Abbreviations and Glossary of Terms
ACL - AIR CLEANERProvides preheated air to outer intake manifold to provide better driveability when engine is cold.
A/F
Air/Fuel Ratio
AIR - SECONDARY AIR INJECTION
Air flow from pump is directed into engine to reduce exhaust emissions.
CO - CARBON MONOXIDE
One of the pollutants found in engine exhaust.
CRANK ANGLE SENSOR
The crank angle sensor is built into the distributor and is a photo electric pick-up sensor. This senses crankshaft position and engine speed.
DIAGNOSTIC "TEST" TERMINAL
Lead of the data link connector which is grounded to flash diagnostic trouble codes through the malfunction indicator lamp.
DTC - DIAGNOSTIC TROUBLE CODE
Pair of numbers obtained from flashing the malfunction indicator lamp (MIL) or displaying on a "Scan" Tool. These numbers paired together are used to determine which part of the emission control system is malfunctioning.
DLC - DATA LINK CONNECTOR
Used at the assembly plant to evaluate the control module system and for service to flash the malfunction indicator lamp to ensure proper control module system operation. Also used to read serial data from ECM.
DVM (10 Megaohm)
Digital Voltmeter with 10 million ohms resistance - used for measuring voltages and resistances within the control module system.
DWELL
The amount of time (recorded on a dwellmeter in degrees of crankshaft rotation) that voltage passes through a closed switch; for example, ignition contact points or internal switch within the engine control module.
ECM - ENGINE CONTROL MODULE
A metal cased box (located within the passenger compartment containing electronic circuitry which electrically controls and monitors air/fuel and emissions systems on the control module system, and lights the malfunction indicator lamp when a malfunction occurs in the system.
ECT - ENGINE COOLANT TEMPERATURE
The temperature of the engine coolant.
ECT SENSOR
The engine coolant temperature sensor is a thermistor which relays engine coolant temperature information to the engine control module. This temperature sensor is used as one of the criteria to determine when the system is ready to enter the closed loop mode of operation. The information from this sensor is also used to modify the open loop duty cycle and AIR control.
EGR - EXHAUST GAS RECIRCULATION
A method of reducing NOx emission levels.
EGR DUTY SOLENOID (CALIFORNIA EMISSIONS ONLY)
This sensor is located next to the EGR valve from the vacuum regulator in accordance with ECM control.
EGR TEMPERATURE SENSOR (CALIFORNIA EMISSIONS ONLY)
This sensor is located immediately next to the EGR valve, in the recirculated exhaust gas passage between the EGR valve and the intake manifold, and detects EGR system malfunctions.
ENERGIZE/DE-ENERGIZE
When voltage is passed through the duty solenoid, the metering control armature is pulled into the solenoid (energized). When the voltage to the solenoid is turned off, a spring raises the metering control armature (de-energized).
EVAP - EVAPORATIVE EMISSIONS SYSTEM
Used to prevent gasoline vapors in the fuel tank from entering the atmosphere.
FED - FEDERAL
Vehicle/engine available in all states except California.
HC - HYDROCARBONS
One of the pollutants found in the engine exhaust.
HO2S - HEATED OXYGEN SENSOR
The HO2S monitors the oxygen content of the exhaust system and generates a voltage signal to the ECM as oxygen content rises (lean mixture) voltage decreases; and as the oxygen content decreases, (rich mixture) voltage increases.
IDEAL MIXTURE
The air/fuel ratio which provides the best performance, while maintaining maximum conversion of exhaust emissions, typically 14.7/1.
INPUTS
Information from sources (ECT sensor, 02S, etc.) that tells the ECM how the engine is performing.
INTERMITTENT
Occurs now and then; not continuously. In electrical circuits, refers to occasional open or short.
L-4
Four cylinder in-line engine.
MALFUNCTION
A problem that causes the system to operate incorrectly. Typical malfunctions are: failed sensors, duty solenoids, PROM failure and wiring harness open circuits or shorts.
MASS AIR FLOW SENSOR
The mass air flow sensor is a hot wire type; it senses the air flow rate and sends a voltage signal to the ECM.
MFI - MULTIPORT FUEL INJECTION
Individual fuel injectors for each cylinder are mounted in the intake manifold. The injectors are fired in groups rather than individually to increase cold start-up performance.
MIL - MALFUNCTION INDICATOR LAMP
The electronic engine control system utilizes a light within the instrument cluster which, for some failure modes, will inform the driver of the need for unscheduled maintenance. In the event of a system malfunction, the MIL will light and remain lit as long as the fault condition is present and the engine is running. The engine control module (ECM) incorporates a diagnostic program which will assist in diagnosing closed loop operation control system discrepancies. When activated, the diagnostic program will flash any DTCs through the MIL, which isolates the source of the system failure.
MAP
Manifold absolute pressure.
MAP SENSOR
The vacuum sensor is linked up to the ECM and, together with the vacuum switch output, senses fully closed (idle) and wide open throttle (WOT) conditions of the throttle valve.
MODE
A particular state of operation.
N.C.
Normally closed - State of relay contacts or solenoid plunger when no voltage is applied.
N.O.
Normally open - State of relay contacts or solenoid plunger when no voltage is applied.
NOx - NITROGEN, OXIDES OF (NOx)
One of the pollutants found in engine exhaust.
OPEN LOOP
Describes ECM control of the duty solenoid without use of the O2S information.
OUTPUT
Functions, typically by solenoids, that are ECM controlled.
PCV - POSITIVE CRANKCASE VENTILATION
Prevents fumes in the crankcase from escaping into atmosphere.
RPM - REVOLUTIONS PER MINUTE
A measure of rotational speed.
SELF-DIAGNOSTIC MODE
The ECM can detect malfunctions within the electronic engine control system. If a malfunction occurs, the ECM lights a malfunction indicator lamp (MIL). A technician can access, or obtain diagnostic trouble codes (DTCs) through the MIL. The DTCs that are emitted will indicate the area of the malfunction.
TP - THROTTLE POSITION
The position of the throttle plate and lever.
TVV - THERMAL VACUUM VALVE
Used to control vacuum in relationship to engine temperature.
TWC - THREE-WAY CATALYTIC CONVERTOR
Exhaust convertor containing platinum to speed up conversions of HC and CO, and rhodium to accelerate conversion of NOx.
VACUUM
Negative pressure; less than atmospheric pressure.
VACUUM, MANIFOLD
Vacuum source in manifold below throttle plate.
VACUUM, PORTED
A vacuum source in the manifold below the throttle plate.
VACUUM REGULATOR
A device that regulates constant EGR signal vacuum.
VACUUM TANK
Stores vacuum in case of the sudden shortage of signal vacuum under various engine conditions.