Cert IV Auto Diagnostic flashcards

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

Freeze-frame data

A snapshot of sensor and operating values stored by the control module at the moment a diagnostic trouble code was set, used to reproduce the conditions of the fault.

Fuel trim

Short-term and long-term corrections the engine controller applies to injector pulse width to keep the air-fuel ratio near stoichiometric; positive values add fuel for a lean condition.

Cylinder leakage test

A test where compressed air is introduced into a cylinder at top dead centre on the compression stroke; escaping air reveals valve, ring or head gasket leakage by where it exits.

Voltage drop test

A measurement taken across a circuit while it carries current; excessive drop indicates high resistance in wiring, connectors or grounds rather than a faulty component.

Vacuum gauge diagnosis

A gauge connected to intake manifold vacuum at idle; steady 17 to 22 inches of mercury is normal, while fluctuations or low readings indicate mechanical or ignition faults.

Cam crank correlation code

A diagnostic trouble code set when the engine controller detects a mismatch between camshaft and crankshaft position signals, indicating stretched chains, jumped teeth or sensor faults.

Combustion gas test

A test that draws vapour from the cooling system through a reactive fluid; a colour change indicates combustion gases entering the coolant, confirming head gasket or head cracking.

Flexplate

The toothed disc bolted to the crankshaft on automatic vehicles that carries the starter ring gear and connects the engine to the torque converter; cracks cause engine-speed vibration.

Ohm's law

The relationship stating voltage equals current multiplied by resistance; used to predict circuit behaviour, size fuses and calculate expected readings during electrical diagnosis.

Parasitic draw

Current flowing from the battery when all circuits should be off and modules have entered sleep mode; typically should not exceed about fifty milliamps.

CAN bus termination

Two resistors of about one hundred and twenty ohms at each end of the network; measuring about sixty ohms across the bus with power off confirms both are present.

Battery load test

A test applying a high current load to a charged battery while measuring terminal voltage; cranking voltage should stay above roughly nine point six volts on a healthy battery.

Disc thickness variation

Uneven wear across a brake disc face that causes pedal pulsation as the pads grip thicker and thinner sections during each wheel rotation.

Lateral runout

Side-to-side wobble of a brake disc or hub measured with a dial indicator; excessive runout pushes the pads back and creates pulsation or a long pedal.

Caster angle

The forward or rearward tilt of the steering axis; it affects straight-line stability and self-centring, and does not cause tyre wear like camber or toe faults.

Feathered tyre wear

A wear pattern where tread blocks are worn on one edge and raised on the other, indicating incorrect toe setting or worn steering components.

Torque converter clutch slip

The difference between engine speed and input shaft speed when the converter clutch is commanded on; excessive slip causes shudder and is visible in live data.

Line pressure

Hydraulic pressure supplied by the transmission pump to apply clutches and bands; low pressure causes slipping and delayed engagement under load.

Outer CV joint wear

Wear in the constant velocity joint nearest the wheel, typically producing a rhythmic clicking noise when turning at low speed under power.

Clutch drag

Failure of the clutch to fully disengage when the pedal is pressed, causing difficult gear engagement with the engine running but normal selection with it stopped.

Refrigerant recovery

The process of removing refrigerant from a system into a recycling machine rather than venting it, required by environmental regulation before any system opening.

Non-condensable gas

Air or other gas trapped in an air conditioning system that raises high-side pressure and reduces cooling efficiency; removed by purging during recovery.

Low pressure cutout

A switch that disengages the compressor clutch when refrigerant pressure falls too low, protecting the compressor from oil starvation and preventing system damage.

Blend door actuator

A small electric motor that moves a flap inside the heater box to control air temperature; failure leaves one side or zone stuck hot or cold.

High voltage isolation

The procedure of disconnecting and verifying de-energisation of traction battery circuits above sixty volts, performed only by trained and authorised technicians.

Lockout tagout

A safety procedure where energy sources are isolated, locked and tagged so equipment cannot be re-energised while maintenance or repair work is in progress.

Asbestos dust hazard

Brake and clutch linings in older vehicles may contain asbestos; dust is controlled with wet methods and respiratory protection, never with compressed air.

Used oil containment

Storage of drained engine and transmission oil in labelled, lidded containers for licensed recycling, preventing soil and drain contamination.

Trade waste

Liquid waste generated by workshop processes, such as compressor condensate or parts washer sludge, requiring treatment or licensed disposal rather than sewer discharge.

Spill kit

A stocked set of absorbents, booms and containment equipment kept accessible so leaks of oil, coolant or solvent can be contained immediately.

Repair order authorisation

Written or recorded customer approval for quoted work and any additional repairs discovered, protecting both technician and business in later disputes.

Diagnostic record

Documentation of codes retrieved before and after repair, live data values and confirmation tests, proving the fault was correctly identified and resolved.