ASE A4 Suspension and SteeringSteering System Diagnosis and RepairHard
A vehicle equipped with an electric power steering (EPS) system develops a sudden loss of power assist. The dashboard displays a 'Power Steering Malfunction' warning light. Using a scan tool, a technician retrieves Diagnostic Trouble Code (DTC) C0550. What is the MOST likely issue indicated by this DTC and symptom combination?
- AA disconnected steering angle sensor.
- BA fault in the EPS control module or motor.
- CLow power steering fluid level.
- DA mechanical binding in the steering rack.
Show answer & explanationAnswer & explanation
Correct answer: B. A fault in the EPS control module or motor.
A sudden loss of power assist with a 'Power Steering Malfunction' light and a C0550 DTC strongly points to a fault within the EPS control module or the electric motor itself. C0550 typically indicates an internal control module fault or a motor circuit issue, not mechanical binding, fluid level (as EPS is fluidless), or just a sensor issue.
Why the other options are wrong
- A. A disconnected steering angle sensor would typically trigger a specific DTC related to that sensor (e.g., C0460-C0465 range) and might cause incorrect assist rather than a complete loss with a C0550 module/motor fault.
- C. Electric power steering systems do not use hydraulic fluid, so low fluid level is not applicable.
- D. Mechanical binding would cause hard steering but might not immediately trigger a control module DTC like C0550, and the system would likely try to assist against the binding.
Electric Power Steering (EPS) Diagnostics
Diagnosing EPS systems involves interpreting DTCs, understanding system components, and recognizing the absence of hydraulic fluid.
- EPS systems use electric motors for assist, not hydraulic pumps.
- DTCs are crucial for pinpointing electronic faults.
- C0550 often indicates internal module or motor circuit issues.
- Loss of assist and warning lights are common failure symptoms.
Memory trick: Electric Problems Elicit Error Codes.