Steering (Diagnostics): Description and operation

The EPAS ECU uses this information to calculate the ideal level of power assistance required for the driving conditions and applies a current of the applicable amperage to the electric motor mounted on the steering column. The electric motor applies the required torque to the steering shaft via a worm gear.

EPAS ECU

The EPAS ECU is located above the glove box, behind the fascia. The ECU is rubber mounted to a bracket on the front bulkhead and is secured by a bracket with two bolts to the body cross tube.

The EPAS system incorporates fail-safe devices which cause it to revert to conventional manual steering in the event of a system failure. The EPAS ECU integral fault monitor sends a signal to the electromagnetic clutch which disconnects the motor mechanical drive to the column. Fault codes are stored in the EPAS ECU memory, for identification by TestBook.

If a fault occurs, the EPAS ECU illuminates the EPAS warning lamp in the instrument pack. If, when the ignition is switched off and back on again, the fault is no longer present, the ECU will not illuminate the fault lamp after the engine is started. The ECU stores a fault code for the fault. If the fault does not re-occur in the next twenty ignition cycles, the ECU will erase the fault code.

Field Effect Transistors (FET’s) in the ECU protect the system from overload. If excessive use or component failure causes the motor to overheat, the FETS will become hot. As the temperature increases, the FET’s and the EPAS ECU gradually decrease the level of steering assistance provided. As the system cools the level of steering assistance is progressively reinstated.

Permanent battery voltage is supplied to the EPAS ECU via a dedicated EPAS 40A fuse which is located remotely adjacent to the underbonnet fusebox.

Two multiplugs provide input and output connections to and from the ECU. The following tables show the harness connector pin numbers and input/output information.

Instrument pack

The EPAS ECU informs the driver of any malfunctions via a warning lamp on the instrument pack. The warning lamp receives a 12V supply from fuse 1 in the passenger compartment fusebox when the ignition is in position II. The EPAS ECU connects the warning lamp to earth when fault warning lamp illumination is required.

1. EPAS warning lamp

Diagnostics

A diagnostic socket allows the exchange of information between the EPAS ECU and TestBook. The diagnostic socket is located in the passenger compartment fusebox which is below the fascia on the driver’s side.

The EPAS ECU monitors inputs and outputs relating to the EPAS system. If a fault is detected, a code applicable to that fault is stored in a fault log in the ECU.