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
The accessory dc power control module (APM) converts the energy that flows between the high voltage, 300 volt, direct current (DC) to intermediate voltage, 42 volt, DC to support the electric power steering (EPS). The APM receives a 42 volt enable command from the hybrid powertrain control module (HPCM) over the high speed hybrid GMLAN communication circuit.
The APM continuously monitors the status of its 42 volt circuitry. It will do some diagnostics on this circuitry when the ignition key is first turned to RUN. Additional diagnostics are run while the APM is doing 42 volt conversions after receiving the 42 volt enable command.
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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.