Automotive Servicing NC III flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Personal protective equipment

Safety gear worn during automotive work: eye protection, oil-resistant gloves, steel-toe boots, hearing protection above 85 dB(A), and a respirator when spraying paint or handling brake dust.

Lockout/tagout

Procedure that isolates a machine's energy source, applies a personal lock and tag, and verifies zero energy before service. Applies to lifts, compressors, and tire machines.

Refrigerant recovery requirement

R-12 and R-134a must be recovered with certified equipment and never vented to atmosphere. Recovery protects stratospheric ozone and reduces greenhouse gas release.

Torque wrench calibration

Click-type wrenches are checked at least annually or after a drop and stored at the lowest scale setting. Beam-type wrenches need no adjustment but must be read at eye level.

Six-point versus twelve-point socket

Six-point sockets contact fastener flats and resist rounding. Twelve-point sockets allow indexing in tight spaces but grip the corners and are more likely to round a worn fastener.

Micrometer least count

Smallest reading the instrument resolves. A metric micrometer with 0.5 mm sleeve graduations and a 50-division thimble resolves 0.01 mm per thimble division.

Vernier caliper least count

Smallest main scale division divided by the number of vernier divisions. A common metric caliper with 1 mm main divisions and 50 vernier divisions reads to 0.02 mm.

Impact socket use

Impact-rated black sockets are used only with impact wrenches. Chrome sockets can crack or shatter under impact loading and should never be used on powered impact tools.

Engine displacement formula

Displacement per cylinder equals (pi divided by 4) times bore squared times stroke. Multiply by the number of cylinders for total displacement, keeping bore and stroke in one unit.

Compression ratio formula

Compression ratio equals swept volume plus clearance volume, divided by clearance volume. Swept volume is one cylinder's displacement; clearance volume is chamber volume at top dead center.

Ohm's law and power

Voltage equals current times resistance. Power equals voltage times current, also current squared times resistance or voltage squared divided by resistance. Used to size fuses and find resistance.

Gear ratio calculation

Driven gear teeth divided by drive gear teeth. Overall ratio is the product of each stage; final drive ratio is ring gear teeth divided by pinion gear teeth.

Voltage drop limit

A healthy circuit drops less than 0.1 V per connection and less than 0.5 V total on the ground side under load. Higher readings identify excessive resistance.

First-angle versus third-angle

First-angle projection places each view on the side opposite the observer; third-angle places it on the observer's side. ISO drawings commonly use first-angle, North American drawings third-angle.

Hidden line convention

Dashed lines represent edges not visible in the current view. Solid thick lines show visible outlines, and chain lines mark centerlines and cutting planes.

Service limit versus new value

Specification tables list both new dimensions and the wear limit for replacement. A part is replaced when it exceeds the service limit, not merely when it differs from new.

Fastener grade markings

Metric classes 8.8, 10.9, and 12.9 and SAE grades 5 and 8 mark increasing tensile strength. Replacement fasteners must match the original grade and thread type.

OBD-II code structure

First character gives the system: P powertrain, B body, C chassis, U network. The second digit identifies the sub-system, such as misfire codes in the P0300 series.

Fuel trim interpretation

Positive long-term trim means the ECU is adding fuel for a lean condition such as a vacuum leak. Negative trim means removing fuel for a rich condition such as a leaking injector.

Compression test rule

Crank with the throttle open and all plugs removed. A cylinder more than 10 to 15 percent below the highest reading, or one that improves on a wet test, indicates ring wear.

Cylinder leakage test

Regulated air is applied at top dead center. Leakage heard at the intake, exhaust, oil filler, or radiator identifies the intake valve, exhaust valve, rings, or head gasket.

Parasitic draw threshold

Current drain measured after modules sleep. A drain above roughly 50 mA is abnormal and is isolated by pulling fuses while watching the clamp meter reading.

Torque-to-yield bolts

Head bolts that stretch permanently when tightened and must be replaced each time. Follow the manual's staged sequence, usually starting at the center and working outward.

Timing mark verification

Align all timing marks before belt or chain removal. After installation, rotate the engine two full turns by hand and recheck alignment before starting an interference engine.

Piston ring end gap

Measured with the ring squared in the bore, pushed down by a piston. File-fit rings are filed to the specified gap and never below the minimum value.

Cylinder bore measurement

Measure at top, middle, and bottom in two perpendicular directions. Taper and out-of-round beyond the service limit require boring or cylinder replacement.

Brake fluid hygroscopicity

DOT 3 and DOT 4 glycol fluids absorb moisture, lowering boiling point and promoting corrosion. DOT 5 is silicone-based and must never be mixed with glycol fluid.

Wheel alignment angles

Camber is wheel tilt, caster is steering axis tilt, and toe is the front-to-rear difference. Toe causes the most tire wear and is set last after camber and caster.

ABS wheel speed sensor fault

A faulty sensor or tone ring sets an ABS code and disables anti-lock function. Check air gap, tone ring condition, and wiring continuity before replacing the control module.

Clutch slip symptom

Engine rpm rises without matching vehicle speed, especially under load or on hills. Causes include worn disc friction material, weak pressure plate, or oil contamination.

Differential backlash

Rotational play between ring gear and pinion, measured with a dial indicator. Incorrect backlash causes whine and accelerated gear wear; pinion preload is set with shims or a crush sleeve.

Three Cs of repair order

Complaint in the customer's words, cause verified by diagnosis, and correction actually performed. Complete entries support warranty claims and protect both shop and customer.