Serial Data Power Modes
WARNING: This page is about a different car, the 2004 GMC Safari and 2004 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the body control module (BCM) is the PMM. The BCM receives 2 signals/circuits from the ignition switch. These are the ignition 1 and ignition 3 signals/circuits.
To determine the correct power mode the BCM uses:
- The state of these signals/circuits, either switch closed (B+ = 1) or switch open (open = 0)
- The status of the engine run flag
The chart indicates the modes detected and transmitted by the BCM:
Correct Ignition Switch Inputs
| Ignition Key Position | Power Mode Parameter | Engine Run Flag Serial Data | Sampled Ignition Signal State | |
|---|---|---|---|---|
| Ignition 1 | Ignition 3 | |||
| Off | Off-Awake | 0 | 0 | 0 |
| Unlock | Off-Awake | 0 | 0 | 0 |
| Accessory | Off-Awake | 0 | 0 | 0 |
| Run | Run | 0 | 1 | 1 |
| Crank | Crank | 0 | 1 | 0 |
| Run | Run | 1 | 1 | 1 |