EPAS (MG) - System Overview
Electric Power Assisted Steering (EPAS). This is a system which is based on the conventional rack and pinion steering setup. It differs from the conventional in that it has an electric motor mounted on the steering column which applies a variable force to the steering shaft via a worm gear. This variable force, which is the power assistance, is dependant on the vehicle speed and drivers’ steering effort.
The EPAS ECU calculates the required amount of assistance to apply (by the motor) by monitoring driver input via torque sensors on the steering column, engine speed and vehicle speed. Power assistance should be most evident at low speeds. Faults in the system are indicated by the EPAS ECU via a warning light on the instrument panel.
SM094 - EPAS (MG) - System Help file
Version 1.22

EPAS (MG) - Known Fitments
Vehicle makes, models and variants known or believed to be using this vehicle system, required diagnostic lead and degree of known compatibility.

Vehicle Make Vehicle Model Vehicle Variant Diagnostic Lead
MG MGF All with Electronic Power Steering Black OBDII Lead
MG TF All with Electronic Power Steering Black OBDII Lead

EPAS (MG) - Physical Details

EPAS - Pin Outs
Details of the pin usage for the ECU connector(s).

BLACK CONNECTOR  
1 Feed back
2 Instrument pack
3 Not used
4 Sensor Torque
5 Sensor Torque
6 Sensor Torque
7 Road Speed
8 Ignition
9 Feed back
10-11 Not Used
12 Sensor Torque
13 Sensor Torque
14 Sensor Torque
15 Engine Speed
16 Diagnostics (to Pin 1 of OBD)

Natural  
1 Permanent Battery power
2 Motor
3 Earth
4 Motor

SM094 - EPAS (MG) - Diagnostic Capabilities (Read Fault Codes)
Reads the fault code memory. The ECU can self detect 16 different problems with itself, its wiring and its associated sensors, storing the respective code if it detects any malfunction or reading outside of predefined acceptable limits. Not all stored faults may cause the fault warning lamp to illuminate.

SM094 - EPAS (MG) - Diagnostic Capabilities (Clear Fault Codes)
This function clears the fault code memory.

SM094 - EPAS (MG) - Diagnostic Capabilities (Settings)
Stored information which can be read from the ECU. Read settings can also be stored as a standard HTML page for reference. Please note that some values may be read only due to the fact that they are supplied from the ECU's ROM or are internally calculated.
  • EPAS Version: The internal version information displayed exactly as it is stored in the ECU. Valid versions are 1 and 2.

SM094 - EPAS (MG) - Diagnostic Capabilities (Inputs)
Realtime live display of the information the electronic control unit of the selected vehicle system is currently deriving from its input sensors.

In order to read the real values for these inputs, engine idling and fully warm, neutral selected and handbrake on are required.
  • Sub torque (V):This is the voltage supplied to the main torque sensor. Expected values should be in the range 1V to 4V, normal value being around 2.5V.
  • Sub torque (Nm):The main torque sensor is mounted together with the sub torque sensor on the steering column and measure the amount of torque that is applied to the steering wheel. The sensor in conjunction with the sub torque sensor is used as a means of detecting when steering assistance is required. If the difference in the values becomes greater then 6% then it is considered that there is a fault and EPAS assistance is withdrawn.
  • Sub torque (V):This is the voltage supplied to the sub torque sensor. Expected values should be in the range 1V to 4V, normal value being around 2.5V.
  • Sub torque (Nm):The sub torque sensor is mounted together with the main torque sensor on the steering column and measure the amount of torque that is applied to the steering wheel. The sensor in conjunction with the main torque sensor is used as a means of detecting when steering assistance is required. If the difference in the values becomes greater then 6% then it is considered that there is a fault and EPAS assistance is withdrawn.
  • Torque sensor supply:This is the voltage supplied to the torque sensor. Expected values should be in the range 8.4V to 13.7V.
  • Target current (A):Target current value calculated by the ECU. This value is compared with the observed current. The values vary depending on the amount of torque applied to the steering wheel and the level of assistance the motor is currently providing. Values should range from 0.0A to a maximum of 39.5A
  • Observed Current (A):This is the current observed. This value is compared with the target current calculated by the ECU. The values vary depending on the amount of torque applied to the steering wheel and the level of assistance the motor is currently providing. Values should range from 0.0A to a maximum of 39.5A
  • EPAS assistance (%):This displays the amount of assistance the EPAS motor is applying.
  • Vehicle speed (Km/h):This is the vehicle speed in km/h. The signal is supplied to the EPAS ECU from a reed switch that is located in the speedometer assembly and is used to determine how much assistance should be applied to the steering column. This signal will only be present if the speedometer is functioning correctly.
  • Vehicle speed (mph):This is the vehicle speed in mph.
  • Engine speed (RPM):This is the engine speed signal, supplied to the EPAS ECU from the engine management ECU. In the case of the vehicle speed signal failing the engine speed is used as a fail safe to shut down the EPAS system.