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/System Description
This vehicle does not use a 12V starter motor to crank the internal combustion engine (ICE). A much more powerful 300V motor generator located within the transmission is utilized to crank the engine. The 300V motor generator can rotate the engine to operating speed, 800 RPM, within just a few hundred milliseconds. The 300V motor generator allows near-instant starting of the engine.
The body control module (BCM) monitors the position of the ignition switch. When the ignition switch is placed in the Crank position, the BCM sends out a Crank-Request message over GMLAN. The hybrid powertrain control module (HPCM) responds to this GMLAN message by applying torque to drive motor generator 1 located within the transmission. Drive motor generator 1 is mechanically linked to the engine crankshaft.
The HPCM will not respond to the BCM Crank-Request GMLAN message if certain vehicle conditions exist such as the transmission gear selector position does not equal Park or Neutral or certain DTCs are set.
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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.