Protocol

OBD-II: All Vehicles Manufactured after 1996 conformed to OBD-II standards. Although vehicles manufactured before 1996 may have the connector most do not comply to all OBD-II standards.
SAE J1850 VPW - Used on GM Cars and Light Trucks
SAE J1850 PWM - Used on FORD
ISO 9141-2 - Used on Chrysler vehicles, All European and most Asian car.
ISO 14230 KWP2000 (Keyword Protocol 2000) - Communication by serial line. Many ISO9141-2 manufacturers moved to this protocol.

CAN BUS
ISO 15765 CAN - Controller Area Network is a new protcol being used in order to eliminate the ambiguity current protocols. By the year 2008 all vehicles sold in the United States will be required to implement CAN bus.

Pin Summary
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 +

More CAN-bus details
Controller–area network (CAN or CAN-bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.

CAN is a message based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment.

Development of the CAN-bus started originally in 1983 at Robert Bosch GmbH. The protocol was officially released in 1986 at the Society of Automotive Engineers (SAE) congress in Detroit, Michigan. The first CAN controller chips, produced by Intel and Philips, came on the market in 1987. Bosch published the CAN 2.0 specification in 1991.

CAN is used in the OBD-II vehicle diagnostics standard, mandatory for all cars and light trucks sold in the United States since 1996, and the EOBD standard, mandatory for all petrol vehicles sold in the European Union since 2001 and all diesel vehicles since 2004.

Looking for a DTC Code
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Trouble Code Formulation Summary
The first character shows which area of the vehicle generated the code.
P PowerTrain
B Body
C Chassis
U Network

The next Character can be a 0 or a 1, 2, 3
0 Standard (SAE) OBD code
1,2,3 Manufacturers own code

If the first character was P (PowerTrain) then the next will be a number
0 Fuel and Air Metering
1 Fuel and Air Metering
2 Injector Fuel and Air Metering Circuit
3 Ignition System and Misfire Detection
4 Auxilliary Emission Controls
5 Vehicle Speed control and Idle Control System
6 Computer Output Circuit
7,8,9 Transmission Related Faults

The last two numbers which will identify the specific fault by the onboard control system.
P 0 1 7 0
1  2 3 4 5

1st digit
P = powertrain
B = Body
C = Chassis

2nd digit
0 = Standard
1 = Manufacturer specific

3rd digit
1 = Emission management
2 = Injector circuit
3 = Ignition
4 = Auxiliary emission
5 = Vehicle speed & idle control
6 = Computer & output circuit
7,8,9 = Transmission

Additional CAN BUS Details
There are several CAN physical layer standards listed below:
    * ISO 11898-1: CAN Data Link Layer and Physical Signalling
    * ISO 11898-2: CAN High-Speed Medium Access Unit
    * ISO 11898-3: CAN Low-Speed, Fault-Tolerant, Medium-Dependent Interface
    * ISO 11898-4: CAN Time-Triggered Communication
    * ISO 11898-5: CAN High-Speed Medium Access Unit with Low-Power Mode
    * ISO 11992-1: CAN fault-tolerant for truck/trailer communication
    * ISO 11783-2: 250 kbit/s, Agricultural Standard
    * SAE J1939-11: 250 kbit/s, Shielded Twisted Pair (STP)
    * SAE J1939-15: 250 kbit/s, UnShielded Twisted Pair (UTP) (reduced layer)
    * SAE J2411: Single-wire CAN (SWC)

ISO 11898-2 uses a two-wire balanced signaling scheme. It is the most used physical layer in car powertrain applications and industrial control networks.

ISO 11898-4 standard defines the time-triggered communication on CAN (TTCAN). It is based on the CAN data link layer protocol providing a system clock for the scheduling of messages.

SAE J1939 standard uses a two-wire twisted pair, -11 has a shield around the pair while -15 does not. SAE 1939 is widely used in agricultural & construction equipment.

ISO 11783-2 uses four unshielded twisted wires; two for CAN and two for terminating bias circuit (TBC) power and ground. This bus is used on agricultural tractors. This bus is intended to provide interconnectivity with any implementation adhering to the standard.

Where is the OBD 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.