Terminology and Abbreviations

A/F – Air/Fuel Ratio.

AIR – Air Injector Reaction System – Fresh air is pumped into the exhaust system to reduce emissions.

ALCL – Assembly Line Communication Link – Used during vehicle assembly to evaluate computer command control and for service to flash check engine light to see if there are any trouble codes and use as a data connection to the ECM.

ALDL – Assembly Line Data Link – (same as ALCL).

A.C. – Alternating Current – And electric current that has its polarity constantly changing from positive to negative and back again.

A/C – Air Conditioning.

AMPERAGE – The total amount of current (amperes) flowing in a circuit.

AMP – Ampere – The unit of measurement for the flow of electronics in a circuit.

ANALOG SIGNAL – A signal which varies in exact proportion to a measured quantity; such as pressure, temperature, speed, etc.

B+  Battery Positive Voltage (12v).

BARO – Barometric Absolute Pressure Sensor – Reads atmospheric pressure.

BAT – Positive Battery Terminal.

BATTERY – A group of two or more cells connected together for the production of an electric current by converting chemical energy into electrical energy.

BIAS – The term applied to the electrical, mechanical, or magnetic force or voltage applied to a device to establish the reference point for operation.

BINARY – A numbering system using a base number or radix of 2.  In the binary system, the only two digits are 1 and 0.

BINARY COUNTER – A counter which produced an output pulse for each two input pulses.

BIT – The smallest unit of information recognized by a computer.

BUFFER – A part or circuit used to reduce interaction between two electronic circuits.

BLOCK LEARN – ECM memory that adjusts the air/fuel ratio on a semipermanent basis.

BYTE – The number of “bits” that a computer processes as a unit.  Typically, a BYTE contains 8 BITS.

C3I – Computer Controlled Coil Ignition.  Produces the ignition spark without the aid of an ignition distributor.  Early term for Distributorless Ignition System.

CALIBRATION – Calibration Memory – The memory which contains an engine’s specific calibration.  The CALIBRATION is stored in the PROM chip.

CALIBRATOR – An electronic component which can be specifically programmed to meet engine operation requirements for each vehicle model.  It plugs into the Engine Control Module.

CALPAC – A device used with fuel injection to allow fuel delivery in the event of a PROM or ECM malfunction.

CAPACITOR (Condenser) – A device designed to hold or store an electric charge.

CATHODE – (1) The electron-emitting element of a vacuum tube.  (2) The negative electrode of a device.

CCC – Computer Command Control – Has an electronic control module to control air/fuel and emissions systems.

CCP – Controlled Canister Purge – An ECM controlled solenoid valve that permits fuel vapors stored in the charcoal canister to pass into the engine’s intake manifold.

CE – Check Engine – Lights when a malfunction occurs in the ECM system.

CID – Cubic Inch Displacement

CIRCUIT – The complete path provided for current flow.

CIRCUIT BREAKER – A device, other than a fuse, that automatically opens or breaks an overloaded circuit and can be reset manually or automatically.

CLOCK – A pulse generator in a digital computer which produces pulses to synchronize the switching circuit timing within the memory.

CLOSED CIRCUIT – A circuit which is uninterrupted from the current source and back to the current source.

COMMUNICATION – The transmission of information from one point, person, piece of equipment to another.

COMPUTER – Any device capable of accepting information, comparing, adding, subtracting, multiplying, dividing, and integrating this information and then supplying the results of these processes in proper form.

CONDUCTOR – Usually a wire or other metallic object made up of atoms whose free electrons are easily dislodged allowing easy electronic flow from atom to atom.

CONTACT – One of the current carrying parts of a relay, switch, or connector that engages or disengages to open or close electrical circuits.

CONTINUITY – A continuous path for the flow of an electrical current.

CATALYTIC CONVERTER – Contains platinum and palladium to speed up conversions of HC and CO, and rhodium to accelerate conversion of NOx.

CTS – Coolant Temperature Sensor – Device that senses the engine coolant temperature and passes that info to the ECM.

CO – Carbon Monoxide – One of the pollutants found in engine exhaust.

COUNTER – An electronic circuit that produces an output pulse each time a predetermined number of input pulses is received.

CURRENT – (Amperage) The rate of flow of electrons.

CYCLE – A complete sequence of a wave pattern that recurs at regular intervals.  The number of cycles which occur in one second is the frequency of the wave.

DATA – Information used as a basis for mechanical or electronic computation.

DIAGNOSTIC CODE – A code number used to describe a specific problem in an area of the entire computer control system aimed at helping the service technician identify the problem.

DIGITAL SIGNAL – An electrical signal that is either ON or OFF.

DIODE – An electronic device that allows current to flow in one direction only.

D.C. – Direct Current – An electrical current which flows in one direction only.

DIS – Direct Ignition System – Produces the ignition spark without the aid of an ignition distributor.  (Same as C3I).

DRIVER – An electronic device, usually a power transistor, that operates like a switch; that is, it turns something ON or OFF.

DVM – Digital Volt Meter – Used for precise measurement of voltage in electronic circuits.

DVOM – Digital Volt-Ohm Meter – Same as DVM but also can measure electrical resistance (OHMS).

DWELL – The amount of time that voltage passes thru a closed switch; for example, an internal switch in an electronic control module.

ECM – Electronic Control Module – A computer used to control engine components (outputs) based on signals it receives from sensors and switches (inputs).

EFI – Electronic Fuel Injection – Computer controlled fuel injection.

EGR – Exhaust Gas Recirculation – Method of reducing NOx emissions level.  Achieved by introducing exhaust gases into the intake manifold during certain periods of engine operation.

EMI – Electromagnetic Interference – An unwanted signal interfering with another needed signal that can cause problems with normal operation of an electronic device.

ENERGIZE – When current is passed thru an electronic device to turn it ON.

ESC – Electronic Spark Control – Used to modify spark advance when detonation occurs.

EST – Electronic Spark Timing – ECM controlled timing of ignition spark.

FREQUENCY – The number of cycles of a periodic phenomenon in a given unit of time, usually per second.

FUSE – A device containing a soft piece of metal which melts and breaks the circuit when it is overloaded.

FUSABLE LINK – The current carrying portion of a fuse which melts when the current is greater than a specified amount.

GROUND – A reference point from which voltage measurements may be made.  Also a return path for current flow back to the source.

HC – Hydrocarbons – One of the pollutants found in engine exhaust.

Hertz – (Hz) – A term meaning cycles per second used to describe frequency.

HIGH – A voltage more than ground or zero volts, like the output wire of an oxygen sensor is called “O2 high” as compared to its ground which is called “O2 low”.  In digital signals, high is ON and low is OFF.

IAC – Idle Air Control – A stepper motor installed in the throttle body of a Fuel Injected engine that the ECM uses to control the amount of air that is allowed to enter the engine at closed throttle (idle).

IGN – Ignition – Used to describe and Ignition circuit that gets power with the key in the RUN position.

Impedance – The total opposition a circuit offers to the flow of alternating current.  It includes resistance and reactance and is measured in Ohms.

INPUTS – Information for sources such as switches or sensors (ex: coolant temp, RPM, MAP).

INTEGRATOR – INT – Short Term Fuel Trim adjustment made by the ECM based on O2 sensor input.  Reacts more quickly than Block Learn (BLM) but is not stored in ECM memory.

INTERMITTENT – Occurs now and then, not continuously.

IP – Instrument Panel.

IPW – Injector Pulse Width – The amount of time the computer commands the injector to stay open and allow fuel flow.

MAF – Mass Air Flow.  Term used to describe the sensor on the engine that directly measures air flow entering the engine.

MALFUNCTION – A problem that causes the system to operate incorrectly.

MAP – Manifold Absolute Pressure.  Term used to describe the sensor on the engine that monitors manifold pressure (and vacuum).

MAT – Manifold Air Temperature.  Term used to describe the sensor on the engine that monitors manifold air temperature.

MEM-CAL – Memory Calibration Unit.  In 1986 and later cars, the MEM-CAL was introduced which was removable from the ECM that contained the PROM chip, limp-mode fuel chips (CAL-PAK), and sometimes the Knock Sensor Interface Module (depending on application).

MFI – Multi-Port Fuel Injection – Individual injectors for each cylinder mounted in the intake manifold.  The injectors are fired in groups (batch fire) rather than individually (as a sequential FI system).

MICRO – Prefix meaning one millionth.

MODE – Particular state of operation.

MPFI – same as MFI.

MULTIMETER – A test instrument used to measure voltage, resistance, and sometimes current and other electrical signals.

NC – Normally Closed – State of relay contacts when no voltage is applied to the relay; used to describe the circuit pathway of a relay circuit that permits current to flow with the relay off.

NO – Normally Open – State of relay contacts when no voltage is applied to the relay; used to describe the circuit pathway of a relay circuit that permits no current to flow with the relay off.

NOx – Nitrogen, Oxides of (NOx) – One of the pollutants found in engine exhaust caused by high combustion temperatures.  The EGR system reduces these emissions.

NON-VOLATILE MEMORY – Memory retained in block learn cells which is not affected or erased when the ignition key is turned off.

O2 Sensor – Oxygen Sensor – Monitors the oxygen content of the exhaust system and generates a voltage signal the ECM can interpret.

OPEN LOOP – Describes ECM control of the fuel delivery system when the O2 sensor information is ignored.

OUTPUT – A function or device controlled by the ECM.

PFI – Port Fuel Injection (same as MPFI)

P/N – Park/Neutral.

PROGRAM – The memory that includes the engine operating instructions.

PROM – Programmable Read-Only Memory – A term used to describe the chip used in the computer that contains the operating instructions and settings for the ECM.

PWM – Pulse Width Modulation – An electrical device operated by a digital signal the is controlled by the time duration the device is turned ON and OFF.

QDM – Quad Driver (Module) – A microchip that is capable of operating four separate outputs.

RELAY – A high current switch that is controlled by a low current electromagnetic coil.

RESISTANCE – The ability of a circuit to limit current flow, similar to a restriction in a water pipe.

RESISTOR – A device used in an electric circuit to produce work or to lower the voltage in a circuit.

RPM – Revolutions Per Minute – A measure of rotational speed.

RPO – Regular Production Option.

SFI – Sequential Fuel Injection – A port fuel injection system in which the injectors are fired one at a time in order precisely timed per intake valve open event.

TACH – Tachometer – A device used to measure RPM.

TBI – Throttle Body Injection – A fuel injection system where the fuel is injected before the throttle blade(s).

TCC – Torque Converter Clutch – An ECM controlled device (TCC solenoid) that engages a clutch inside of the torque converter that eliminates torque converter stall (slip) to improve fuel economy.

TPI – Tuned Port Injection – Used to describe a fuel injection system intake manifold that has runners tuned for peak engine performance during a given engine operating range.

TPS – Throttle Position Sensor – A device used to measure the position of the throttle.

V – VOLT.  Unit of measure for Voltage.

VACUUM – Negative pressure, less than atmospheric pressure.

VOLATILE MEMORY – Memory retained in the computer memory only when the ignition is ON.  Gets erased when the key is turned off.

VOLTAGE – The pressure or force pushing the current in a circuit; like pressure in a water pipe.

VSS – Vehicle Speed Sensor – A device used to measure vehicle speed; usually reported to the ECM, cruise control module, or speedometer in the form of digital pulses.

WOT – Wide Open Throttle

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