Circuit/System Description

WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

The auxiliary transmission fluid pump (ATFP) system supplies the transmission with hydraulic pressure when the vehicle is operating in the internal combustion engine (ICE) Autostop hybrid mode. The ATFP system consists of a ATFP control module that operates an electric, 12V 3 phase alternating current (ac), motor-driven pump. Two pulse width modulated (PWM) status circuits connect the ATFP control module to the hybrid powertrain control module (HPCM). The transmission auxiliary oil pump (TAOP) control circuit delivers the HPCM commanded pump speed to the ATFP control module. The transmission auxiliary oil pump (TAOP) diagnostic circuit supplies the HPCM with the actual pump speed and also with the operating status of the ATFP control module. The HPCM monitors these circuits for fault conditions.

The ATFP control module inverts 12 v direct current (dc) into 12 v, 3 phase ac current to operate the pump motor.

The ATFP control module monitors the status of the ATFP pump as well as its own internal circuitry. The ATFP control module does not store its own diagnostic status. Current ignition cycle diagnostic status is reported to the HPCM on the TAOP diagnostic circuit. The diagnostic status within the ATFP control module is reset at every ignition-off cycle.