CDL Air Brakes TestAir Brake System PartsMedium
A technician is diagnosing an issue where the stop lights on a commercial vehicle with air brakes are not illuminating when the service brake pedal is pressed. Which specific component should be inspected first?
- AThe front brake limiting valve.
- BThe low air pressure warning buzzer.
- CThe stop light switch.
- DThe air compressor governor.
Show answer & explanationAnswer & explanation
Correct answer: C. The stop light switch.
The stop light switch is specifically designed to activate the stop lights when the service brakes are applied. If the stop lights are not working despite the pedal being pressed, this switch is the most direct and likely cause of the problem.
Why the other options are wrong
- A. The front brake limiting valve adjusts front brake pressure, not stop light activation.
- B. The low air pressure warning buzzer alerts for low air, unrelated to stop light function.
- D. The air compressor governor controls air pressure, not brake lights.
Stop Light Switch
The stop light switch is an electrical switch that detects when the service brake pedal is pressed and sends a signal to illuminate the vehicle's stop lights.
- Activates brake lights.
- Located near the brake pedal or air lines.
- Crucial for vehicle safety and communication.
Memory trick: No lights? Check the switch that 'sees' the brake.