Vehicle Systems, Brakes, and Pre-Trip Inspection Knowledge
Vehicle Systems, Brakes, and Pre-Trip Inspection Knowledge
This domain tests air and hydraulic brake operation, ABS, tires, suspension, electrical, and exhaust systems, plus the inspection tests that prove they work. Numbers matter here.
Core rules
- For air brakes, build pressure from 85 to 100 psi within 45 seconds. With the engine off and parking brake released, static leakage should be less than 2 psi per minute. With the brakes applied, leakage should be less than 3 psi per minute.
- The low-pressure warning must activate before pressure falls below 60 psi. The spring brakes should set between 20 and 45 psi. Drain air tanks daily to remove moisture and oil.
- Check tire tread depth, sidewalls, and inflation; look for cracked rims, loose lug nuts, broken springs, and air leaks. An ABS lamp that stays on indicates a fault; the vehicle may still have normal braking, but the problem must be repaired.
Worked example
With the engine off and parking brake released, a driver sees a 1-psi drop in one minute and then a 2-psi drop in one minute with the brakes applied. Both results pass: static loss is under 2 psi and applied loss is under 3 psi. Reasoning: the driver must run both tests separately and compare each to its own threshold, not to a single number.
Traps that cost marks
Mixing the 2-psi and 3-psi leak limits; skipping tank drains; ignoring a steady ABS lamp; and accepting a low-pressure warning that sounds only after pressure is already below 60 psi.