A technician is performing a diagnostic on a vehicle with Anti-lock Braking System (ABS) and Traction Control System (TCS). The client reports an intermittent 'hard pedal' sensation, usually after driving for a while, and the ABS/TCS warning lights occasionally illuminate. After checking conventional brake components, the technician connects a scan tool and retrieves Diagnostic Trouble Code (DTC) C0265: 'ECU Malfunction / Relay Circuit Failure'. Which of the following components is MOST likely at fault?
- AThe brake booster check valve.
- BThe master cylinder.
- CThe ABS hydraulic control unit (HCU) pump motor relay.
- DA wheel speed sensor.
Show answer & explanationAnswer & explanation
Correct answer: C. The ABS hydraulic control unit (HCU) pump motor relay.
DTC C0265 (ECU Malfunction / Relay Circuit Failure) specifically points to an issue with the ABS HCU's internal relay or its circuit, which controls the pump motor. A faulty relay can cause intermittent pump operation, leading to a hard pedal when ABS/TCS attempts to activate, and trigger the warning lights.
Why the other options are wrong
- A. A faulty brake booster check valve would cause a consistently hard pedal due to loss of vacuum assist, without specific ABS/TCS warning lights related to a relay circuit.
- B. A faulty master cylinder would typically cause a soft pedal or pedal sink, not an intermittent hard pedal with ABS/TCS lights.
- D. A faulty wheel speed sensor would typically cause ABS/TCS lights and possibly erratic ABS activation, but not usually an intermittent hard pedal sensation unless it prevents the HCU from releasing pressure, which is less common for C0265.
ABS HCU Pump Motor Relay
The ABS Hydraulic Control Unit (HCU) pump motor relay controls the activation of the pump motor, which is crucial for building and releasing hydraulic pressure during ABS and TCS operations. A failure in this relay can prevent proper ABS/TCS function, leading to warning lights and potentially affecting pedal feel.
- Controls ABS pump motor.
- Essential for ABS/TCS operation.
- Failure can cause warning lights.
- Can result in intermittent hard pedal.
Memory trick: C0265: The ABS pump's relay is in distress, making the pedal hard and a mess!