Automotive Servicing NC III cheat sheet

Personal protective equipment for automotive work: safety glasses with side shields, oil-resistant nitrile gloves, steel-toe boots, hearing protection above 85 dB(A), and a respirator (NIOSH-approved) when spraying paint or handling brake dust.

Before working under a raised vehicle, confirm the lift's rated capacity exceeds the vehicle weight, engage the mechanical safety lock, and place jack stands under the manufacturer-specified lift points; a hydraulic jack alone is never a support device.

Store flammable liquids (gasoline, solvent, paint thinner) in approved self-closing safety containers, away from ignition sources; the flash point of gasoline is about -43 degrees C, so vapor ignition is possible at ambient temperature.

Battery charging releases hydrogen gas; keep flames and sparks away, ventilate the area, and disconnect the negative terminal first and reconnect it last to avoid short circuits.

Brake dust from older linings may contain asbestos; never blow it with compressed air. Use a wet method or a HEPA vacuum, and treat any unknown lining as asbestos-containing.

Waste segregation rules: used oil, oil filters, coolant, brake fluid, lead-acid batteries, tires, and solvent rags are separate waste streams. Coolant (ethylene glycol) is toxic and must never be poured into drains or soil.

Refrigerant handling: R-12 and R-134a deplete ozone or contribute to global warming and must be recovered with certified recovery equipment; venting refrigerant to atmosphere is prohibited.

Fire classes and extinguishers: Class A (ordinary combustibles), B (flammable liquids), C (energized electrical), D (combustible metals). Use ABC dry chemical in general shop areas and CO2 near electrical panels.

Lockout/tagout applies to shop equipment: isolate the energy source, apply a personal lock and tag, and verify zero energy before servicing a lift, compressor, or tire machine.

Torque wrench types: click-type (audible/tactile release at set torque), beam-type (deflection scale, no adjustment needed), and electronic. Calibrate click-type wrenches at least annually or after a drop; store them at the lowest scale setting.

Torque conversion: 1 N·m = 0.7376 lb-ft; 1 lb-ft = 1.356 N·m; 1 lb-in = 0.113 N·m. Always verify the unit marked on the wrench against the specification unit.

Six-point sockets contact the fastener flats and resist rounding; twelve-point sockets allow indexing on tight angles but grip corners. Use impact-rated (black) sockets only with impact tools.

Micrometer reading: main scale value plus thimble reading multiplied by the least count. A metric micrometer with 0.5 mm sleeve graduations and a 50-division thimble has a least count of 0.01 mm.

Vernier caliper least count = smallest main scale division divided by number of vernier divisions; a common metric caliper reads 0.02 mm.

Dial indicator and magnetic base: measure runout, end play, and backlash. Zero the indicator against a known surface and confirm the plunger travel is within range before reading.

Hydraulic press and puller use: support the workpiece squarely, never stand in line with the ram, and use the correct adapter so force is axial; off-axis loading can shatter cast parts.

Compressed air safety: shop air is typically regulated to 90-120 psi; never use it to clean skin or clothing, and use a nozzle rated at 30 psi or less for cleaning parts.

Tool inspection rule: remove from service any tool with cracks, mushroomed heads (chisels, punches), frayed cords, missing guards, or damaged insulation on double-insulated power tools.

Engine displacement for one cylinder = (pi / 4) x bore^2 x stroke. Total displacement = that value x number of cylinders. Keep bore and stroke in the same unit before converting.

Compression ratio = (swept volume + clearance volume) / clearance volume. Swept volume equals cylinder displacement; clearance volume is the combustion chamber volume at TDC.

Unit conversions: 1 inch = 25.4 mm; 1 mm = 0.03937 in; 1 liter = 1000 cm^3; 1 cubic inch = 16.387 cm^3; 1 kg = 2.2046 lb; 1 psi = 6.895 kPa.

Piston speed (mean) = 2 x stroke x rpm. Example: 90 mm stroke at 3000 rpm gives 2 x 0.090 m x 3000 = 540 m/min, or 9 m/s.

Ohm's law: V = I x R. Power: P = V x I = I^2 x R = V^2 / R. Use these to size fuses and diagnose excessive circuit resistance.

Voltage drop test: a good circuit should drop less than 0.1 V per connection and less than 0.5 V total on the ground side under load. Higher readings indicate resistance.

Gear ratio = driven gear teeth / drive gear teeth. Overall ratio = product of each stage; final drive ratio = ring gear teeth / pinion teeth.

Percentage and tolerance: allowable range = nominal plus or minus (nominal x tolerance percent). A 50.00 mm shaft with plus or minus 0.02 mm tolerance is acceptable from 49.98 to 50.02 mm.

Hydraulic pressure = force / area (P = F / A). A 500 N force on a 10 cm^2 piston produces 50 N/cm^2, or about 500 kPa.

First-angle projection (common in ISO/European drawings): the view is placed on the side opposite the observer. Third-angle projection (common in North America): the view is placed on the same side as the observer.

Line conventions: solid thick lines are visible outlines; dashed lines are hidden features; chain or phantom lines mark centerlines and cutting planes; thin lines are dimension and extension lines.

Dimension tolerances: bilateral (plus/minus both sides), unilateral (one side only), and limit dimensions (maximum and minimum stated directly). Always read the tolerance block before machining.

Surface finish symbol Ra gives the arithmetic average roughness in micrometers; lower Ra means a smoother finish. Note the machining allowance before boring or honing.

Torque specification reading: distinguish dry vs lubricated threads, and note whether the value is for a bolt into aluminum or steel. Reused torque-to-yield bolts must be replaced, not re-torqued.

Service manual structure: general information, maintenance, engine, drivetrain, chassis, body, and wiring diagrams. The VIN and engine/transmission codes select the correct section.

Wiring diagram symbols: the ground symbol is a horizontal bar set; a switch is shown in its de-energized position; wire color codes appear as letters (for example, B/Y means black with a yellow stripe).

Clearance and specification tables give new and service-limit values. A part is replaced when wear exceeds the service limit, not when it merely differs from the new value.

Fastener grade markings: metric class 8.8, 10.9, and 12.9 and SAE grade 5 and 8 indicate increasing tensile strength. Match replacement fasteners to the original grade.

Diagnostic sequence: verify the complaint, gather symptoms, check for stored DTCs, perform a visual and basic inspection, then test by symptom. Do not replace parts based on a code alone.

OBD-II code structure: P (powertrain), B (body), C (chassis), U (network). The second digit identifies the sub-system; for example, P0300-series codes indicate misfire.

Three essentials for combustion: correct air-fuel ratio (about 14.7:1 stoichiometric for gasoline), sufficient compression, and adequate spark at the right time. Isolate which one is missing.

Fuel trim interpretation: positive long-term fuel trim (adding fuel) suggests a lean condition such as a vacuum leak; negative trim (removing fuel) suggests a rich condition such as a leaking injector.

Scan tool live data: compare coolant temperature sensor, intake air temperature, MAF, MAP, and O2 sensor readings against expected values; a lazy O2 sensor switching slowly indicates a worn sensor.

Voltage drop and parasitic draw: measure current drain with a clamp meter after modules sleep; a drain above about 50 mA (0.05 A) is abnormal and must be isolated by fuse pulling.

Compression test: crank with the throttle open and all spark plugs removed; a cylinder more than 10-15 percent below the highest reading, or a wet test that raises compression, points to ring wear.

Cylinder leakage test: apply regulated air at TDC and listen for leakage at the intake (intake valve), exhaust (exhaust valve), oil filler (rings), or radiator (head gasket).

Diesel diagnostics: hard starting with white smoke suggests low compression or glow plug failure; black smoke suggests over-fueling or restricted intake; blue smoke suggests oil consumption.

Torque-to-yield (TTY) head bolts stretch during tightening and must be replaced each time; follow the manual's sequence, usually from the center outward in stages.

Valve clearance adjustment: measure with a feeler gauge when the engine is cold (or hot, per specification), then set intake and exhaust to the specified range. Too tight causes burned valves; too loose causes noise and reduced lift.

Timing belt and chain service: align all timing marks before removal, rotate the engine two full turns by hand after installation, and recheck alignment before starting. Interference engines suffer valve damage on misalignment.

Piston ring end gap is measured with the ring squared in the bore using a piston to push it down; file-fit rings are gapped to the specification, never filed below the minimum.

Cylinder bore measurement: measure at the top, middle, and bottom in two perpendicular directions (thrust and axial). Taper and out-of-round beyond the service limit require boring or replacement.

Bearing clearance check: use Plastigauge or a micrometer with bore gauge. Oil clearance is typically 0.02-0.06 mm for many main and rod bearings; verify against the manual.

Diesel-specific service: injector hold-down torque and seat cleaning matter; air in the fuel system after filter change requires priming. Never crack high-pressure lines on common-rail systems while the engine is running.

Cooling system service: pressure test the system to the cap rating, check the thermostat opening temperature, and bleed air per the manual. A failed head gasket can show bubbles in the radiator or hydrocarbon in coolant.

Lubrication: match oil viscosity and API/ACEA service category to the specification. Low oil pressure at idle with a worn pump or excessive bearing clearance shows as a gauge drop and valve train noise.

Brake hydraulic principle: pedal force multiplied by pedal ratio and hydraulic advantage (P = F/A). Air in the system is compressible and causes a spongy pedal; bleed in the manufacturer's sequence.

Brake fluid: DOT 3 and DOT 4 are glycol-based and hygroscopic, absorbing moisture that lowers the boiling point; DOT 5 is silicone-based and must not be mixed with glycol fluids.

Disc brake service: measure rotor thickness against the minimum, check runout with a dial indicator, and lubricate slide pins with high-temperature silicone grease, not ordinary chassis grease.

Drum brake adjustment and self-adjuster direction matter; incorrect installation causes drag or no adjustment. Check wheel cylinder leakage and replace hardware in axle sets.

Wheel alignment angles: camber (inward/outward tilt), caster (steering axis tilt), and toe (front-to-rear difference). Toe is the largest tire-wear factor; set toe last after camber and caster.

Suspension inspection: check ball joints for vertical and horizontal play with the wheel unloaded, check tie-rod ends for play, and inspect struts for leakage and torn boots.

Tire and wheel service: torque wheel nuts in a star pattern to specification, check runout and balance, and match tire load index and speed rating. Under-torque loosens; over-torque stretches studs.

ABS diagnostics: a wheel speed sensor fault sets an ABS code and disables ABS. Check sensor air gap, tone ring condition, and wiring continuity before replacing the module.

Steering system: power steering fluid type matters (ATF vs dedicated fluid). A whine with aeration indicates air ingress or a failing pump; check belt tension and reservoir level first.

Manual transmission: check gear oil level at the fill plug (fill until it runs out), use the specified viscosity and GL rating, and inspect synchro wear by grinding on downshift.

Clutch service: measure clutch disc thickness and flywheel runout; replace the release bearing and pilot bearing with the clutch. A slipping clutch shows as engine rpm rising without vehicle speed.

Automatic transmission: fluid level is checked with the engine running at operating temperature in the specified range (often Park or Neutral per the manual). Use only the specified fluid type.

Torque converter and stall: a stall test at wide-open throttle in Drive and Reverse compares engine rpm; a low stall in all ranges suggests a converter or engine power problem, high stall suggests slipping clutches.

CV joint and driveshaft: torn boots allow grease loss and dirt ingress; a clicking noise on turns points to an outer CV joint, and vibration at speed points to a worn inner joint or imbalance.

Differential service: check backlash with a dial indicator, set pinion preload with a crush sleeve or shims, and use the specified gear oil plus limited-slip additive where required.

4WD and transfer case: check for mismatched tire diameters, which cause driveline wind-up; engage ranges only as specified (stopped or rolling), and verify actuator and switch operation.

Gear ratio calculation: overall drive ratio = transmission gear ratio x final drive ratio. A numerically higher ratio increases torque at the wheels and reduces top speed.

Driveline vibration diagnosis: note whether vibration changes with speed, engine rpm, or turning. U-joint phasing and driveline angle errors cause speed-related vibration.

Work order content: customer information, VIN, odometer, complaint in the customer's words, diagnosis, parts used, labor performed, and technician signature. It is the legal and warranty record.

Three Cs of a repair order: complaint (what the customer reports), cause (the verified root cause), and correction (the action taken). Vague entries such as 'fixed' fail audit and warranty review.

Parts documentation: record part number, quantity, and whether the part is new, remanufactured, or used. Retain removed parts for customer inspection or warranty return as required.

Quality control checks: verify torque values, fluid levels and types, fastener presence, tool and rag count, and a road test before release. A second-person inspection is used for safety-critical work.

Torque and specification traceability: keep the manual or specification sheet with the job record so the repair can be audited against the manufacturer's values.

Warranty and comeback handling: log the return reason, re-diagnose rather than repeat the previous repair, and document the root cause to prevent recurrence.

Customer communication: explain the fault in plain language, present the estimate with parts and labor separated, obtain approval before additional work, and state the warranty terms.

Shop recordkeeping: maintain calibration records for torque wrenches and diagnostic equipment, refrigerant recovery logs, and waste disposal manifests as required by regulation.

Final inspection checklist: lights, horn, wipers, fluid leaks, tire pressures, and warning lamps. Confirm that no diagnostic trouble codes remain and that monitors are ready if an emissions test follows.