anyone know how many volts i should be getting to the scan tool connecting in a '96 caprice classic. i am only getting around 4 at the tan bottom left wire to the scan tool connector. i checked the wire and am getting the same up until a big connector. i also check the PCM and am getting around 5 from there, if anyone has any idea how much voltage is requiered for the scan tool to turn on, or how to fix my problem please help.

http://72.19.213.157/files/OBD-IIPinout.jpg

As a general rule, GM cars and light trucks use SAEJ1850 VPW (Variable Pulse Width Modulation). Chrysler products, European products, and most Asian imports use the ISO 9141 scheme. Ford uses SAEJ1850 PWM (Pulse Width Modulation) communication patterns. In MY 2008, all vehicles will use a CAN (Controller Area Network) bus, similar to RJ-485 serial data communication.

There are some corporate imports, such as the Cadillac Catera (an Opel derivative) and GTO (Holden), which use the European ISO 9141 protocol.

On 1996 and later vehicles, you can identify the signal protocol used by examining the OBD-II connector:

* J1850 VPW--The connector should have metallic contacts in 2, 4, 5, and 16, but not 10.
* ISO 9141-2--The connector should have metallic contacts in 4, 5, 7, 15, and 16.
* J1850 PWM--The connector should have metallic contacts in 2, 4, 5, 10, and 16.

If a vehicle has this style 16-pin connector, but doesn't have the necessary pins inserted, it is probably a pre-OBDII vehicle. To add some confusion, even having the connector with the contacts shown above is not a guarantee of full OBD II compliance. This style connector had been used on some 1994-95 vehicles which were not completely OBD II compliant. A '96 IS fully OBD-II, however.

Most scanning equipment requires the supply of 12VDC between pins 16 and 5 (ground) for operation.