Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A technician is performing a brake inspection on a vehicle with a complaint of a 'soft' or 'spongy' brake pedal. The master cylinder is full, and there are no external leaks. After bleeding the system at all four wheels using the conventional method, the pedal feel improves slightly but is still not firm. The vehicle is equipped with an Anti-lock Braking System (ABS). What should be the NEXT step in diagnosing and repairing this issue?
- AInspect the brake booster for proper operation.
- BPerform an automated ABS bleed procedure.
- CReplace the master cylinder.
- DReplace all brake hoses.
Show answer & explanationAnswer & explanation
Correct answer: B. Perform an automated ABS bleed procedure.
If a conventional bleed does not fully resolve a spongy pedal and no external leaks are present, air may be trapped in the ABS hydraulic control unit (HCU). Many ABS systems require a scan tool to actuate the ABS solenoids and pump, forcing air out of the HCU during an automated bleed procedure.
Why the other options are wrong
- A. A faulty brake booster typically causes a hard pedal, not a soft or spongy one.
- C. While a faulty master cylinder can cause a soft pedal, it's typically ruled out if no external leaks are present and an automated ABS bleed hasn't been attempted.
- D. Replacing all brake hoses is a significant and often unnecessary step if no specific hose damage or swelling is identified as the cause of the soft pedal.
ABS Automated Bleed
A procedure using a scan tool to cycle the solenoids and pump within the ABS hydraulic control unit (HCU) to purge trapped air that cannot be removed by conventional bleeding methods.
- Required for many ABS systems after repair or air ingress.
- Uses a scan tool to activate ABS components.
- Removes air trapped in the HCU.
Memory trick: Soft pedal, check for air, then ABS, then bigger repair.