ASE H8 Preventive Maintenance & Inspection (Transit Bus) key terms

A written list of components and conditions checked at scheduled intervals to catch wear, leaks, and safety defects before they cause a roadside failure.

A document that authorizes and records maintenance work, including the vehicle, reported problem, assigned technician, parts used, labor, and completion status.

A fault found during inspection that does not require immediate repair but is recorded, scheduled, and tracked until it is corrected.

Laboratory testing of engine oil for wear metals, contaminants, viscosity, and additive depletion; results guide oil drain intervals and reveal internal wear trends.

The temperature at which engine coolant begins to freeze, checked with a refractometer or hydrometer to confirm the antifreeze mixture protects the engine in cold weather.

A check of the accessory drive belt for cracks, glazing, fraying, missing ribs, and correct tension or automatic tensioner travel before failure.

A heat exchanger that cools compressed intake air from the turbocharger before it enters the engine, increasing air density and reducing thermal stress.

A high-temperature process that burns accumulated soot from the exhaust filter; passive regeneration occurs during normal operation, while active regeneration uses extra fuel or heat.

A procedure that verifies automatic transmission fluid is at the specified level and condition with the engine running and transmission at the manufacturer's stated temperature.

The correct alignment of universal joint yokes on a driveshaft so that rotational speed variations cancel, preventing vibration and premature joint wear.

A vent that allows air pressure inside the differential housing to escape while keeping dirt and water out; a clogged breather can force lubricant past seals.

Lubricant escaping at the differential pinion shaft seal; a visible wet area or drip indicates seal wear, excessive bearing play, or a clogged breather.

A timed test with the system charged and engine off that measures pressure loss at the service brakes and parking brakes to confirm the air system is tight.

A visual or audible feature that shows when friction material has worn to its replacement limit, helping prevent rotor or drum damage and reduced braking.

A lever and linkage component that transfers air chamber force to the brake shoe or pad and adjusts automatically or manually to maintain correct pushrod stroke.

Gear oil or grease visible on the inner wheel or brake area, indicating a failed wheel seal that can contaminate brakes and lead to bearing failure.

The measured depth of grooves in a tire; minimum legal or fleet limits are checked with a gauge to ensure traction and resistance to hydroplaning.

The cold-air pressure inside a tire, checked with a calibrated gauge and set to the vehicle placard; incorrect pressure causes uneven wear, heat, and handling problems.

The amount of steering wheel movement before the front wheels begin to turn, measured to detect worn linkage, gear, or bearings that reduce control.

The difference in distance between the front and rear of the front tires; an incorrect toe setting causes rapid tire scuffing and steering pull.

A test that applies a specified current load to a battery and measures voltage to estimate its ability to crank the engine and hold charge.

A measurement of voltage loss across a circuit while current flows; excessive drop locates high resistance in cables, connectors, grounds, switches, or terminals.

A check of charging voltage and current at specified engine speed and electrical load to confirm the alternator and regulator meet the vehicle's charging needs.

An alphanumeric code stored by an electronic control module when it detects a fault, used to guide troubleshooting and verify repair completion after repair.

A filter that removes dust and debris from air returning to the passenger compartment HVAC unit; a clogged filter reduces airflow and cooling performance.

Use of electronic sensors, dyes, or pressure testing to find refrigerant escaping from HVAC components; leaks reduce cooling and can release harmful gas into the atmosphere.

A scheduled check of exit doors, windows, markings, alarms, and release mechanisms to confirm passengers can escape quickly from the bus in an emergency.

A monthly visual check of pressure gauge, seal, hose, mounting, and inspection tag to ensure the extinguisher is charged and accessible onboard.

A safety procedure that isolates energy sources and applies locks and tags before maintenance, preventing accidental startup or release of stored energy.

Clothing and gear such as safety glasses, gloves, hearing protection, and steel-toe boots worn to reduce injury during maintenance and inspection tasks.

A planned list of grease points, lubricant types, and service intervals that keeps chassis, steering, and driveline components properly lubricated and reduces premature wear.

The percentage of antifreeze in the coolant mixture, checked to ensure freeze, boil, and corrosion protection are all within the manufacturer's specification.

The distance a brake chamber pushrod travels when the brakes are applied, measured against limits to detect maladjustment or chamber problems.

Periodic moving of tires to different wheel positions to equalize wear patterns and extend tire life; direction and axle position must follow fleet guidelines.

A record completed after a pre-trip or post-trip inspection that lists defects found and certifies whether the bus is safe to operate.