Automobile & Light Truck Certification Test A5 BrakesAnti-lock Brake System (ABS) Diagnosis and RepairMedium
A technician is diagnosing an ABS warning light on a vehicle that uses an integral ABS design (pump and control module combined). The scan tool indicates a C0110 fault code: 'Pump Motor Circuit Malfunction'. Which of the following components is MOST likely to be the source of this fault if all wiring and power/ground supplies to the ABS module test good?
- AA low brake fluid level in the master cylinder reservoir
- BA faulty wheel speed sensor
- CAn internal fault within the ABS hydraulic control unit (HCU) pump motor assembly
- DA stuck open ABS solenoid valve
Show answer & explanationAnswer & explanation
Correct answer: C. An internal fault within the ABS hydraulic control unit (HCU) pump motor assembly
If the C0110 fault code (Pump Motor Circuit Malfunction) is present and the external wiring and power/ground supplies to the entire ABS module are verified as good, the fault must lie within the integral ABS unit itself, most commonly the pump motor assembly.
Why the other options are wrong
- A. Low brake fluid level would cause a brake system warning light, not typically an ABS C0110 code, unless it leads to other hydraulic issues.
- B. A faulty wheel speed sensor would generate a C00xx code specific to the sensor, not a C0110 pump motor code.
- D. A stuck open ABS solenoid valve would typically cause a C0121 or similar code related to valve performance, not a pump motor circuit malfunction.
ABS Pump Motor Circuit Malfunction
A fault code (e.g., C0110) indicating an issue with the electrical circuit or internal components of the ABS hydraulic pump motor.
- Often points to problem within the ABS HCU (integral design).
- Requires verifying external power/ground before internal diagnosis.
- Can prevent ABS/ESC from functioning correctly.
Memory trick: C0110: The Pump Motor is a NO-GO!