition **Part 2: Guidance on terms, definitions, abbreviations and acronyms **Part 3: Diagnostic connector and related electrical circuits, specification and use **Part 4: External test equipment **Part 5: Emissions-related diagnostic services **Part 6: Diagnostic trouble code definitions **Part 7: Data link security *ISO 15765: Road vehicles – Diagnostics on Controller Area Networks (CAN). International Organization for Standardization, 2004. **Part 1: General information **Part 2: Network layer services ISO 15765-2 **Part 3: Implementation of unified diagnostic services ( UDS on CAN) **Part 4: Requirements for emissions-related systems


Security issues

Researchers at the
University of Washington The University of Washington (UW and informally U-Dub or U Dub) is a public research university in Seattle, Washington, United States. Founded in 1861, the University of Washington is one of the oldest universities on the West Coast of the Uni ...
and
University of California The University of California (UC) is a public university, public Land-grant university, land-grant research university, research university system in the U.S. state of California. Headquartered in Oakland, California, Oakland, the system is co ...
examined the security around OBD and found that they were able to gain control over many vehicle components via the interface. Furthermore, they were able to upload new
firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...
into the
engine control unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...
s. Their conclusion is that vehicle
embedded system An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is e ...
s are not designed with security in mind. There have been reports of thieves using specialist OBD reprogramming devices to enable them to steal cars without the use of a key. The primary causes of this vulnerability lie in the tendency for vehicle manufacturers to extend the bus for purposes other than those for which it was designed, and the lack of
authentication Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proving an Logical assertion, assertion, such as the Digital identity, identity of a computer system user. In contrast with iden ...
and
authorization Authorization or authorisation (see American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), in information security, computer security and identity management, IAM (Identity and Access Managemen ...
in the OBD specifications, which instead rely largely on security through obscurity.


See also

* OBD-II PIDs ("Parameter IDs") * Unified Diagnostic Services *
Engine control unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...
* Immobiliser


References

;Notes * Birnbaum, Ralph and Truglia, Jerry. ''Getting to Know OBD II''. New York, 2000. . * SAE International. ''On-Board Diagnostics for Light and Medium Duty Vehicles Standards Manual''. Pennsylvania, 2003. .


External links


Directive 98/69/EC of the European Parliament and of the Council of 13 October 1998.

National OBD Clearing House
Center for Automotive Science and Technology at Weber State University
United States Environmental Protection Agency
OBD information for repair technicians, vehicle owners, and manufacturers {{DEFAULTSORT:On-Board Diagnostics Automotive technologies Industrial computing Vehicle security systems