ODB
Communication Protocols and Connectors

There are FIVE OBD-II communication protocols, and TWO versions of the connector (A and B):

  1. PWM = J1850 (Pulse Width Modulated)
  2. VPW = J1850 (Variable Pulse Width)
  3. ISO = 9141
  4. ISO 14230 (also known as Keyword Protocol 2000)
  5. CAN (ISO 15765 / SAE J2480)

To tell which protocol you have, see the table below:

Standard Pin 2 Pin 7 Pin 10 Pin 15 Notes
PWM must have NONE must have NONE The connector must have pins 2,4,5,10, and 16
VPW must have NONE NONE NONE The connector must have pins 2, 4, 5, and 16, but not 10.
ISO NONE must have NONE may have The connector must have pins 4, 5, 7, and 16. Pin 15 may or may not be present.

OBDII pinout and Signal Assignments:
  1. ***
  2. Bus positive Line of SAE-J1850
  3. ***
  4. Chassis ground
  5. Signal ground
  6. CAN high (ISO 15765-4 and SAE-J2234)
  7. K line of ISO 9141-2 and ISO 14230-4
  8. ***
  9. ***
  10. Bus negative Line of SAE-J1850
  11. ***
  12. ***
  13. ***
  14. CAN low (ISO 15765-4 and SAE-J2234)
  15. L line of ISO 9141-2 and ISO 14230-4
  16. Battery voltage

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

J1962 - describes the standardized 16-pin trapezoidal connector.
The male plug is used to connect to your car computer and the female is for making an extension cable or some other device

ODB-II connector types:

TYPE A:

TYPE B:

  • ODB-I connector which GM calls a ALDL connector.
  • Their are THREE types avail, 5 pin, 10 pin and 12 pin, the 12 pin is shown below:


    1. A = Ground.
    2. B = Diagnostic Terminal.
    3. C = A.I.R (Air Injection).
    4. D = Service Engine Soon Lamp (maybe).
    5. E = Serial Data.
    6. F = T.C.C. (maybe).
    7. G = Fuel Pump (maybe).
    8. H = Brake Sense Speed Input (CK maybe).
    9. J = N/A.
    10. K = N/A.
    11. L = N/A.
    12. M = Serial Data (L4 Use Special Tool).
    Funny that the letter "I" is ommited, eh ?

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