Circuit Description
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) is the power mode master responsible for sending ignition switch position information on the class 2 serial data link. The BCM monitors 3 discrete wires from the ignition switch contacts and the engine run flag (ERF) in order to determine the present power mode. The BCM communicates this power mode information to all class 2 modules on the class 2 serial data link. The following table represents correct BCM power mode data:
Correct Ignition Switch Inputs
| Ignition Switch Position | BCM Input and Scan Tool Display | ||
|---|---|---|---|
| Ignition Accessory | Ignition 1 | Ignition 0 | |
| OFF | Inactive | Off | Off |
| UNLOCK | Inactive | Off | On |
| ACC | Active | Off | On |
| ON | Active | On | On |
| START | Inactive | On | On |