OBDII Bus Description OBD2 On-Board Diagnostics II defines a communications protocol and a standard connector to acquire data from passenger cars. OBD was required by U.S. EPA on all gasoline powered cars and light duty trucks manufactured for the U.S.
After 1996 to help monitor/inspect vehicle emissions as required by the Clean Air Act Amendments of 1990. OBDII is the second generation of the OBD specification.
The first generation OBD monitored fewer emission related components, was not calibrated to a specific level of emission performance, and was not as fell defined. Any passenger cars and truck produced after 1996 uses the OBD II standard. The OBD-II standard allows for multiple electrical interfaces, which complicates the hardware used to interface with the vehicle.
OBDII will light a warning lamp called a MIL (malfunction indicator lamp), also known as the 'check engine' light on the dash. A scan-tool may also be used to probe the OBDII connector OBDII data as defined by the SAE J1979 standard. The warning light may come on for any number of reasons and manufacturers recommend having the vehicle serviced as soon as possible. However; the Check Engine light could also come on for such simple reasons as filling the tank while the vehicle is running, or leaving the gas cap off. It may take up to three days for the light to go back off, after coming on for a missing gas cap. The OBD II interface is located in the cab, and must be located with in a certain area within the cab. OBDII pinout, Signal Assignments.
Bus positive Line of SAE-J1850. Chassis ground. Signal ground. CAN high (ISO 15765-4 and SAE-J2234). K line of ISO 9141-2 and ISO 14230-4. Bus negative Line of SAE-J1850.
CAN low (ISO 15765-4 and SAE-J2234). L line of ISO 9141-2 and ISO 14230-4. Battery voltage The pinout assignment of unspecified pins is left to the vehicle manufacturer's discretion., Scanners, Code Readers and so on.
J1962 - describes the standardized 16-pin trapezoidal connector. The male plug is use to connect to your car computer and the female is for making an extension cable or some other device The J1850 VPW single wire protocol, used by GM may be found on an OBDII bus, if so the connector will have contacts in pins 2, 4, 5, and 16, with no contact in pin 10.
The J1850 PWM two wire protocol, used by Ford may be found on an OBDII bus, if so the connector will have contacts in pins 2, 4, 5, and 10, with no contact in pin 16. The ISO 9141-2 single wire protocol, used by Chrysler may be found on an OBDII bus, if so the connector will have contacts in pins 4, 5, 7, 15 and 16. The protocol and command set is fixed by SAE J1979, so they are the same for all three protocols, only the electrical layers are changed. The may also be found on the OBDII bus J1850 bus Description The bus is used for diagnostics and data sharing applications in vehicles. The J1850 bus takes two forms; A 41.6Kbps Pulse Width Modulated (PWM) two wire differential approach, or a 10.4Kbps Variable Pulse Width (VPW) single wire approach.
The single wire approach may have a bus length up to 35 meters (with 32 nodes). A high resides between 4.25 volts and 20 volts, a low is any thing below 3.5 volts.
High and low values are sent as bit symbols (not single bits). Symbols times are 64uS and 128uS for the single wire approach. The ISO 9141-2 single-wire asynchronous interface operates at 10.4kbps OBDII Related Standards J1962 - SAE (Society of Automotive Engineers) standard defining the physical connector used for the OBDII interface. J1850 - SAE standard for the Class B Communications Network Interface (standard defines the actual J1850 signaling and timings) J1939, ISO 11898 J1978 - SAE standard for OBD II scan tools J1979 - SAE standard for diagnostic test modes J2012 - SAE standard for EPA emission test report format.
Does My Car Have OBD-II? All cars and light trucks built and sold in the United States after January 1, 1996 were required to be OBD II equipped. In general, this means all 1996 model year cars and light trucks are compliant, even if built in late 1995. Two factors will show if your vehicle is definitely OBD II equipped: 1) There will be an OBD II connector as shown below, and 2) There will be a note on a sticker or nameplate under the hood: 'OBD II compliant'.
The Connector Pin 2 - J1850 Bus+ Pin 4 - Chassis Ground Pin 5 - Signal Ground Pin 6 - CAN High (J-2284) Pin 7 - ISO 9141-2 K Line Pin 10 - J1850 Bus Pin 14 - CAN Low (J-2284) Pin 15 - ISO 9141-2 L Line Pin 16 - Battery Power Where is the connector located? The connector must be located within three feet of the driver and must not require any tools to be revealed.
Look under the dash and behind ashtrays. The Five Flavors of OBD II While the parameters, or readings, required by OBD II regulations are uniform, the auto manufacturers had some latitude in the communications protocol they used to transmit those readings to scanners. Naturally, each felt they had the one true way, so we have five different OBD II communications protocols in use. The big scanner consoles costing thousands of dollars include the decoding software and firmware for all five protocols in their units, making them universal.
Less expensive units, for home or small shop use, are usually customized for a specific communications protocol. Be sure the scanner you are using suits the protocol of your car. As a rule of thumb, GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation). Chrysler products and all European and most Asian imports use ISO 9141 or KWP2000 circuitry. Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns. All 2008 and newer model year vehicles use CAN.
There are some variations among captive imports such as the Cadillac Catera, a German Opel derivative, which uses the European ISO 9141 protocol. If you have first hand knowledge of other such variations, please and, together, we can build a more complete listing. On 1996 and later vehicles, you can tell which protocol is used by examining the OBD II connector:. J1850 VPW -The connector should have metallic contacts in pins 2, 4, 5, and 16, but not 10. ISO 9141-2/KWP2000 -The connector should have metallic contacts in pins 4, 5, 7, 15, and 16.
J1850 PWM -The connector should have metallic contacts in pins 2, 4, 5, 10, and 16. CAN -The connector should have metallic contacts in pins 4, 5, 6, 14 and 16.
Obd Ii Diagnostic Interface
If your vehicle has this style connector, but doesn't have these pins populated, you probably have a pre-OBDII vehicle. To add some confusion, even having the connector with the contacts shown above is not a guarantee of OBD II compliance.
Obd Ii Interface Kit
This style connector has been seen on some pre-1996 vehicles which were not OBD II compliant. Information on Pre-96 Cars A reader with the California Air Resouces Board provided this list of pre-96 OBD II engine designations. Note that CARB recognizes engine series, rather than vehicle models, so the engine designations are the true key, with the vehicle models provided as a courtesy. California Air Resources Board List of Certified OBD II Complying Engine Families and Models.
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Iso 9141 2 Protocol Document
Engine Family Manufacturer Model(s) Fully Compliant?