ASE G1 cheat sheet

Four-stroke cycle order is intake, compression, power, exhaust; the crankshaft rotates two full turns per complete cycle.

Stoichiometric gasoline air-fuel ratio is about 14.7:1 by mass under ideal combustion conditions.

A coolant thermostat begins opening near its rated temperature, commonly 180 to 195 degrees Fahrenheit, and reaches full opening above that rating.

Valve clearance is measured with a feeler gauge between the cam base circle and follower or valve stem, then compared with specification.

A stuck-closed PCV valve can allow crankcase pressure to build and force oil past seals.

An interference-engine timing belt failure can cause piston-to-valve contact and severe cylinder head damage.

An oil pressure warning switch typically closes to ground when pressure falls below a low threshold, commonly about 5 to 7 psi.

A cooling system pressure cap raises the boiling point by roughly 3 degrees Fahrenheit per psi of rating.

Cylinder leak-down air escaping from the intake indicates an intake valve leak; escaping from the oil filler indicates ring or cylinder wear.

Automatic transmission fluid level is usually checked with the engine running and fluid warm, in Park or Neutral, or at an overflow plug at a specified temperature.

The torque converter stator multiplies torque at low speed ratio and approaches a fluid coupling near 1:1 speed ratio.

A failed shift solenoid can cause harsh shifting, a missing shift, or default limp mode operation.

Burnt fluid smell and debris indicate overheating or clutch material wear; color alone is not a definitive diagnosis.

Transmission line pressure typically increases with throttle opening and engine load.

A CVT changes ratio continuously with a steel belt or chain and variable-diameter pulleys and requires the specified CVT fluid.

After valve body or clutch repair, the transmission control module may require an adaptive relearn to restore shift quality.

A faulty vehicle speed sensor can cause incorrect shift points, no upshift, and speedometer error.

Torque converter clutch shudder is often caused by degraded automatic transmission fluid or a worn converter clutch lining.

Clutch pedal free play is the clearance before the release bearing contacts the pressure plate; too little clearance can cause slip and bearing wear.

Manual transmission gear oil is checked at the fill plug with the vehicle level; fluid should be at the bottom edge of the fill hole.

A rhythmic click during turns usually indicates a worn outer CV joint; vibration under acceleration often indicates an inner CV joint.

Differential ring and pinion backlash is measured with a dial indicator against a tooth while the pinion is held stationary.

Clutch-type limited-slip differentials often require a friction modifier to prevent chatter during low-speed turns.

A worn universal joint can cause driveline vibration, a clunk during load changes, or a squeak during rotation.

Flywheel runout and step height affect clutch engagement and must be measured against specification during clutch service.

A leaking axle seal can contaminate brake shoes or pads and cause brake pull, noise, or lockup.

Toe is the difference in track width measured at the front and rear of the tires; toe-in means the fronts are closer together than the rears.

Camber is the inward or outward tilt of the tire top relative to vertical; negative camber tilts the top inward.

Positive caster tilts the steering axis rearward at the top and improves straight-line stability and steering return.

Ride height should be checked before alignment because bent or sagging suspension components cannot be adjusted out.

Tire pressure affects rolling resistance, wear pattern, and TPMS operation; pressure should be set cold.

A worn tie rod end produces steering play and can cause uneven toe wear.

A MacPherson strut combines the spring and damper; a worn strut mount bearing can cause popping when turning.

Power steering whine is often caused by low fluid or air in the system and may require bleeding after repair.

Wheel bearing noise often changes when vehicle weight shifts side to side, helping identify the affected side.

Glycol-based brake fluid is hygroscopic; absorbed moisture lowers its boiling point and can cause pedal fade under heavy braking.

DOT 3, DOT 4, and DOT 5.1 fluids are glycol-based; DOT 5 is silicone-based and must not be mixed with glycol fluid.

A disc brake rotor has a minimum thickness specification stamped or cast on the hub; a rotor below specification must be replaced.

Brake pedal pulsation is commonly caused by rotor thickness variation or lateral runout.

Brake drag can overheat the brakes, cause a pull, and accelerate pad wear; caliper slides and flexible hoses are common causes.

An illuminated ABS warning lamp indicates the antilock function is disabled, but conventional hydraulic brakes normally remain functional.

A parking brake should hold the vehicle and release without drag; adjustment is set to the specified lever travel or click count.

Brake line flares must match the fitting type, such as ISO bubble or double flare, to prevent leaks.

Contaminated brake pads or shoes from oil or grease can cause pulling, noise, and reduced friction.

Ohm's law states V equals I times R; power can be calculated as P equals V times I, I squared times R, or V squared divided by R.

A voltage drop test measures loss across a circuit under load; excessive drop indicates high resistance in cables, connections, switches, or grounds.

Parasitic draw is measured with an ammeter in series after modules sleep; excessive draw is commonly specified below about 50 milliamps.

A fully charged lead-acid battery at rest typically measures about 12.6 volts open-circuit; lower voltage indicates partial discharge.

Series circuits share the same current; parallel circuits share the same voltage.

A relay coil can be controlled on the power side or ground side, so both control circuits must be verified.

A healthy CAN bus typically measures about 60 ohms across the communication lines because two 120-ohm terminating resistors are in parallel.

Charging voltage with the engine running is typically about 13.5 to 14.5 volts, depending on temperature and battery state.

A fuse must be replaced with the same rating because the fuse protects the wiring from overload.

Refrigerant must be recovered with approved equipment and not vented to the atmosphere.

With the compressor engaged, low-side A/C pressure commonly reads about 25 to 45 psi, varying with ambient temperature and system design.

High-side A/C pressure commonly reads about 150 to 250 psi, depending on ambient temperature, condenser airflow, and refrigerant charge.

A compressor clutch that does not engage can be caused by low refrigerant pressure, an open pressure switch, a fuse, a relay, or incorrect clutch gap.

The blend door actuator moves a flap that directs air through or around the heater core to control outlet temperature.

A restricted cabin air filter reduces airflow and can cause weak vent output or persistent odors.

No cabin heat can result from low coolant, a stuck-open thermostat, a failed blend door, or a blocked heater core.

Refrigerant leaks are located with UV dye, an electronic leak detector, or soap bubbles, not by opening the system.

A good vacuum reading during A/C evacuation is about 28 to 30 inches of mercury, indicating moisture and air removal.

Positive fuel trim means the control module is adding fuel to correct a lean condition; negative fuel trim means it is reducing fuel.

Diagnostic trouble code P0171 indicates bank 1 is lean; P0172 indicates bank 1 is rich.

A properly switching upstream oxygen sensor oscillates between about 0.1 and 0.9 volt.

The misfire monitor detects crankshaft speed fluctuations that occur when a cylinder fails to produce power.

A MAP sensor measures manifold pressure; with the key on and engine off, it should read near atmospheric pressure.

Ignition timing typically advances with engine speed and light load and retards when knock is detected.

A compression test is performed with the throttle open and all spark plugs removed; cylinder results should be within about 10 to 15 percent of each other.

An evaporative emission large-leak code such as P0455 is commonly caused by a loose fuel cap, disconnected hose, or failed purge valve.

A mass airflow sensor reading can be compared with specification at idle and at higher engine speed to identify contamination or airflow faults.