Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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 PMM receives two signals/circuits from the ignition switch. These are the Ignition 1 and Ignition 2 ignition switch signals/circuits.
To determine the correct power mode the PMM uses:
- The state of these signals/circuits, either switch closed (B+ = 1) or switch open (B+ = 0)
- The sequence of switch closures received by the PMM
- The status of the engine run flag
The chart below indicates the modes detected and transmitted by the PMM:
| Power Mode Selected/Expected | Engine Run Flag Serial Data | Sampled Ignition Signal State | Power Mode State | Key-In Sense | |
|---|---|---|---|---|---|
| Ignition 1 | Ignition 2 | ||||
| OFF | 0 | 0 | 0 | OFF-AWAKE | NA |
| RAP | 0 | 0 | 1-0 | RAP | NA |
| UNLOCK | 0 | 0 | 0-1 | UNLOCK | NA |
| ACCESSORY | 0 | 0 | 1 | ACCESSORY | NA |
| RUN | 1 | 1 | 1 | RUN | NA |
| RUN | 0 | 1 | 1 | RUN | NA |
| CRANK | 0 | 1 | 1-0 | CRANK | NA |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.