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 auxiliary transmission fluid pump system supplies the transmission with hydraulic pressure when the vehicle is operating in the internal combustion engine Autostop hybrid mode. The auxiliary transmission fluid pump system consists of a auxiliary transmission fluid pump control module that operates an electric, 12V 3 phase alternating current (AC), motor-driven pump. Two pulse width modulated (PWM) status circuits connect the auxiliary transmission fluid pump control module to the hybrid powertrain control module. The transmission auxiliary oil pump control circuit delivers the hybrid powertrain control module commanded pump speed to the auxiliary transmission fluid pump control module. The transmission auxiliary oil pump diagnostic circuit supplies the hybrid powertrain control module with the actual pump speed and also with the operating status of the auxiliary transmission fluid pump control module. The hybrid powertrain control module monitors these circuits for fault conditions.
The auxiliary transmission fluid pump control module inverts 12V direct current (DC) into 12V, 3 phase ac current to operate the pump motor.
The auxiliary transmission fluid pump control module monitors the status of the auxiliary transmission fluid pump motor/pump as well as its own internal circuitry. The auxiliary transmission fluid pump control module does not store its own diagnostic status. Current ignition cycle diagnostic status is reported to the hybrid powertrain control module over the transmission auxiliary oil pump diagnostic circuit. The diagnostic status within the auxiliary transmission fluid pump control module is reset at every ignition-off cycle.
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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.