Steering (Operation): Description and operation (page 2 of 3)

EPAS electrical operation

EPAS ECU

1. Torque sensor
2. Main Potentiometer
3. Sub Potentiometer
4. Speed sensor
5. Engine revolution sensor
6. Ignition switch supply
7. Battery supply
8. Earth
9. Interface

The torque sensor has two potentiometers. The potentiometers share a power supply and earth connection from the ECU and operate in the same direction. One potentiometer provides the torque data and the other potentiometer acts as a fault monitor. The ECU checks the output from each potentiometer and will illuminate the EPAS warning lamp and suspend power assistance whilst the fault is present.

10. Main control computer
11. Fail safe relay
12. Motor drive circuit
13. Current control circuit
14. Clutch drive circuit
15. Motor
16. Clutch
17. Warning lamp

When the ignition is switched on, the EPAS ECU performs a start-up (diagnostic) check procedure. The ECU illuminates the EPAS fault warning lamp in the instrument pack. The lamp will remain illuminated until the engine is started and the ECU receives an engine running signal from the crankshaft position (CKP) sensor.