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 needs to be connected to battery voltage at the hot at all times input and at the ignition/run input to the PSCM (Power Steering Control Module). In addition, the system must communicate with other modules over the HS-CAN (High Speed Controller Area Network). The PSCM (Power Steering Control Module) must receive the power mode signal from the BCM (Body Control Module) in order to be set into operation mode.
The main input for calculating the level of EPAS (Electronic Power Assist Steering) assist is the torque sensor signal. Vehicle speed is also taken into consideration in order to achieve the vehicle speed dependent steering assist characteristic.
The EPAS (Electronic Power Assist Steering) gear uses a reversible motor to apply the steering assist. 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 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. 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. Also compensation for the impact of wheel imbalance on steering feel is made up to a predetermined threshold.
The steering torque sensor senses the torque at the steering wheel. It is hard wired to the PSCM (Power Steering Control Module) and works by measuring the relative rotation between an input and output shaft which are connected by a torsion bar. The torque sensor sends out 2 PWM (Pulse Width Modulated) signals which allows a channel to channel cross-check and an accurate correction of the neutral point.
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) to display a message in the message center, alerting the driver of a potential EPAS (Electronic Power Assist Steering) concern. The warning message is sent over the HS-CAN (High Speed Controller Area Network) to the BCM (Body Control Module) where it is converted to a MS-CAN (Medium Speed Controller Area Network) message and forwarded on to the IPC (Instrument Panel Cluster) over the MS-CAN (Medium Speed Controller Area Network).
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 .