CDL Air Brakes TestAir Brake System PartsMedium
A technician is diagnosing an issue where a commercial vehicle's spring brakes are not releasing properly, even with adequate air pressure in the system. Which component is the most likely culprit?
- AThe foot brake valve.
- BThe parking brake control valve.
- CThe anti-lock braking system (ABS) module.
- DThe air compressor governor.
Show answer & explanationAnswer & explanation
Correct answer: B. The parking brake control valve.
The parking brake control valve (often a push-pull knob) is responsible for controlling the air pressure to the spring brakes. When pushed in, it sends air to release the spring brakes; if it malfunctions, air may not reach the spring brakes, preventing their release.
Why the other options are wrong
- A. The foot brake valve controls the service brakes, not the parking (spring) brakes.
- C. The ABS module manages wheel speed during braking and does not directly control the release of spring brakes.
- D. The air compressor governor controls the compressor's cut-in/cut-out, not the release of spring brakes.
Parking Brake Control Valve
A valve, typically a push-pull knob on the dashboard, that controls the air pressure sent to the spring brakes to release or apply them.
- Pushing in releases the spring brakes by sending air pressure.
- Pulling out applies the spring brakes by exhausting air pressure.
- Integral to parking and emergency brake functions.
- Malfunctions can prevent spring brake release or application.
Memory trick: Stuck brakes, big frustration, check the knob for proper operation.