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Automotive Definitions

The following are key words and phrases used in articles that have run in Tomorrow’s Technician magazine. This helpful reference guide can be printed out and added to your class notes. We will continue to update this list.

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  Key Automotive Definitions:

Acceleration Simulation Mode (ASM): A system of testing vehicle exhaust emissions that simulates a constant vehicle acceleration load.

Acceleration Simulation Mode (ASM) Test: A method of emissions testing that utilizes a dynamometer to simulate constant acceleration.

Accumulator: A tank incorporated into a vehicle’s air conditioning system that contains a desiccant to absorb moisture from the refrigerant. 

Antilock brake systems — An advanced system designed to prevent the brakes from locking up and skidding when braking hard or when braking on wet or slick surfaces through the use of electrically operated solenoid valves that hold, release and reapply hydraulic pressure to the brakes.

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ABS warning light  — An indicator light on the instrument panel that warns the driver when there is a problem with the ABS system. If the light fails to go out or comes on while driving, it signals a potential problem with the ABS system. The light is also used for diagnostic purposes when retrieving flash codes (trouble codes) from the ABS module.

Air Injection Reactor (AIR): The emissions control system that pumps air into the exhaust system to burn off hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) in the exhaust.

Air Pump: A component of the air injection reactor (AIR) system that pumps air to mix in the exhaust gases and to continue the burning of HC and CO in the exhaust. 

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Alphanumeric: A combination of letters and numbers.

Alternating Current (AC): An electrical current that flows alternately in two directions, forward and backward. It may be created by an alternator or, as is common in household electrical systems, by an electrical generating plant. 

Ambient: Surrounding, or all around (e.g., ambient temperature).

Atmospheric pressure: The pressure caused by the weight of the Earth’s atmosphere. At sea level, atmospheric pressure is 14.7 psi (101 kPa). 

Bidirectional Control: A part of the OBD II program that enables a scan tool to send a command to a computer actuator. 

Blend Door: A part of a vehicle’s air conditioning system that controls the ratio of incoming heated air and fresh air. This ratio is adjusted to control the temperature in the passenger compartment.

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Blowby: The unburned fuel and combustion byproducts that leak past the piston rings and into the crankcase. 

Borescope: A device used to look inside areas of an engine or other components that would otherwise require disassembly to view.

Capacitor: A device that can store voltage without affecting it. It’s made up of two conductive surfaces positioned close together, separated only by an insulator. Also often called a condenser

Carbon Dioxide (CO2): An odorless, colorless and harmless incombustible gas formed when carbon monoxide from the exhaust is mixed with air (oxygen).

Controller Area Network (CAN) — The basic integrated operating system for the wiring and electronics in late model vehicles. The CAN system ties together all the major control modules in the vehicle and allows them to “talk” to each other and share data. CAN’s integrated network allows the powertrain control module, body control module, antilock brake module, airbag module, climate control module, lighting control modules, electronic instrument cluster, keyless entry system, tire pressure monitoring system and all the other modules to work together.

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Data Communications BUS — The communications network in a vehicle that allows multiple control modules to communicate with each other. The speed or baud rate at which information flows over the bus network is determined by various design protocols.

Data Link Connector — The diagnostic communications connector on a vehicle that enables a scan tool to communicate with the Powertrain Control Module (PCM) and/or other onboard modules. On 1996 and newer OBD II vehicles, the connector is usually located under the dash near the steering column.

Diagnostic Trouble Code (DTC)  — A troubleshooting code that is set in a vehicle’s onboard computer when a fault occurs in any monitored system. The code number corresponds to the type of fault and is used to diagnose the problem. 

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Digital volt-ohm meter (DVOM) or digital multimeter (DMM) — A piece of equipment that typically combines the functions of a voltmeter, ohmmeter and ammeter into one. It can display voltage readings, resistance (ohms) readings, and amperage (current) readings. Some of the better units can also display frequency and dwell, as well as pressure and temperature with the appropriate probes.

Electronic Brake Control Module (EBCM) or Electronic Brake Module EBM) — A microprocessor in the ABS system that functions like the engine control computer and uses input from its sensors to regulate hydraulic pressure during braking to prevent wheel lockup.

Emissions (gas) analyzer — A piece of diagnostic equipment used to reveal the exact composition of the exhaust gases that are coming out of the engine. Emission analyzers are available in a variety of configurations, including 4-gas and 5-gas units, and portable and stationary units. Four-gas units read hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) and oxygen (O2). Five-gas units read all of these plus nitric oxides (NOx). These analyzers help the technician “see” if the fuel mixture is running rich or lean, and if a misfire is ignition, compression or fuel related. 

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Emission control system — The vehicle components that are responsible for reducing air pollution. The emission control system, an integral part of the engine that should not be tampered with or disconnected, regulates crankcase emissions, evaporative emissions and tailpipe exhaust emissions.

Electronically Erasable Program Read Only Memory (EEPROM) — A description of a chip or module that can store operating instructions, as well as accept a corrected electronic code, allowing new information to overwrite the old information (flash reprogramming). 

Engine control module (ECM) — The computer or electronic control module that regulates engine functions such as spark timing, fuel delivery and other emissions functions. If the unit also it incorporates transmission control functions, it is then referred to as a Powertrain Control Module (PCM).

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Engine Control Module (ECM) — A programmed electronic component that regulates various aspects of a vehicle’s engine, including timing and fuel distribution. The unit consists of a computerized circuit board mounted on the engine. 

EVAP System — The Evaporative Emission Control System (EVAP), an important integral part of the vehicle’s emission control system, prevents the escape of fuel vapors from the fuel system and fuel tank. Fuel vapors are vented to a charcoal-filled storage canister, and are then vented into the engine through a purge valve to be reburned when the engine is running.

Evaporative emissions — Fuel vapors that are released into the atmosphere from a vehicle’s fuel system, normally from a damaged fuel cap. 

Exhaust Gas Recirculation (EGR) — An emissions control technique for reducing oxides of nitrogen emissions in the tailpipe where a small amount of exhaust gas is recirculated back into the intake manifold to dilute the incoming air/fuel mixture.

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EGR valve — The main control device in the Exhaust Gas Recirculation system. 

Flash Codes — Fault codes or diagnostic trouble codes that are read by counting flashes of the Check Engine light or ABS warning light. While not available on all vehicles, flash codes offer essential diagnostic information for troubleshooting problems.

Freeze Frame Data — Data such as sensor values, engine rpm, coolant temperature, vehicle speed, and others are captured or stored by a scan tool or by the OBD II system when a fault occurs. Useful in diagnosing intermittent faults. 

I/M 240 — Inspection/Maintenance or an "enhanced" emissions testing program with a tailpipe test that lasts 240 seconds using a dynamometer to simulate actual driving conditions.

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J2534 pass-through tool — A piece of equipment unit that allows communication between a PC (or other data-storing device) and the vehicle’s powertrain control module (PCM) for the purpose of reprogramming (flashing) modules. J2534 is the communication standard created for universal flash programming. 

Malfunction Indicator Lamp (MIL) or Check Engine Lamp — a dashboard warning light used on 1996 and newer vehicles equipped with OBD II systems that comes on if the computerized engine control system detects an engine performance or emissions problem.

Mode $06 — An advanced diagnostic mode within OBD II that identifies how all of the sensors and other emission control components are functioning. Mode $06 is accessed with a professional grade scan tool and software that can convert the hexadecimal (16-bit computer code) into ordinary numbers and values 

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Onboard Diagnostics II (OBD II) — The second-generation emissions diagnostic system required on all 1996 and newer vehicles that monitors vehicle emissions, and illuminates the Check Engine (CE) or Malfunction Indicator Lamp (MIL) if it detects a problem that causes emissions to exceed the federal limits by 50% or more.

Onboard diagnostics — Software in the engine control module or powertrain control module that runs self-diagnostic checks on the control module, sensors and other related emissions systems. When a fault is found, the software sets a diagnostic trouble code and turns on the CE/ MIL lamp. 

Refrigerant identifier — A piece of A/C equipment used by repair shops to identify and verify the type of refrigerant in a vehicle’s A/C system before servicing. Identifiers reduce the risk of cross-contaminating the A/C recovery/recycling equipment.

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Refrigerant recovery machine — A piece of A/C equipment used when servicing a vehicle’s A/C system to prevent refrigerant from escaping into the atmosphere (venting) in accordance to federal law. 

Scan Tool — An electronic diagnostic tool that plugs into a vehicle’s diagnostic connector to read fault codes, sensor data and other system information. Scan tools use software that must be compatible with the vehicle application. Access to certain data or display information is dependent on the tool.

Transmission Control Module (TCM) — An electronic control module or computer that regulates the operation of the transmission. This unit can be integrated into the Powertrain Control Module, eliminating the need for a separate TCM control module. 

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Vehicle identification number (VIN)  — A unique 17-character identification marker made up of numbers and letters used on every car and light truck since model year 1981 and is used to unlock important information about a vehicle’s history — including identifying the engine, transmission and brake systems. The VIN, located on the dashboard and driver’s side door jamb, also is useful in assisting in the replacement of parts, identifying vehicles in OE recalls, as well as used by law enforcement agencies to identify and recover stolen cars and car parts. Auto manufacturers use VINs when they resolve safety recalls.

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