Emergency Procedures and Malfunction Response
Emergency Procedures and Malfunction Response
This domain tests what to do when air pressure is lost, brakes fade, or a spring brake or trailer emergency system activates. The safe answer is almost always: stop safely, secure the vehicle, and do not continue until repaired.
Core rules
- If the low-pressure warning activates, stop as soon as it is safe. Pressure may continue falling; spring brakes can apply automatically between 20 and 45 psi. Do not try to reach the shop with a known air leak.
- If service brakes fail, use engine braking, downshift progressively, and apply the parking/emergency brake gradually. A sudden full spring-brake application at speed can lock wheels and cause a skid.
- If a trailer supply line separates or the tractor protection valve closes, the trailer emergency brakes should apply. Stop and check the coupling and lines; do not bypass the protection valve.
- Brake fade from overheated foundation brakes requires stopping to cool. Downshift and use engine braking; do not continue at the same speed.
- A spring brake that will not release may need mechanical caging for movement out of danger or towing. Caging is not a repair and not a normal driving mode.
Worked example
On a highway, the warning buzzer sounds just above 60 psi and the gauge is falling. You signal, move to the shoulder, and stop while steering is still normal. You do not wait for the spring brakes to set at 30 psi, because that could happen in a travel lane. After stopping, you set the parking brake, chock the wheels, and inspect for a broken line or open drain.
Traps
Do not pump the brakes to “build pressure” when the compressor has failed; pumping only lowers pressure faster. Do not cage spring brakes and drive normally. Do not ignore a warning that activates at or above 60 psi; it means pressure is already low and may keep falling.