Vehicle condition and air brake system checks
Prove the air system, do not assume it
Air brakes are the highest-risk system on a Class 2 bus, so the exam expects a sequence, not isolated facts. With the engine running at fast idle, pressure should climb from about 85 psi (587 kPa) to 100 psi (690 kPa) within two minutes. Note where the governor cuts out and cuts back in. Shut the engine off and watch for leakage: with brakes released a single unit should lose no more than roughly 3 psi per minute; with the pedal fully applied, no more than roughly 4 psi per minute. Confirm the low-pressure warning sounds before pressure falls below 60 psi, and that spring brakes apply automatically at about 20 to 45 psi.
Then check the mechanical side: with brakes applied, measure pushrod travel against the manufacturer's limit and watch slack adjusters for excessive free play. Drain the air tanks daily to remove moisture; oil or coolant in the air means compressor trouble. Condition checks extend beyond brakes - coolant level, belts, oil, power steering, tires, and suspension all belong in the same walk-around.
Traps: candidates confuse cut-in with cut-out, forget the engine must be off for a leakage test, or think a low-air warning replaces spring brakes. Remember that if you must fan the pedal to hold pressure, the bus is out of service - brake fade from heat is a failure, not a nuisance.
Rule of thumb
Build, hold, lose, warn, apply: build-up time, leak-down rate, low-pressure warning, spring brake application. If any stage fails, park it.