Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A customer complains that their vehicle's electric parking brake (EPB) engages and disengages slowly, and sometimes fails to release fully, causing a slight drag. There are no warning lights on the dashboard. What is the MOST likely cause of this issue?
- ACorrosion or binding in the EPB motor/actuator assembly.
- BA low brake fluid level.
- CAn incorrectly adjusted service brake pedal.
- DA faulty ABS wheel speed sensor.
Show answer & explanationAnswer & explanation
Correct answer: A. Corrosion or binding in the EPB motor/actuator assembly.
Electric parking brakes use an electric motor to actuate the parking brake mechanism directly at the caliper or hub. Over time, corrosion, dirt, or internal wear can cause the motor or its mechanical linkage (actuator) to bind or operate slowly, leading to delayed engagement/disengagement and potential dragging.
Why the other options are wrong
- B. Low brake fluid primarily affects the hydraulic service brakes, not the independent electric parking brake.
- C. An incorrectly adjusted service brake pedal affects hydraulic brake feel and engagement, not the independent electric parking brake.
- D. A faulty ABS wheel speed sensor would typically cause ABS/Traction Control warning lights and affect those systems, not directly the EPB's mechanical operation.
EPB Actuator Binding
Corrosion, dirt, or internal wear within the electric parking brake motor or actuator assembly can cause it to bind, leading to slow engagement/disengagement, partial release, or dragging.
- EPB is an independent system.
- Mechanical binding affects operation.
- Can occur without dashboard warning lights.
Memory trick: EPB slow, check the motor, then the cable, then the code.