The pre-trip inspection is the single most-failed component of the CDL skills test. Examiners across all 50 states report that more candidates lose points here than on basic control or the on-road test combined. The good news: it's pure memorization plus practice. Master a consistent inspection routine and you'll pass every time.
Engine compartment
Belts and hoses (no cracks, frays, or leaks); leaks under the engine; coolant level (sight glass, no removal of pressurized cap when hot); engine oil level (dipstick); power-steering fluid; windshield washer fluid; air compressor (mounted securely, belts tight if belt-driven); alternator (mounted securely, belts tight, wiring intact); water pump (no leaks); steering box and hoses (no leaks, mounted securely); steering linkage (no missing parts, no broken welds, no excessive play).
In-cab
Seat belt; mirrors (clean, properly adjusted); windshield (no cracks in driver's view); horn (city and air horns both); wipers and washers; heater/defroster; gauges all functional (oil pressure, water temp, ammeter/voltmeter, air pressure); emergency equipment (3 reflective triangles, fire extinguisher with current inspection, spare fuses unless equipped with circuit breakers); steering wheel play (no more than 10 degrees / 2 inches at the rim).
Air brake check
This sub-component is critical: with engine off and key on, build pressure to governor cut-out (typically 120–140 psi); test compressor governor cut-in (drops to 100–125 psi); test air loss rate (less than 3 psi per minute single, 4 psi per minute combination, brakes off); test low-air warning (must come on at 60 psi or above); test spring brake activation (must engage between 20 and 45 psi); test service brakes (apply firmly, check for further air loss, listen for leaks).
Lights, walk-around, coupling, trailer
All exterior lights working (headlights high/low, turn signals front and back, brake lights, four-way flashers, tag light, marker lights, identification lights). Walk-around the vehicle checking tires (4/32 tread on steer axle, 2/32 elsewhere; no cuts, bulges, or sidewall damage; valve stems intact; lug nuts tight, no rust trails, no missing nuts). For combination vehicles: fifth wheel (mounting bolts, no cracks, properly greased, jaws closed around kingpin, locking lever locked, safety latch engaged); air and electrical lines (no cracks, no leaks, supported off catwalk).
For full memorization aids, see our General Knowledge study guide and your state's official CDL handbook, which lists inspection items in the order your examiner expects to hear them.