NAVTTC Auto Mechanic flashcards
NAVTTC Auto Mechanic · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Compression test specification
- A healthy gasoline engine typically produces 120–180 psi (8–12 bar) per cylinder, with no more than 10% variation between cylinders; lower or uneven readings indicate ring, valve, or head gasket leakage.
- Cylinder leakage test
- Regulated air is introduced into a cylinder at top dead center; leakage above 20% is excessive. Listen at the oil filler for rings, intake for intake valve, exhaust for exhaust valve, and radiator for head gasket.
- Vacuum gauge diagnosis
- A steady 17–22 inHg at idle indicates normal engine vacuum; a fluctuating needle suggests a vacuum leak or valve problem, while a low steady reading points to intake restriction or late ignition timing.
- Spark plug reading
- Tan or light brown deposits indicate normal combustion; black soot means rich mixture; white or blistered insulator means lean or overheating; oily fouling indicates worn rings or valve guides.
- Clutch free play
- Manual clutch pedal free play is typically 10–25 mm. Too much free play prevents full release and causes gear clash; too little causes slippage and release bearing wear.
- Clutch slip test
- Drive in a high gear at low speed and accelerate sharply; if engine RPM rises without a corresponding increase in vehicle speed, the clutch disc is worn and slipping.
- CV joint noise
- Clicking during turns indicates a worn outer CV joint; vibration under acceleration points to the inner joint or half-shaft. A torn boot causes grease loss and joint failure.
- Differential whine
- A whine that changes with vehicle speed suggests ring and pinion gear wear; a clunk on acceleration or deceleration indicates worn spider gears or excessive backlash.
- Brake pad minimum thickness
- Replace brake pads when friction material reaches 2–3 mm (about 1/8 inch). Brake discs must be replaced when worn below the minimum thickness stamped on the disc.
- Brake fluid service
- DOT 3 and DOT 4 glycol-based brake fluids absorb moisture and should be replaced every two years or when moisture exceeds 3%. DOT 5 silicone fluid is not compatible with DOT 3 or 4.
- Spongy brake pedal
- A spongy brake pedal indicates air in the hydraulic system and requires bleeding. A pedal that sinks to the floor suggests a fluid leak or master cylinder bypass.
- Tire wear patterns
- Inner or outer edge wear indicates incorrect camber or toe; cupping suggests worn shocks or wheel imbalance; center wear results from overinflation.
- Ohm's law
- Voltage equals current multiplied by resistance (V = I × R), and power equals voltage times current (P = V × I). For example, 12 V across 3 Ω draws 4 A and dissipates 48 W.
- Battery state of charge
- A rested 12 V battery reads 12.6 V at 100% charge, 12.4 V at 75%, 12.2 V at 50%, and below 12.0 V is discharged. Load test at half the cold cranking amp rating.
- Alternator charging voltage
- With the engine idling and accessories off, the alternator should produce 13.5–14.5 V. Below 13.0 V indicates undercharging; above 15.0 V indicates a faulty voltage regulator.
- Voltage drop test
- Measure voltage across a connection while the circuit is under load. More than 0.1 V per connection or 0.5 V total on a circuit indicates excessive resistance.
- OBD-II DTC prefixes
- Diagnostic trouble codes starting with P are powertrain, B are body, C are chassis, and U are network communication faults. Freeze frame data captures operating conditions when the fault occurred.
- Fuel pressure specification
- Port fuel injection typically runs 35–45 psi (2.5–3 bar), while direct injection runs 500–2,000 psi. Low fuel pressure causes a lean condition and misfire.
- Coolant mixture ratio
- A 50/50 mix of antifreeze and water protects to about −37°C and raises the boiling point to 129°C at 15 psi. Test concentration with a hydrometer or refractometer.
- Thermostat test
- A thermostat stuck open makes the engine run cold with poor heater output; stuck closed causes overheating. Heat it in water and verify it opens at its rated temperature, such as 82°C (180°F).
- Oil pressure warning
- If the oil pressure warning light illuminates, stop the engine immediately. Continuing to run the engine risks severe bearing and component damage from lack of lubrication.
- Total toe specification
- Total toe-in is typically 0–3 mm. Incorrect toe causes rapid tire scrub and feather-edge wear, and also affects steering wheel centering.
- Caster angle effect
- Positive caster, typically 3–8°, tilts the steering axis rearward and improves straight-line stability and steering return. Excessive caster increases steering effort.
- Thrust angle
- Thrust angle is the difference in rear toe between the left and right wheels. A non-zero thrust angle causes the steering wheel to be off-center and the vehicle to dog-track.
- Steering wheel free play
- Typical steering wheel free play is 10–30 mm at the rim. Excessive play indicates worn tie rod ends, a worn steering box, or a loose steering column.
- Tie rod and ball joint check
- With the wheel raised, play at the 9 and 3 o'clock positions indicates a worn tie rod end; play at 12 and 6 o'clock indicates a worn wheel bearing or ball joint.
- Jack stand safety
- Never work under a vehicle supported only by a jack. Place jack stands on flat, hard ground at the manufacturer's lift points before beginning any under-vehicle work.
- Torque wrench use
- Always use a calibrated torque wrench and tighten fasteners in the specified sequence, such as a spiral pattern for cylinder heads, to avoid warping and ensure even clamping.
- Multimeter connection rules
- Measure voltage in parallel with the circuit, current in series, and resistance only with the circuit de-energized. Never measure resistance on a live circuit.
- Fire extinguisher classes
- Class B extinguishers are for flammable liquid fires such as fuel and oil. Disconnect the battery before welding, and store oily rags in a closed metal container to prevent spontaneous combustion.
- Feeler gauge use
- A feeler gauge measures valve clearance, spark plug gap, and brake pad clearance. Select the blade that slides with slight drag to confirm the specified gap.
- Micrometer reading
- Read the main scale plus the thimble scale; zero-check the micrometer before use and store it with the measuring faces apart to prevent corrosion and damage.