Vehicle Inspection, Braking, and Antilock Brake Systems
Domain 4 tests pre-trip inspection of school-bus-specific equipment and air-brake/ABS knowledge. Expect questions on warning devices, emergency exits, brake tests, and what ABS can and cannot do.
Pre-trip essentials
- Check the eight-light system, stop arm, crossing gate, and all turn/brake lights.
- Verify emergency exits open and close, the fire extinguisher is charged and mounted, the first aid kit is stocked, and three reflective triangles are aboard.
- Check tires, belts, hoses, fluids, seat belts, and the handrail.
Air-brake tests
- Static leak test: fully charged, engine off; pressure loss should not exceed 2 psi per minute for a single vehicle.
- Applied leak test: hold the brake; loss should not exceed 3 psi per minute.
- Low-pressure warning must activate before pressure falls below 60 psi.
- Spring brakes should set between 20 and 45 psi.
- Perform a service-brake stop from about 20 mph and check for pulling or delay.
ABS
ABS keeps wheels from locking and helps maintain steering control, but it does not shorten stopping distance on gravel and is not a substitute for following distance. Press and hold the brake; do not pump. If the ABS lamp stays on, the bus still has normal brakes but should be reported.
Worked example
During the static leak test, pressure drops 4 psi in one minute. The driver does not sign the inspection as passed; the loss exceeds the 2 psi limit, so the bus is removed from service until the leak is repaired. The driver also notes a low-pressure warning that did not sound until 50 psi, another defect.
Traps
- Skipping the applied leak test.
- Treating ABS as a guarantee of a shorter stop.
- Missing a stop arm or emergency-exit defect on the pre-trip.
- Ignoring a warning that activates too late.