Power Steering Control Module

The accessory power module (APM) provides a shielded, 42-volt circuit to the power steering control module (PSCM) to drive the power steering motor. The PSCM also uses the 12-volt battery circuit to power the module electronics. The normal operation voltage range the APM provides to the PSCM is between 40-44 volts. The APM is not capable of handling more than 58 volts. The dynamic brake circuit of the PSCM is used to keep the reverse motor voltage of the electric power steering system below 58 volts, and will start to consume the surplus voltage if the 42-volt circuit rises in a range between 50-58 volts.

The APM is also monitored by the hybrid control module (HCM) to detect overheating. If overheating of the APM is detected, the HCM sends a serial data message to the PSCM via the serial data gateway module as the power output to the PSCM is reduced until the APM returns to a normal operating temperature. The PSCM will reduce power assist according to the reduced output power provided by the APM, and will return to full steering assist when the APM returns to normal operating temperature.

The PSCM uses a combination of commanded motor voltage and current levels to calculate an estimated power steering system temperature. Neither the PSCM nor the power steering motor are designed to handle around 60-amps continuously and will enter into overload protection mode if the system is exposed to exclusive static steering conditions. If the steering wheel is turned to its maximum rotation point and held at this position for an extended period of time, the PSCM will reduce the amount of current commanded to the power steering motor, which reduces the amount of steering assist as well as system temperature. The PSCM has the ability to detect malfunctions within the power steering system. Any malfunction detected will cause the SERVICE POWER STEERING message to be displayed on the driver information center (DIC).