Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the body control module (BCM). The BCM receives 3 signals/circuits from the ignition switch: Acc/Run/Crank (Ignition 0), Run/Crank (Ignition 1) and Acc/Run (Accessory).
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 sequence of switch closures received by the BCM
- The status of the engine run flag
The chart below indicates the modes detected and transmitted by the BCM:
IMPORTANT:
Any ignition switch states not covered in this table indicates a DTC setting situation.
Power Mode Description and Operation
| Power Mode | Engine Run Flag | Sampled Ignition Signal State | ||
| Selected/ Expected | Serial Data | Accessory | Ignition 1 | Ignition 0 |
| OFF | 0 | 0 | 0 | 0 |
| RAP | 0 | 0 | 0 | 1 to 0 |
| ACCESSORY | 0 | 1 | 0 | 1 |
| RUN | 0 | 1 | 1 | 1 |
| CRANK | 0 | 0 | 1 | 1 |
| RUN | 1 | 1 | 1 | 1 |