ASE H8 Preventive Maintenance & Inspection (Transit Bus) cheat sheet

49 CFR 396.17 requires a documented annual inspection every 12 months; the report is retained 14 months and the sticker records the due month and year.

DVIR rule: the driver completes a report each day the vehicle is operated; the carrier must certify each reported defect was repaired or is not safety-related, and reports are kept 3 months.

Brake-work gating rule: inspection, repair, and adjustment of brakes may be performed only by a qualified brake inspector under 49 CFR 396.25.

Whichever-comes-first rule: PM service is triggered by odometer, calendar date, or engine-hour meter, whichever limit is reached first.

Out-of-service decision rule: CVSA OOS defects (pushrod stroke over limit, 20% or more brakes defective, air loss beyond limits) stop the vehicle until repaired and re-inspected.

Record content rule: each repair entry ties unit number/VIN, odometer, defect found, cause, repair performed, parts used, technician ID, and date.

Road-test rule: after major brake, steering, or suspension repair, a road test is performed and documented before the bus returns to service.

Trend rule: the same defect recurring three times within 90 days flags a root-cause review rather than another component swap.

DEF specification: 32.5% urea by weight to ISO 22241; freezes near 12 F; store below 77 F out of sunlight; typical consumption is 1-3% of fuel volume.

DPF soot load is judged by differential backpressure or the aftertreatment model; active regeneration needs high exhaust temperature, so low-speed duty cycles require scheduled highway regen runs.

Air filter is serviced only when the restriction indicator reaches the manufacturer limit (commonly about 25 in H2O); check the element for tears and the housing for dust trails.

Cooling system: 50/50 mix protects to about -34 F; verify freeze point with a refractometer and additive levels with test strips; pressure test at cap rating and hold 5 minutes.

Belts: V-belt tension checked at about 1/2 in deflection on the longest span; the automatic tensioner pointer must sit inside the marked window; glazed or cracked belts are replaced.

Fuel system: water separator drained daily; after a filter change, prime the system and verify lift pump pressure, since air ingestion causes low power and hard starting.

Oil analysis at each PM: iron and lead wear trend, silicon (dirt ingress), sodium/potassium (coolant), fuel dilution, soot, and TBN.

Charge-air and exhaust: inspect CAC piping and boots for leaks, bellows for cracks, and hangers and sensor wiring for chafe.

Automatic transmission level check: engine running, transmission in Neutral, parking brake set, fluid at operating temperature, level within the HOT band.

Allison transmissions require TES 295 approved fluid; topping off with unapproved fluid alters friction characteristics and can cause clutch slip and shortened life.

Driveline: check each U-joint for radial play, missing snap rings, and rust-colored dust; lubricate slip yoke splines to spec; yokes must be in phase.

Differential: with the vehicle level, remove the fill plug and confirm lubricant is even with the bottom of the hole; inspect the magnetic plug for chips and abrasive paste.

Leak rule: a wet oil trail from a pinion, axle, or wheel seal is a defect; a joint that only seeps is monitored, one that drips is repaired.

Vibration diagnosis: check driveshaft runout at the center bearing, missing balance weights, and yoke phasing before condemning the transmission or differential.

Retarder: verify operation, inspect cooler lines and hoses for chafe, and confirm coolant level and chemistry because retarder use adds heat load to the cooling system.

Governor cut-out is typically 100-125 psi per vehicle spec, with cut-in about 20-25 psi lower; compressor build from 85 to 100 psi at fast idle must occur within 45 seconds.

Low-air warning buzzer and light must activate by 60 psi; spring (parking) brakes apply between roughly 20 and 45 psi.

Static leak test: fully charged system, engine off, brakes applied, pressure loss must not exceed 3 psi per minute on a single vehicle.

Pushrod stroke is measured at 90-100 psi application and compared to the chamber limit; a piggyback 30/30 clamp-type chamber limits near 2 1/2 in.

Automatic slack adjusters must not be repeatedly hand-adjusted to mask over-stroke; over-stroke means the adjuster or foundation brake needs repair.

Drum and lining: bonded lining is condemned near 1/4 in; rivet heads must not be within 1/16 in of the friction surface; drums are checked for cracks, heat checks, and maximum diameter.

Air dryer: desiccant and purge valve serviced on interval; moisture found in any reservoir after a normal day indicates dryer or drain failure.

Wheel end: hub oil level, seal leaks, bearing play of 0.001-0.010 in, ABS tone ring and sensor gap, and fastener torque with a calibrated wrench.

Tread depth: steer axle minimum 4/32 in, all other axles 2/32 in; retreaded or recapped tires are not permitted on the steer axle of a bus.

Pressure rule: check cold with a calibrated gauge and adjust to placard; never bleed hot tires; duals are matched within the manufacturer's diameter tolerance.

Free play: steering wheel movement before the tires respond must not exceed 10 degrees, about 2 in at the rim of a 20-in wheel.

Air suspension: measure ride height at the specified frame-to-axle points before alignment; a sagging corner points to a bag, height valve, or linkage.

Spring and hardware: check for cracks, missing or shifted leaves, worn bushings, and U-bolt torque; broken leaves or loose U-bolts are out of service.

Linkage: tie rod, drag link, kingpin, and pitman arm play checked while a helper rocks the wheel; missing cotter pins and cracked arms are defects.

Wheel fasteners: torque with a calibrated wrench and inspect indicators; rust streaks or shiny threads at a nut indicate a loose fastener.

State of charge: 12.6 V = 100%, 12.4 V about 75%, 12.2 V about 50%; recharge below 12.4 V before load testing.

Load test at half the CCA rating or with a conductance tester; a battery falling below 9.6 V under load at 70 F fails.

Charging: 13.8-14.5 V on 12 V systems and about 27.5-28.5 V on 24 V systems; a 0.5 V difference between alternator output and battery terminal indicates cable or connection loss.

Voltage drop limit: 0.5 V total in a 12 V cranking circuit, 1.0 V in a 24 V circuit; test under load, not open circuit.

Lighting: turn signals flash 60-120 times per minute; clearance, marker, stop, tail, and backup lamps must all operate; sealed LED assemblies are replaced as units.

Parasitic draw: with loads off, doors closed, and modules asleep, current should stay under the manufacturer limit, typically about 50 mA.

Battery service: clean and torque terminals, verify hold-downs and covered terminals, confirm venting, and inspect cable chafe at frame pass-throughs.

Refrigerant: R-134a with PAG oil; recovery and recycling with certified equipment is mandatory under EPA Section 608, and venting to atmosphere is prohibited.

Performance check: center vent temperature typically 35-45 F below ambient, with high-side and low-side pressures matching the service chart.

Airflow: return-air and fresh-air filters, blower operation at every speed, evaporator coil cleanliness, and a clear condensate drain.

Heat and defrost: coolant control valve travel, booster pump operation, blower output, and full defrost coverage of the windshield.

Exits: push-out windows, roof hatch, and rear door must open with normal force, alarms must sound, and interior and exterior exit markings must be legible.

Fire equipment: extinguisher gauge in the green, seal intact, bracket secure, inspection tag current; engine-compartment suppression nozzles and sensors clean.

Passenger area: seats and stanchions secure, floor and stepwell sound, stop-request and PA working, destination sign legible, camera lenses clean.

Wheelchair securement: four tiedown points plus lap and shoulder belt present, operable, and free of fraying or bent hardware.

Engine oil: API CK-4 or CJ-4; viscosity chosen by ambient (15W-40 common above 0 F, 5W-40 for cold starts); never mix viscosity grades to top off.

Sampling: draw mid-drain from a warm, well-mixed sump into a clean bottle and record miles and hours on the label so trends align with the service interval.

Coolant: 50/50 premix with freeze point near -34 F; conventional coolant requires nitrite/SCA within the test-strip range, while OAT coolant must not be dosed with SCA.

Fluid identity rule: 75W-90 or 80W-90 gear lube, TES 295 ATF, and the specified power-steering fluid are not interchangeable; the wrong fluid damages components.

Filter rule: oil, fuel, air, transmission, and coolant filters each follow their own interval; an additive-release coolant filter is not a substitute for testing coolant chemistry.

Safety: chock wheels, lock out and tag air and electrical energy, wear PPE, keep the eyewash station stocked, keep SDS sheets accessible, and never use compressed air on skin.

Environmental: used oil, filters, coolant, and refrigerant are recycled or reclaimed; a spill kit is on hand and floor drains are protected.