On-board diagnostics

On-board diagnostics (OBD) is an automotive term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or repair technician access to the status of the various vehicle subsystems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s versions of on-board vehicle computers. Early versions of OBD would simply illuminate a malfunction indicator light or "idiot 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 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

Standard interfaces

ALDL

Main article: ALDL

GM's ALDL (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 powertrain control modules (aka PCM, ECM, ECU). Different versions had slight differences in pin-outs and data rates. Earlier versions used 160 bit/s, while later versions went up to 8192 bit/s and used bi-directional communications to the PCM.[7][8]

M-OBD

Multiplex OBD or M-OBD is an OBD variant protocol used by Toyota, prior to OBD-II compliance.[9][10][11] Toyota's DLC3 (Data Link Connector 3) is the standard 16-pin OBD-II connector, but a proprietary cable and software is required as generic OBD-II cables and software will not interface with it. The bus + line is SIL (Pin 7)[12]

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 Diagnostic Trouble Codes (DTCs) 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 DTCs from the vehicle. DTCs 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 DTCs of some OBD-I cars are interpreted in different ways, however. Cadillac (gasoline) fuel-injected vehicles 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 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 DTCs available than for OBD-II equipped vehicles.

OBD-1.5

OBD 1.5 refers to a partial implementation of OBD-II which General Motors 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 (although they have two catalytic converters), 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.[13]

This hybrid system was present on the GM H-body cars in 94-95, W-body cars (Buick Regal, Chevrolet Lumina ('95 only), Chevrolet Monte Carlo ('95 only), Pontiac Grand Prix, Oldsmobile Cutlass Supreme) in 94-95, L-body (Chevrolet Beretta/Corsica) in 94-95, Y-body (Chevrolet Corvette) in 94-95, on the F-body (Chevrolet Camaro and Pontiac Firebird) in 95 and on the J-Body (Chevrolet Cavalier and Pontiac Sunfire) and N-Body (Buick Skylark, Oldsmobile Achieva, Pontiac Grand Am) in 95 and 96 and also on '94-'95 Saab vehicles with the naturally 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.[14]

An OBD 1.5 has also been used on Mitsubishi cars of '95 '97 vintage, some 1995 Volkswagen VR6's and in the Ford Scorpio since 95.[15]

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

Female OBD-II connector on a car
Type A female connector
Type B female connector

The SAE J1962 specification provides for two standardized hardware interfaces, called type A and type B. Both are female, 16-pin (2x8), D-shaped connectors, and both have a groove between the two rows of pins. But type B has the groove interrupted in the middle, so you can't plug a type A male connector into a type B socket. You can, however, mate a type B male plug in a type A female socket.

The type A connector is used for vehicles that use 12V supply voltage, whereas type B is used for 24V vehicles and it is required to mark the front of the D-shaped area in blue color.

SAE J1962 defines the pinout of the connector as:

Female OBD-II connector pinout - front view
1 Manufacturer discretion:
  • GM: J2411 GMLAN/SWC/Single-Wire CAN[16]
  • VW/Audi/BMW: Switched +12V to tell a scan tool whether the ignition is on.
  • Ford, FIAT: Infotainment CAN High[16]
 9 Manufacturer discretion:
  • BMW: TD (Tachometer Display) signal aka engine RPM signal.
  • GM: 8192 bit/s ALDL where fitted.
  • Ford: Infotainment CAN-Low
2 Bus Positive Line of SAE J1850 PWM and VPW 10 Bus Negative Line of SAE J1850 PWM only (not SAE J1850 VPW)
3 Manufacturer discretion:
  • Ford: DCL(+) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc.
  • Ford: Medium Speed CAN-High[16]
  • Chrysler: CCD Bus(+)[16]
 11 Manufacturer Discretion:
  • Ford: DCL(-) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc.
  • Ford: Medium Speed CAN-Low[16]
    Chrysler: CCD Bus(-)[16]
4 Chassis ground 12 Manufacturer discretion:
5 Signal ground 13 Manufacturer discretion:
  • Ford: FEPS – Programming PCM voltage
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 Manufacturer discretion:
  • BMW: Second K-Line for non OBD-II (Body/Chassis/Infotainment) systems.
  • FIAT: Infotainment CAN-Low.
 16 Battery voltage:
  • Type "A" 12V/4A
  • Type "B" 24V/2A

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 feet (0.61 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).

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 2500 kg or less) first registered within EU member states since January 1, 2001 for petrol (gasoline) engined cars and since January 1, 2004 for diesel engined cars.[17]

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 will be 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.

The following two characters would refer to the individual fault within each subsystem.[18]

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) 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 3500 kg or less, registered from new within Australia and produced since January 1, 2006 for petrol (gasoline) engined cars and since January 1, 2007 for diesel engined cars.[19] 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.[20] 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:

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

Main article: OBD-II PIDs

OBD-II provides access to data from the engine control unit (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. 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:

OBD 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

Multi-brand vehicle diagnostics system handheld Autoboss V-30 with adapters for connectors of several vehicle manufacturers.[21]
Simple, rugged multi-brand handheld scanner

A range of rugged hand-held scan tools is available.

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 adaptor cables, bluetooth or WiFi adapters plugged into the car's OBD II connector.

PC-based scan tools and analysis platforms

Typical simple USB KKL Diagnostic Interface without protocol logic for signal level adjustment.

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[22] 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:

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

TEXA OBD log. Small data logger with the possibility to read out the data later on PC via USB.

Data loggers are designed to capture vehicle data while the vehicle is in normal operation, for later analysis.

Data logging uses include:

Analysis of vehicle black box 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.

In the Netherlands, 2006 and later vehicles get a yearly EOBD emission check.[26]

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 computers,[27] carputer or interfaces to PDAs,[28] smartphones, or a GPS 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 is no longer only used by professionals and hobbyists to repair vehicles. 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. OBD II is also monitored to block mobile phones when driving and to record trip data for insurance purposes.[29]

Standards documents

SAE standards documents on OBD-II

SAE standards documents on HD (heavy duty) OBD

ISO standards

Security issues

Researchers at the University of Washington and University of California 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 into the engine control units. Their conclusion is that vehicle embedded systems are not designed with security in mind.[30][31][32]

There have been reports of thieves using specialist OBD reprogramming devices to enable them to steal cars without the use of a key.[33] 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 and authorization in the OBD specifications, which instead rely largely on security through obscurity.[34] The National Highway Traffic Safety Administration has demonstrated the ability to take over certain functions through wires to the car's control center.[35]

See also

Wikimedia Commons has media related to Obd2.

References

  1. ↑ http://www.arb.ca.gov/msprog/obdprog/obdfaq.htm
  2. ↑ http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1998L0069:19981228:EN:PDF
  3. ↑ http://www.iso.org/iso/catalogue_detail?csnumber=33619
  4. ↑ http://www.epa.gov/fedrgstr/EPA-AIR/2005/December/Day-20/a23669.htm, U.S. EPA regulations requiring ISO-15676 CAN standard to be supported for all U.S. sold cars model year 2008 and later.
  5. ↑ http://english.mep.gov.cn/inventory/Catalogue_Standards/200807/t20080718_125885.htm
  6. ↑ http://baike.baidu.com/view/171354.htm, Chinese news article on implementation of OBD (Google translation http://translate.google.com/translate?hl=en&sl=zh&tl=en&u=http://baike.baidu.com/view/171354.htm)
  7. ↑ http://www.webpg.net/ALDLbareINST.pdf
  8. ↑ http://www.techedge.com.au/vehicle/aldl160/160serial.htm
  9. ↑ http://www.pradopoint.com/showthread.php?35863-Prado-90-OBDI-vs-OBDII-TDCL-vs-MOBD
  10. ↑ http://www.moranbahweather.com/toyota/lc_trj12/rm/rm990e/m_05_0429.pdf
  11. ↑ http://4wdaction.com.au/forum/viewtopic.php?f=44&t=53117
  12. ↑ https://www.scantool.net/forum/index.php?topic=2364.0
  13. ↑ 1994 Corvette Service Manual, Book 2. General Motors Corporation. December 1993. pp. 6E3–A–166 : 6E3–A–223.
  14. ↑ 1994 Corvette Service Manual, Book 2. General Motors Corporation. Dec 1993. pp. 6E3–A–11.
  15. ↑ EEC IV Code Reader: For 2.9L 12 Valve & Early Tdi, Ford Scorpio
  16. 1 2 3 4 5 6 OpenXC Platform: Supported Vehicle Interfaces
  17. ↑ "Directive 98/69/EC of the European Parliament". Publications Office of the European Parliament.
  18. ↑ http://www.obd-codes.com/trouble_codes/
  19. ↑ "Vehicle Standard (Australian Design Rule 79/01 – Emission Control for Light Vehicles) 2005". Australian Government ComLaw.
  20. ↑ "Vehicle Standard (Australian Design Rule 79/02 – Emission Control for Light Vehicles) 2005". Australian Government ComLaw.
  21. ↑ "Autoboss 30 Diagnostic Coverage List" (PDF).
  22. ↑ STN1110 specifications
  23. ↑ http://www.progressive.com/myrate/myrate-default.aspx an auto insurer's OBD-II data-logging
  24. ↑ http://iosix.com/ a personal/fleet OBD-II datalogger
  25. ↑ http://www.teensafedriver.com an auto insurer's in-car camera
  26. ↑ http://www.diagnoseapparatuur.nl/EOBD-General-Periodic-Inspection EOBD General Periodic Inspection rules
  27. ↑ OBDuino open source OBD trip computer
  28. ↑ www.qcontinuum.org/obdgauge/index.htm open source PDA app showing OBD-based gauges
  29. ↑ http://www.obdexperts.co.uk/docs/white_papers/Is_Your_Tracking_Lacking_letter.pdf
  30. ↑ Bright, Peter (15 May 2010). "Car hacks could turn commutes into a scene from Speed". Ars Technica. Retrieved 23 Aug 2012.
  31. ↑ Mastakar, Gaurav (6 Apr 2012). "Experimental Security Analysis of a Modern Automobile". University of Washington and University of California, San Diego. Retrieved 23 Aug 2012.
  32. ↑ Marks, Paul (17 July 2013). "$25 gadget lets hackers seize control of a car". New Scientist. Retrieved 5 November 2013.
  33. ↑ "Pistonheads report into thefts via obd". Retrieved 2 July 2012.
  34. ↑ Van den Brink, Rob. "Dude, Your Car is Pwnd" (PDF). SANS Institute. Archived from the original (PDF) on 2014-08-23. Retrieved 2015-08-05.
  35. ↑ Travers, Jim (May 7, 2015). "Kee". Consumer Reports. Retrieved 29 May 2015.
Notes
  • Birnbaum, Ralph and Truglia, Jerry. Getting to Know OBD II. New York, 2000. ISBN 0-9706711-0-5.
  • SAE International. On-Board Diagnostics for Light and Medium Duty Vehicles Standards Manual. Pennsylvania, 2003. ISBN 0-7680-1145-0.

External links

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