CDL Air Brakes TestAir Brake System PartsMedium
A technician is troubleshooting a commercial vehicle's air brake system. They observe that the service brakes apply correctly, but the stop lights do not illuminate when the brake pedal is pressed. Where should the technician first investigate the issue?
- AThe brake chamber diaphragms.
- BThe stop light switch.
- CThe air compressor governor.
- DThe low air pressure warning switch.
Show answer & explanationAnswer & explanation
Correct answer: B. The stop light switch.
The stop light switch is specifically designed to activate the vehicle's stop lights when the service brakes are applied. If the brakes work but the lights don't, the switch is the most direct point of failure.
Why the other options are wrong
- A. Brake chamber diaphragms are part of the mechanical braking system; if they were faulty, the service brakes themselves would not apply correctly.
- C. The governor controls air pressure build-up, not stop light activation.
- D. The low air pressure warning switch monitors system pressure and activates a warning, unrelated to stop lights during normal braking.
Stop Light Switch
A pressure-activated electrical switch in an air brake system that illuminates the vehicle's stop lights when the service brakes are applied.
- Ensures other drivers are aware of braking.
- Located near the brake pedal or in the air line to the service brakes.
- Essential for safety and legal compliance.
Memory trick: Brake light switch, a bright safety stitch!