OBD codes stored by the electric power steering unit as faults and how they can be used to save diagnosing unnecessary parts.
Torque Sensor Faults
The torque sensor information is sent as a signal to the steering ECU as a sensor. The same types of fault codes (C-chassis codes) are created when the steering ECU detects an abnormal signal (inconsistent or missing) from the torque sensor. These types of codes can be caused by damage to the sensor itself or the wiring, or even a connector that has come loose over time. However, checking the live data first will determine if the sensor or the ECU is at fault.
Motor Current Faults
High resistance in the motor windings or a failing power stage inside the ECU are typical causes for motor current faults, logged as C-codes. As mentioned above, a reset of the ECU might clear the code temporarily, but if it comes back under load, it’s time to assess the motor and/or the ECU.
Voltage Supply Faults
Bearing in mind the high sensitivity of the new generation of electric steering racks to supply voltage, it is always worth checking battery health and earth straps on any occasions when strange codes are logged under steering related faults that have no relation to any malfunction of the rack.
CAN Bus Communication Errors
These are classified as U-codes, and indicate that the ECU steering system has lost contact with another vehicle control unit on the CAN network (e.g. engine management, or ABS). Do not immediately assume that the new rack is faulty – a network trace may reveal a different problem. As outlined in the diagnostic standards for automotive technicians, we follow a strict procedure for fault-finding of communication failures.
Calibration and Initialisation Faults
These types of codes are left after replacement of the steering rack or after a battery disconnect and need the steering angle sensor to be re-zeroed. A simple reset of the system is not enough here. A reinitialisation of the system via a diagnostic device which is able to carry out a calibration is necessary for example for electric parts of the steering rack. A useful reference for Electric Steering Racks is https://westernpowersteering.co.uk/steering-parts/electric-rack/.
Reading the freeze-frame data will allow you to see what happened when the fault occurred and will often rule out an electrical gremlin and confirm a component failure with an electric rack.
