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 Power Module (APM) controls the energy flowing between the high voltage, 300-volt, direct current (DC) and 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. APM functions will run only when the APM Enable is active on the high speed hybrid GMLAN communication circuit.
Heat is generated in the 42-volt APM circuit solely through the demand for use of the EPS. The Engine Control Module (ECM) measures the temperature of the Power Electronics Cooling Loop and commands the flow of 2 electrical coolant pumps. The APM transfers heat in the 42-volt circuit to the APM Heat Plate which is then dissipated at the Power Electronics Front End Heat Exchanger.
Based on the severity of an overheat condition in the 42-volt circuit, the APM will make decisions ranging from notification of an over temperature condition to the EPS to completely shutting down the 42-volt power conversion.
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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.