Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairHard
A technician is performing a brake flush on a vehicle with ABS. After completing the flush using a pressure bleeder, the technician notices that the brake pedal still feels somewhat soft and spongy. No external leaks are present. What is the MOST probable next step?
- AReplace the master cylinder.
- BRe-bleed the entire system manually.
- CPerform an ABS automated bleed procedure using a scan tool.
- DInspect the brake hoses for internal restriction.
Show answer & explanationAnswer & explanation
Correct answer: C. Perform an ABS automated bleed procedure using a scan tool.
Many modern ABS systems have internal valves and accumulators that can trap air. A standard pressure bleed may not remove all air from these components. An automated bleed procedure, activated with a scan tool, cycles these components to release trapped air, which is often necessary to achieve a firm pedal after a flush or repair.
Why the other options are wrong
- A. Replacing the master cylinder without addressing potential trapped air in the ABS module would be premature and likely ineffective.
- B. Manual bleeding might not reach trapped air within the ABS module.
- D. Internal hose restriction would typically cause a drag or reduced braking, not a generally soft pedal after a flush.
ABS Automated Bleed
A specialized procedure using a scan tool to cycle the ABS pump and valves to purge air from the ABS hydraulic control unit.
- Required after some brake system repairs or flushes.
- Necessary to remove trapped air from ABS module.
- Cannot be performed with conventional bleeding methods.
Memory trick: ABS hides air, a scan tool clears it there.