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 Master
Power to many of this vehicles circuits is controlled by the module that is designated the power mode master. This vehicles power mode master is the body control module (BCM). The BCM has multiple B+ circuits that feed into it. Each of those circuits are partitioned within the controller to drive certain outputs of the vehicle's body functions. An open or short in any one of the B+ circuits may induce multiple codes/or a section of non-functionality within the BCM with the rest of the BCM functioning normally. In this case it is useful to refer to the power distribution schematics to determine if the non-functional partition of the controller shares a common B+ circuit. The ignition mode switch is a low current switch with a discrete ignition signal to the power mode master for determination of the power mode that will be sent over the serial data circuits to the other modules that need this information. The power mode master will also activate relays and other direct outputs of the power mode master as needed. The power mode master determines which power mode (Off, Accessory, Run/Start) is required, and reports this information to other modules via serial data. Modules which have switched voltage inputs may operate in a default mode if the power mode serial data message does not match what the individual module can see from its own connections.
The power mode master receives ignition mode switch signals to identify the operators desired power mode. The Power Mode Parameter table below illustrates the correct state of these input parameters in correspondence to the ignition mode switch with the transmitter to vehicle range:
| Power Mode | Power Mode Transmitted | Push Button Ignition Switch (Power Button Switch Circuit Input to the BCM) |
Push Button Ignition Switch Voltage Push Button Ignition Switch Voltage Input to the BCM |
Key in Cylinder Switch/Key Fob in Vehicle (Transmitter in Range to the BCM Signal) |
|---|---|---|---|---|
| Transmitter in Range | Off | Inactive | 9 V | Yes |
| Transmitter out of Range | Off | Inactive | 9 V | No |
| Vehicle On Power Mode, then Press the Power Button Switch (Foot on or off the Brake Pedal) Transmitter in Vehicle | Off | Active (pushed) / Inactive (not pushed) | 5-6 V (pressed) | Yes |
| Vehicle Off Power Mode, then Press the Power Button Switch with foot off the Brake Pedal; Transmitter in Vehicle | Accessory Mode | Active (pushed) / Inactive (not pushed) | 5-6 V (pressed) | Yes |
| Vehicle Off Power Mode, then Press the Power Button Switch with foot on the Brake Pedal; Transmitter in Vehicle | Vehicle in Run/Start Mode (Ignition ON engine running.) | Active (pushed) / Inactive (not pushed) | 5-6 V (pressed) | Yes |
| Vehicle OFF Power Mode, then Press and Hold the Power Button Switch for 5 s with foot OFF the Brake Pedal; Transmitter in Vehicle | Vehicle in Run/Start Mode (Ignition ON without the engine running) | Active (pushed) / Inactive (not pushed) | 5-6 V (pressed) | Yes |
| Vehicle OFF Power Mode, then Press and Hold the Power Button Switch for 10 s with foot OFF the Brake Pedal; Transmitter in Vehicle | Vehicle In Service Mode (Ignition ON without the engine running) | Active (pushed) / Inactive (not pushed) | 5-6 V (pressed) | Yes |
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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.