Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A customer complains that their vehicle's electric parking brake (EPB) will not disengage after being applied. The technician connects a scan tool and finds no diagnostic trouble codes (DTCs). Which of the following is the MOST likely cause?
- AA seized electric parking brake caliper actuator.
- BLow brake fluid level in the master cylinder reservoir.
- CA faulty wheel speed sensor causing an ABS malfunction.
- DContaminated brake fluid requiring a system flush.
Show answer & explanationAnswer & explanation
Correct answer: A. A seized electric parking brake caliper actuator.
If the electric parking brake actuator seizes, it can prevent the parking brake from disengaging, even if there are no DTCs because the control module is commanding disengagement but the mechanical component is stuck. The other options are less likely to directly cause a non-disengaging EPB without generating DTCs or affecting service brakes more broadly.
Why the other options are wrong
- B. Low brake fluid primarily affects hydraulic service brakes and would not typically prevent an electric parking brake from disengaging.
- C. A faulty wheel speed sensor would likely cause ABS/Traction Control DTCs and might prevent EPB operation, but less likely to prevent disengagement specifically without other symptoms or codes.
- D. Contaminated brake fluid would affect the entire hydraulic system and is not directly related to the mechanical disengagement of an electric parking brake actuator.
Electric Parking Brake (EPB) Actuator Seizure
A mechanical failure where the electric motor and gearing mechanism within the EPB caliper actuator becomes stuck, preventing the parking brake from engaging or disengaging.
- Can occur due to corrosion, internal component failure, or debris.
- Often results in the parking brake being stuck ON or OFF.
- May or may not trigger diagnostic trouble codes (DTCs) immediately.
Memory trick: Electric Brakes Stuck, Actuator's the Suspect.