System Operation
Electronic Power Assist Steering (EPAS) System
System Operation
System Diagram
Network Message Chart
Module Network Input Messages: PSCM (Power Steering Control Module)
Electronic Power Assist Steering (EPAS) System
The PSCM (Power Steering Control Module) controls the functions of the EPAS (Electronic Power Assist Steering) system and communicates with other modules over the HS-CAN (High Speed Controller Area Network).
To activate the EPAS (Electronic Power Assist Steering) system, a 12-volt hot at all times and a 12-volt ignition/run input to the PSCM (Power Steering Control Module) is required. The PSCM (Power Steering Control Module) then monitors the HS-CAN (High Speed Controller Area Network) to determine if the vehicle is operating in a manner capable of supporting the EPAS (Electronic Power Assist Steering) system.
The PSCM (Power Steering Control Module) uses inputs from various modules over the HS-CAN (High Speed Controller Area Network), the steering torque sensor and the motor to determine the amount or level of assist provided by the EPAS (Electronic Power Assist Steering) system.
The steering torque sensor sends out 2 signals, one for left and one for right. When the steering wheel is turned to the left, the left signal increases while the right signal decreases. When the steering wheel is turned to the right, the right signal increases while the left signal decreases. This allows the PSCM (Power Steering Control Module) to determine if the driver intends to turn left or right in order to spin the motor in the appropriate direction.
The EPAS (Electronic Power Assist Steering) gear uses a 12-volt reversible motor to control the steering effort. The motor is connected to the rack of the steering gear by a toothed belt and pulley/bearing assembly. The motor is used by the PSCM (Power Steering Control Module) to move the rack inside the steering gear housing. The position of the motor is used to determine steering wheel angle/position instead of using a separate sensor.
The PSCM (Power Steering Control Module) continually monitors and adjusts steering efforts based on the torque sensor, motor position and HS-CAN (High Speed Controller Area Network) inputs to enhance the feel of the steering system. The level of steering assist is primarily based on vehicle speed. As vehicle speed increases, the amount of assist decreases to improve and enhance road feel at the steering wheel. As vehicle speed decreases, the amount of assist increases to ease vehicle maneuvering. Compensation is made to reduce the effect of pull or drift that can be experienced when driving on roads with a high degree of camber.
The PSCM (Power Steering Control Module) is self-monitoring and is capable of setting and storing DTCs (Diagnostic Trouble Codes). Depending on the DTC (Diagnostic Trouble Code) set, the PSCM (Power Steering Control Module) may enter a failure mode. REFER to Failure Modes. In addition, the PSCM (Power Steering Control Module) may send a request to the IPC (Instrument Panel Cluster) over the HS-CAN (High Speed Controller Area Network) to display a message in the message center, alerting the driver of a potential EPAS (Electronic Power Assist Steering) concern.
Failure Modes
When a DTC (Diagnostic Trouble Code) is present in the PSCM (Power Steering Control Module), the EPAS (Electronic Power Assist Steering) enters 1 of 2 modes of operation.
Reduced Steering Assist Mode
The EPAS (Electronic Power Assist Steering) enters a reduced steering assist mode to protect the internal components of the EPAS (Electronic Power Assist Steering) when a concern is detected by the PSCM (Power Steering Control Module), such as, low/high battery voltage or over-temperature concerns that are not considered to be a critical safety concern. The steering assistance sets to a default level and does not change with vehicle speed. This indicates that the steering assistance available for slow speed maneuvering is reduced, giving the steering a heavy feel. The assistance at high speed is greater than normal and can give the steering a lighter than normal feel.
Manual Steering Mode
The EPAS (Electronic Power Assist Steering) enters a manual steering mode (no electrical steering assistance is provided) when a concern that is considered to be a critical safety concern is detected or when a concern that caused the EPAS (Electronic Power Assist Steering) to enter reduced steering assist mode has been present for a predetermined number of key cycles. In manual steering mode, the vehicle has mechanical steering operation only, which gives steering operation a heavy feel.
Active Park Assist
Active park assist is an optional feature on this vehicle. REFER to Active Park Assist .