Failure Modes

WARNING: This page is about a different car, the 2018 Ford EcoSport. However, it is still accessible from the selected car via links, so may be relevant.

When a DTC is present in the PSCM, the EPAS system enters 1 of 2 modes of operation.

Reduced Steering Assist Mode - The EPAS enters a reduced steering assist mode to protect the internal components of the EPAS system when a non-critical safety concern is detected by the PSCM, concerns such as low battery voltage, high battery voltage or over-temperature concerns are considered to be a non-critical safety concern. This reduced steering assist mode gives the steering operation a heavier than normal feel.

Manual Steering Mode - The EPAS system enters a manual steering mode (no electrical steering assistance is provided) when a concern considered to be a critical safety concern is detected. In manual steering mode, the vehicle has mechanical steering operation only which gives steering operation a heavy feel.

Component Description

EPAS Motor

The EPAS motor is a brushless type with a stator and 3 phases connected in star-delta. The rotor is a permanent magnet. The rotor position is detected by a total of 3 Hall-effect sensors and transmitted to the PSCM.

EPAS Steering Column

The EPAS steering column is an assembly consisting of a PSCM, a variable speed reversible motor, a steering shaft torque sensor and a reduction gearset, all of which are serviced as an assembly with the steering column.

PSCM

The PSCM is the ECU for the EPAS system. The module monitors all sensor inputs and HS-CAN messages relating to the EPAS system and directly controls the output of the EPAS motor.

Reduction Gearset

The reduction gearset consists of a worm gear which is permanently attached to the steering shaft and a worm shaft connected to the rotor of the EPAS motor.

Steering Shaft Torque Sensor

The steering torque sensor is mounted in the reduction gearset and is used by the PSCM to determine how much force is being used to turn the steering wheel and in which direction the steering wheel is being turned. This is accomplished using the electromagnetic induction between the sensor stator and the sensor rotor.