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On-board diagnostics

On-board diagnostics

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Encyclopedia
On-Board Diagnostics, or OBD, in an automotive context, is a generic term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since the introduction in the early 1980s of on-board vehicle computers, which made OBD possible. Early instances of OBD would simply illuminate a malfunction indicator light, or MIL, 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 in addition to a standardized series of diagnostic trouble codes, or DTCs, which allow one to rapidly identify and remedy malfunctions within the vehicle.

History

  • 1969: Volkswagen
    Volkswagen
    Volkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is...

     introduces the first on-board computer system with scanning capability, in their fuel-injected Type 3
    Volkswagen Type 3
    The Volkswagen Type 3 was a range of small cars from German manufacturer Volkswagen , introduced at the 1961 Frankfurt Motor Show, Internationale Automobil-Ausstellung ....

     models.
  • 1975: Datsun 280Z On-board computers begin appearing on consumer vehicles, largely motivated by their need for real-time tuning of fuel injection
    Fuel injection
    Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

     systems. Simple OBD implementations appear, though there is no standardization in what is monitored or how it is reported.
  • 1980: General Motors
    General Motors
    General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...

     implements a proprietary interface and protocol
    Communications protocol
    A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...

     for testing of the Engine Control Module (ECM) on the vehicle assembly line. The 'assembly line diagnostic link' (ALDL
    ALDL
    Assembly Line Diagnostic Link or ALDL was a proprietary on-board diagnostics system developed by General Motors prior to the standardization of OBD-I....

    ) protocol communicates at 160 baud
    Baud
    In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...

     with Pulse-width modulation
    Pulse-width modulation
    Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....

     (PWM) signaling and monitors very few vehicle systems. Implemented on California vehicles for the 1980 model year, and the rest of the United States in 1981, the ALDL was not intended for use outside the factory. The only available function for the owner is "Blinky Codes". By connecting pins A and B (with ignition key ON and engine OFF), the 'Check Engine Light' (CEL) blinks out a two-digit number that corresponds to a specific error condition. Cadillac (gasoline) fuel-injected vehicles, however, are equipped with actual on-board 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 need for an external scan-tool.
  • 1986: An upgraded version of the ALDL protocol appears which communicates at 8192 baud with half-duplex UART signaling. This protocol is defined in GM XDE-5024B.
  • 1988: The Society of Automotive Engineers (SAE) recommends a standardized diagnostic connector and set of diagnostic test signals.
  • 1991: The California Air Resources Board
    California Air Resources Board
    The California Air Resources Board, also known as CARB or ARB, is the "clean air agency" in the government of California. Established in 1967 in the Mulford-Carrell Act, combining the Bureau of Air Sanitation and the Motor Vehicle Pollution Control Board, CARB is a department within the...

     (CARB) requires that all new vehicles sold in California
    California
    California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

    in 1991 and newer vehicles have some basic OBD capability. These requirements are generally referred to as "OBD-I", though this name is not applied until
    Retronym
    A retronym is a type of neologism that provides a new name for an object or concept to differentiate the original form or version of it from a more recent form or version. The original name is most often augmented with an adjective to account for later developments of the object or concept itself...

     the introduction of OBD-II. The data link connector and its position are not standardized, nor is the data protocol.
  • ~1994: Motivated by a desire for a state-wide emissions testing
    Automobile emissions control
    Vehicle emissions control is the study and practice of reducing the motor vehicle emissions -- emissions produced by motor vehicles, especially internal combustion engines....

     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 connector suggested by the SAE are incorporated into this specification.
  • 1996: The OBD-II specification is made mandatory for all cars sold in the United States.
  • 2001: The European Union
    European Union
    The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

     makes EOBD mandatory for all gasoline (petrol) vehicles sold in the European Union, starting in MY2001 (see European emission standards
    European emission standards
    European emission standards define the acceptable limits for exhaust emissions of new vehicles sold in EU member states. The emission standards are defined in a series of European Union directives staging the progressive introduction of increasingly stringent standards.Currently, emissions of...

     Directive 98/69/EC http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1998L0069:19981228:EN:PDF).
  • 2008: All cars sold in the United States are required to use the ISO 15765-4 http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=33619&COMMID=&scopelist= signaling standard (a variant of the Controller Area Network
    Controller Area Network
    Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....

     (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: HDOBD (heavy duty) specification is made mandatory for selected commercial (non-passenger car) engines sold in the United States.

Standard interfaces


GM's ALDL
ALDL
Assembly Line Diagnostic Link or ALDL was a proprietary on-board diagnostics system developed by General Motors prior to the standardization of OBD-I....

 (Assembly Line Diagnostic Link) is sometimes referred as a predecessor to, or a manufacturer's proprietary version of, an OBD-I diagnostic. 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.

http://www.webpg.net/ALDLbareINST.pdf
http://www.techedge.com.au/vehicle/aldl160/160serial.htm
http://tunertools.com/vendorinfo/AKM_cables/GMALDLsoftware.asp
http://tunertools.com/vendorinfo/AKM_cables/AKM_electronics.asp
http://www.aldlcable.com/sc/details.asp?item=aldlobd1

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
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, 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.

OBD-1.5


OBD 1.5 refers to a partial implementation of OBD-II which General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...

 used on some vehicles in 1994 and 1995. (GM did not use the term OBD 1.5 in the documentation for these vehicles - they simply have an OBD and an OBD-II section in the service manual.)

For example, the 94-95 Corvettes have one post-catalyst oxygen sensor
Oxygen sensor
An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen in the gas or liquid being analyzed. It was developed by the Robert Bosch GmbH company during the late 1960s under the supervision of Dr. Günter Bauman...

 (although they have two catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...

s), and have a subset of the OBD-II codes implemented. For a 1994 Corvette the implemented OBD-II codes are P0116-P0118, P0131-P0135, P0151-P0155, P0158, P0160-P0161, P0171-P0175, P0420, P1114-P1115, P1133, P1153 and P1158.

This hybrid system was present on the GM H-body
GM H platform (FWD)
The H platform, or H-body designates a General Motors front wheel drive full-sized automobile platform beginning in 1986. It is related to the C, G and K platforms.Previously the H platform designation was used for unrelated rear-wheel drive compact cars....

 cars in 94-95, W-body
GM W platform
The W-body is an automobile platform from General Motors which underpins mid-size cars with front-wheel drive. The platform, originally code named GM10, began in 1982 under Chairman Roger B. Smith and debuted in 1988 with the Pontiac Grand Prix, the Buick Regal, and the Oldsmobile Cutlass Supreme...

 cars (Buick Regal, Chevrolet Lumina ('95 only), Chevrolet Monte Carlo ('95 only), Pontiac Grand Prix, Oldsmobile Cutlass Supreme) in 94-95, L-body
GM L platform
The General Motors L platform was a front-wheel drive compact car automotive platform that was produced from 1987 through 1996....

 (Chevrolet Beretta/Corsica) in 94-95, Y-body
GM Y platform
The Y platform, or Y body, designation has been used twice by the General Motors Corporation to describe a series of vehicles all built on the same basic body and sharing many parts and characteristics...

 (Chevrolet Corvette) in 94-95, on the F-body
GM F platform
The F platform, or F-body, was General Motors' small rear-wheel drive automobile platform from 1967 until 2002. It was based partially on the GM X platform, which was used for compact applications instead of the sporting intent of the F-Body. The only two vehicles to have been built using the...

 (Chevrolet Camaro and Pontiac Firebird) in 95 and on the J-Body
GM J platform
The J platform, or J-body, was General Motors' inexpensive front-wheel drive automobile platform from the 1980s and 1990s. The platform replaced the GM H platform. The J-platform is the only platform of GM to have a model in each of its "Original 5" passenger car divisions...

 (Chevrolet Cavalier and Pontiac Sunfire) and N-Body
GM N platform
The General Motors N platform was a front-wheel drive compact automotive platform produced from 1985 to 2005. The GM N platform replaced the GM X platform....

 (Buick Skylark, Oldsmobile Achieva, Pontiac Grand Am) in 95 and also on '94-'95 Saab vehicles with the normally aspirated 2.3.

The pinout for the ALDL connection on these cars is as follows:
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16


For ALDL connections, pin 9 is the data stream, pins 4 and 5 are ground, and pin 16 is 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 OBD1.5 has also been used on Mitsubishi cars of '95 '97 vintage, some 1995 Volkswagen VR6's and 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 engine and transmission (powertrain), 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. Unlike the OBD-I connector, which was sometimes found under the hood of the vehicle, the OBD-II connector is required to be within 2 foot (0.6096 m) 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:
1. Manufacturer discretion. GM: J2411 GMLAN/SWC/Single-Wire CAN. 9. -
2. Bus positive Line of SAE-J1850 PWM and SAE-1850 VPW 10. Bus negative Line of SAE-J1850 PWM only (not SAE-1850 VPW)
3. Ford DCL(+) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc. Chrysler CCD Bus(+) 11. Ford DCL(-) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc. Chrysler CCD Bus(-)
4. Chassis ground 12. -
5. Signal ground 13. -
6. CAN high (ISO 15765-4 and SAE-J2284) 14. CAN low (ISO 15765-4 and SAE-J2284)
7. K line of ISO 9141-2 and ISO 14230-4 15. L line of ISO 9141-2 and ISO 14230-4
8. - 16. Battery voltage


The assignment of unspecified pins is left to the vehicle manufacturer's discretion.

EOBD


The EOBD (European On Board Diagnostics) 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 2500kg or less) first registered within EU member states since January 1st 2001 for petrol (gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

) engined cars and since January 1st 2004 for diesel engined cars.



For newly introduced models, the regulation dates applied a year earlier - January 1st 2000 for petrol and January 1st 2003 for diesel.

For passenger cars with a Gross Vehicle Weight rating of greater than 2500kg and for light commercial vehicles, the regulation dates applied from January 1st 2002 for petrol models, and January 1st 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 will be lower than previous Euro III and IV.

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.

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) standard is the Australian equivalent of OBD-II.

It applies to all vehicles of category M1 and N1 with a Gross Vehicle Weight rating of 3500kg or less, registered from new within Australia and produced since January 1st 2006 for petrol (gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

) engined cars and since January 1st 2007 for diesel engined cars.



For newly introduced models, the regulation dates applied a year earlier - January 1st 2005 for petrol and January 1st 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 3500kg or less, from July 1st 2008 for new models, July 1st 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.

OBD-II Signal Protocols


There are five signaling protocols that 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
    Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....

     - 41.6 kB/sec, standard of the Ford Motor Company
    Ford Motor Company
    Ford Motor Company is an American multinational automaker based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford and Lincoln brands, Ford also owns a small stake in Mazda in Japan and Aston Martin in the UK...

    )
    • pin 2: Bus+
    • pin 10: Bus–
    • High voltage is +5 V
    • Message length is restricted to 12 bytes, including CRC
      Cyclic redundancy check
      A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...

    • Employs a multi-master arbitration scheme called 'Carrier Sense Multiple Access
      Carrier Sense Multiple Access
      Carrier Sense Multiple Access is a probabilistic Media Access Control protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum."Carrier Sense" describes the fact that a...

       with Non-Destructive Arbitration' (CSMA/NDA)
  • SAE J1850 VPW (variable pulse width - 10.4/41.6 kB/sec, standard of General Motors)
    • 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
      Carrier Sense Multiple Access
      Carrier Sense Multiple Access is a probabilistic Media Access Control protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum."Carrier Sense" describes the fact that a...

      /NDA
  • ISO 9141-2. This protocol has an asynchronous serial data rate of 10.4 kBaud. It is somewhat similar to RS-232
    RS-232
    In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...

    , however the signal levels are different, and communications happens 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 restricted to 12 bytes, including CRC
  • ISO 14230 KWP2000 (Keyword Protocol 2000
    Keyword Protocol 2000
    Keyword Protocol 2000, abbreviated KWP2000, is a communications protocol used for on-board vehicle diagnostics systems . This protocol covers the application layer in the OSI model of computer networking...

    )
    • 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
    Controller Area Network
    Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....

     (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 use 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 OBDII pinouts use the same connector but different pins are utilized 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
Engine control unit
An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...

 (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 parameters that are available 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
OBD-II PIDs
OBD-II PIDs are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J/1979 defines many PIDs, but manufacturers also define many more PIDs specific to their vehicles...

. 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


Here is a basic introduction to the OBD communication protocol according to ISO 15031:

Mode $01 is used to identify what powertrain information is available to the scan tool.

Mode $02 displays Freeze Frame data.

Mode $03 lists the emission-related "confirmed" diagnostic trouble codes stored. It displays exact numeric, 4 digit codes identifying the faults.

Mode $04 is used to clear emission-related diagnostic information. This includes clearing the stored pending/confirmed DTCs and Freeze Frame data.

Mode $05 displays the oxygen sensor monitor screen and the test results gathered about the oxygen sensor.

There are ten numbers available for diagnostics:
  1. $01 Rich-to-Lean O2 sensor threshold voltage
  2. $02 Lean-to-Rich O2 sensor threshold voltage
  3. $03 Low sensor voltage threshold for switch time measurement
  4. $04 High sensor voltage threshold for switch time measurement
  5. $05 Rich-to-Lean switch time in ms
  6. $06 Lean-to Rich switch time in ms
  7. $07 Minimum voltage for test
  8. $08 Maximum voltage for test
  9. $09 Time between voltage transitions in ms


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.

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.

Mode $08 could enable the off-board test device to control the operation of an on-board system, test, or component.

Mode $09 is used to retrieve vehicle information. Among others, the following information is available:
  • VIN (Vehicle Identification Number): 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
    • Gasoline 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.


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.

OBD Applications


Various tools are available that plug in to the OBD connector to access OBD functions. These range from simple generic consumer level tools to highly sophisticated OEM
Original Equipment Manufacturer
An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...

 dealership tools.

Hand-held scan tools


A wide range of rugged hand-held scan tools is available.
  • Simple fault code readers/reset tools are mostly aimed at the consumer level. They may read simple error codes, possibly without translating the meaning, and reset those error codes.
  • 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

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 ELM or STN1110 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 general offer:
  • Large storage capacity for data logging and other functions
  • Higher resolution screen than handheld tools
  • The ability to utilize multiple software programs adding flexibility


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.

In addition to proprietary software tools, free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 applications are available for OBD analysis. Examples include Opendiag, Freediag, and pyOBD.

Data loggers


Data loggers 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 the purpose of 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
    Auto insurance risk selection
    Auto insurance risk selection is the process by which vehicle insurers determine whether or not to insure an individual and what insurance premium to charge. Depending on the jurisdiction, the insurance premium can be either mandated by the government or determined by the insurance company in...

  • Monitoring of driver behaviour by fleet vehicle operators.


Analysis of vehicle black box
Flight recorder
A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of an aircraft accident or incident. For this reason, flight recorders are required to be capable of surviving the conditions likely to be encountered in a severe aircraft...

 data may be performed on a periodic basis, 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.

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
Trip computer
A trip computer is an onboard computer device fitted to cars which can generally record distance travelled, average speed, average fuel consumption, and display real time fuel consumption information...

s, carputer
Carputer
Carputer is the predominant term used to describe a category of mobile computer designed or modified to specifically be installed and run in automobiles...

 or interfaces to PDAs, smartphones, or a Garmin
Garmin
Garmin Ltd. , incorporated in Schaffhausen, Switzerland, is the parent company of a group of companies founded in 1989 by Gary Burrell and Min Kao , that develops consumer, aviation, and marine technologies for the Global Positioning System...

 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.

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
    Controller Area Network
    Controller–area network is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer....

     Physical
    Physical layer
    The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....

     and Data
    Data link layer
    The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....

     Link Layer
  • 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
    J1939
    Society of Automotive Engineers SAE J1939 is the vehicle bus standard used for communication and diagnostics among vehicle components, originally by the car and heavy duty truck industry in the United States....

     - Defines a data protocol for heavy duty commercial vehicles

ISO standards

  • ISO 9141: Road vehicles — Diagnostic systems. International Organization for Standardization
    International Organization for Standardization
    The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

    , 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
      ISO 15765-2
      ISO 15765-2, or ISO-TP, is an international standard for sending data packets over a CAN-Bus. The Protocol allows for the transport of messages that exceed the 8 byte maximum payload of CAN Frames. ISO-TP segments longer messages into multiple frames, adding metadata that allows the interpretation...

    • Part 3: Implementation of unified diagnostic services (UDS on CAN)
    • Part 4: Requirements for emissions-related systems

External links