Cert IV Auto Diagnostic key terms

An alphanumeric code stored by a control module when it detects a fault in a monitored circuit or system, used as a starting point for diagnosis.

A snapshot of sensor readings and operating conditions recorded at the moment a diagnostic trouble code is set, helping technicians reproduce the fault.

A handheld or PC-based device that communicates with vehicle control modules to read codes, view live data, and perform bidirectional tests.

Real-time sensor and actuator values displayed by a scan tool, allowing comparison of actual readings with expected values during diagnosis.

Short-term and long-term adjustments the engine control module makes to fuel delivery based on oxygen sensor feedback, expressed as a percentage.

A sensor that measures the volume or mass of air entering the engine, allowing the control module to calculate the correct fuel quantity.

A potentiometer or Hall-effect sensor that reports throttle plate angle to the engine control module for fuel and shift scheduling.

A sensor assembly on the accelerator pedal that sends driver demand signals to the control module, often with two redundant outputs for safety.

A system that uses an electric motor to open the throttle plate based on pedal input and control module commands, replacing a mechanical cable.

A sensor in the exhaust stream that generates a voltage or current signal proportional to oxygen content, used for fuel control and catalyst monitoring.

The ability of the catalytic converter to reduce harmful emissions, inferred by comparing upstream and downstream oxygen sensor signals.

A strategy that monitors crankshaft speed fluctuations to identify cylinders that fail to combust properly, setting a code and flashing the MIL if severe.

A transformer that steps up battery voltage to the high voltage needed to jump the spark plug gap and ignite the air-fuel mixture.

A device threaded into the combustion chamber that provides a gap for high-voltage spark to ignite the compressed air-fuel mixture.

A measurement of voltage lost across a conductor or connection while current flows, used to find excessive resistance in a circuit.

The relationship stating that voltage equals current multiplied by resistance (V = I × R), used to calculate expected circuit values.

Current that continues to flow from the battery when the vehicle is off, often caused by a module or accessory that fails to sleep.

A differential serial bus that allows control modules to share data over two twisted wires, reducing wiring complexity and enabling diagnostics.

A low-speed, single-wire serial bus used for simple sensors and actuators, often connected as a sub-bus to a CAN gateway.

A condition where control modules cannot exchange data due to wiring, power, ground, or internal module failure, often setting U-codes.

Adjustment of camber, caster, and toe angles so wheels are positioned correctly relative to the vehicle and road for even tire wear and straight tracking.

Characteristic wear shapes such as cupping, feathered edges, or center wear that indicate alignment, inflation, or suspension problems.

A vehicle tendency to drift to one side while driving straight, caused by alignment, tire, brake, or steering component issues.

The presence of moisture, air, or wrong fluid in the hydraulic brake system, which can reduce braking performance and damage seals.

The sensation transmitted to the driver through the brake pedal, such as sponginess, pulsation, or firmness, indicating hydraulic or component condition.

A system that modulates brake pressure during hard braking to prevent wheel lockup and maintain steering control.

A sensor that measures the rotational speed of a wheel, providing input to ABS, traction control, and stability systems.

A test that measures hydraulic pressure in transmission fluid circuits at specified engine speeds and gear ranges to assess pump and circuit condition.

The color, smell, and presence of debris in automatic transmission fluid, used as an indicator of internal wear or overheating.

An electrically controlled valve that directs hydraulic pressure to engage or release transmission clutches and bands for gear changes.

The process of confirming which refrigerant is in an air conditioning system using a tester, preventing cross-contamination and unsafe recovery.

The safe removal and storage of refrigerant from an air conditioning system before repair, required by environmental regulations.

The use of electronic sniffers, UV dye, or pressure testing to locate refrigerant leaks in air conditioning components and lines.

Safety gear such as gloves, eye protection, and respirators worn to protect the technician from hazards in the workshop.

The correct handling and disposal of substances like used oil, coolant, and refrigerant according to environmental regulations.

A document that provides information about the hazards, safe handling, and emergency measures for a chemical product.

A document that records the customer's complaint, authorized work, parts used, and technician notes for a repair job.

The step of confirming the customer's reported concern by test driving or inspecting the vehicle before beginning diagnosis.

A documentation format that states the customer's concern, the root cause found, and the correction performed, ensuring clear communication and records.