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.
Circuit Description
When the ignition switch is turned to the Start position, the body control module (BCM) receives battery voltage on the ignition 1 voltage circuit, and less than 5 volts on the off/run/crank voltage circuit. The BCM supplies voltage to energize the RUN/CRANK Relay 32. The BCM sends a high speed GMLAN serial data message to the engine control module (ECM) that the key is in the start position. The ECM receives the message from the BCM, and also receives a serial data message from the transmission control module (TCM) containing the shift lever position. If the shift lever is in Park or Neutral when ignition switch is turned to Start, the ECM supplies voltage to the START Relay 31. The START relay supplies voltage to the S terminal of the starter solenoid, through the 30 A STRTR Fuse 26, in order to crank the engine.
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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.