Glossary of terms

Some times we come across a word that we don’t know what it means, That is why I typed out this glossary to help make things easier when finding out, and understand, what is wrong , or what something is.

Not all terms used in here will be used in just Jeeps, but it has many you will find or hear when figuring out what it wrong, or what something is on your Jeep. As I find more terms we will add them here.

0-9:

A:

A/C:

Air conditioning

A/F:

Air/Fuel ratio. The proportion of air and fuel delivered to the cylinder for combustion. For example, an A/F ratio of 14:1 denotes 14 times as much air as fuel in the mixture. A typical A/F ratio is 14.7:1

AC Clutch Relay:

The PCM uses this relay to energize the A/C clutch, turning the A/C system on or off.

AC Pressure Sensor:

Measures air conditioning refrigerant pressure and sends a voltage singal to the PCM

AC Pressure Switch:

A mechanical switch connected to the A/C refrigerant line. The switch is activated (sending a signal to the PCM) when the A/C refrigerant pressure becomes too low.

Actuator:

Actuators such as relays, solenoids, and motors allow the PCM to control the operation of vehicle systems.

Air Injection Reaction (AIR) System:

An emission control system operated by the PCM. During cold starts, an air pump injects outside air into the exhaust manifold to help burn hot exhaust gases. This reduces pollution and speeds warm-up of oxygen sensors and catalytic converters. After the engine is warm, the air will either be “dumped” back into the atmosphere (or into the air cleaner assembly) or sent to the catalytic converter.

B:

Bank 1:

The standard way of referring to the bank of cylinders containing cylinder #1. Inline engines have only one bank or cylinders. Most commonly used to identify the location of oxygen sensors.

Bank 2:

The standard way of referring to the bank of cylinders opposite cylinder #1. Found on V-6, V-8, V-10, ect. And horizontally opposed engines. Most commonly used to identify the location of oxygen sensors.

BARO:

Barometric Pressure Sensor, See MAP Sensor.

Boost control solenoid:

A solenoid that is energized by the PCM, in order to control supercharger boost pressure.

Brake Switch Signal

An input singal to the PCM indicating that the brake pedal is being pressed. The singal is typically used to disengage cruise control systems and Torque Converter Clutch (TCC) solenoids.

C:

CAM:

Camshaft Position Sensor. Sends a frequency singal to the PCM in order to synchronize the fuel injector and spark plug firing.

CARB:

California Air Resources Board. Governing body for emissions control in California.

CKP REF:

Crankshaft Position Reference.

CKP:

Crankshaft Position. See CPS.

Closed Loop (C/L):

A feedback system that uses the O2 Sensor(s) to monitor the results of combustion. Based on the singal(s) from the O2 sensor(s), The PCM modifies the air/fuel mixture to maintain optimum performance with lowest emissions. In closed loop mode, the PCM can “fine tune” control of a system to achieve an exact result.

CO:

Carbon Monoxide.

Continuous Memory Codes:

See Pending codes.

CPS:

Crankshaft position sensor. Sends a frequency singal to the PCM. It is used to reference fuel injector operation and synchronize spark plug firing on distributor less ignition systems (DIS)

CTS:

Coolant Temperature Sensor. A resistance sensor that sends a voltage singal to the PCM indicating the temperature of the coolant. The singal tells the PCM whether the engine is “cold” or “warm”.

D:

Data Link Connector (DLC):

The interface port between the vehicle’s on-board computer and a diagnostic tool. Vehicles with OBD II use a 16 pin connector located in the Passenger compartment.

Data Stream:

The actual data communications sent from the vehicle’s PCM to the data connector.

DEPS:

Digital Engine Position Sensor.

Detonation:

See Knock.

DTC:

Diagnostic Trouble Code. Indicates a malfunction flagged by the vehicle’s computer.

DI/DIS:

Direct Ignition/Distributorless Ignition System. A system that produces the ignition spark without the use of the distributor.

Duty Cycle:

A term applied to signals that switch between “on” and “off”. Duty cycles is the percentage of time the signal is “on”.

E:

ECT:

Engine Coolant Temperature sensor.

EFI:

Electronic Fuel Injection. Any system where a computer controls fuel delivery to the engine by using fuel injectors.

EGR:

Exhaust Gas Recalculation. The PCM uses the EGR system to recalculate exhaust gases back into the intake manifold to reduce emissions. EGR recalculation is used only during warm engine cruise conditions. EGR flow at other times can cause stalling or no starts.

EPA:

Environmental Protection Agency.

ESC:

Electronic Spark Control. An ignition system function that warns the PCM when “Knock” is detected. The PCM will then retard spark timing to eliminate the knocking condition.

EST:

Electronic Spark Timing. An ignition system that allows the PCM to control spark advance timing. The PCM determines optimum spark timing from sensor information, engine speed, throttle position, coolant temp, engine load, vehicle speed, Park/Neutral switch position, and knock sensor condition.

EVAP:

Evaporative Emissions System.

F:

G:

H:

Hall Effect Sensor:

Any of a type of sensor utilizing a permanent magnet and a transistorized Hall effect switch. Hall Effect type sensors may be used to measure speed and position of the crankshaft or camshaft – for spark timing and fuel injector control.

HO2S:

Heated Oxygen Sensor

I:

IAC:

Idle Air Control. A device mounted on the throttle body which adjusts the amount of air bypassing a closed throttle so that the PCM can control idle speed.

ICM:

Ignition Control Module.

I/M:

Inspection and Maintenance.

ISC:

Idle Speed Control. A small electric motor mounted on the throttle body and controlled by the PCM. The PCM can control idle speed by commanding the ISC to adjust its position.

J:

K:

Knock:

Uncontrolled ignition of the air/fuel mixture in the cylinder. Also referred to as detonation or ping. Knock indicates extreme cylinder pressures or “hotspots” which are causing the air/fuel mixture to detonate prematurely.

Knock Sensor (KS):

Used to detect engine detonation or “Knock.” The sensor contains a piezoelectric element and is threaded into the engine block. Special construction makes the element sensitive only to engine vibrations associated with detonation.

KOEO:

Key on, engine off.

KOER:

Key On, Engine Running.

L:

LCD:

Liquid Crystal display.

LT:

Long Term Fuel Trim.

M:

M/T:

Manual Transmission or manual transaxle.

MAF:

Mass Air Flow Sensor. Measures the amount and density of air entering the engine and sends a frequency or voltage signal to the PCM. The PCM uses this signal in its fuel delivery calculations.

MAP:

Manifold Absolute Pressure Sensor. Measures intake manifold vacuum or pressure and sends a frequency or voltage singal (depending on sensor type) to the PCM. This gives the PCM information on engine load for control of fuel delivery, spark advance, and EGR flow.

MAT:

Manifold Air Temp Sensor. A resistance sensor in the intake manifold that sends a voltage singal to the PCM indicating the temperature of the incoming air.The PCM uses this singal for fuel delivery calculations.

MIL:

Malfunction Indicator Lamp. The MIL is most commonly know as the check engine light. Also labeled Service engine soon, Power loss or power limited.

Monitor:

A test performed by the on-board computer to verify proper operation of emission related systems or components.

MPFI or MFI:

Multi-Port Fuel Injection. MPFI is a fuel injection system using one (or more) injector(s) for each cylinder. The injectors are mounted in the intake manifold, and fired in groups rather than individually.

N:

Nox:

Oxides of Nitrogen. A pollutant. The EGR system injects exhaust gases into the intake manifold to reduce these gases at the tailpipe.

O:

O2S:

Oxygen sensor. Generates a voltage of 0.6 to 1.1 Volts when the exhaust gas is Rich (Low oxygen content). The voltage changes to 0.4 volts or less when the exhaust gas is lean (high oxygen content). This sensor only operates after it reaches a temp of approximately 349 deg C (660 Deg F). O2 sensors are usually found both upstream and downstream of the catalytic converter The PCM uses these sensors to fine tune the air-fuel ratio and to monitor the efficiency of the catalytic converter.

ODM:

Output Device Monitor.

OBD II:

On-board Diagnostics, second gen. OBD II is a U.S. Government mandated standard requiring all cars and light trucks to have a common data connector, connector location, communication protocol, DTSs and Code definitions. OBD II First appeared on vehicles in late 1994, and is required to be present on all cars sold in the US after January 1, 1996.

Open Loop (O/L):

A control system mode that does not monitor the output to verify if the desired results were achieved. A fuel delivery system will usually operation open loop mode during cold engine warm-up because the oxygen sensors are not yet ready to send a signal. Without the oxygen sensor signal, the computer cannot check the actual results of combustion.

P:

P/N:

Park/Neutral switch. This switch tells the PCM when the gear shift lever is in the Park or Neutral position. When in Park or Neutral, the PCM will operate the engine in an “idle” mode.

PCM:

Powertain control Module. The “Brians” of the engine control system housed in a metal box with a number of sensors and actuators connected via a wiring harness. Its job is to control fuel delivery, idle speed, spark advance timing, and emissions systems. The PCM receives information from sensors, then energizes various actuators to control the engine. The PCM is also known as the ECM (Engine Control Module).

PROM:

Programmable Read-only Memory. The PROM contains Programming information the PCM needs to operate a specific vehicle model/engine combination.

Pending Codes:

Also referred to as Continuous Memory codes and Maturing Diagnostic Trouble codes. These codes are set when intermittent faults occur after a certain number of drive cycles, the code is erased from memory.

Purge Solenoid:

Controls the flow of fuel vapors from the carbon canister to the intake manifold. The canister collects vapors evaporating from the fuel tank, preventing them from escaping to the atmosphere and causing pollution. During warm engine cruise conditions, the PCM energizes the purge solenoid so the trapped vapors are drawn into the engine and burned.

Q:

R:

Reluctance Sensor:

A type of sensor typically used to measure crankshaft or camshaft speed and/or position, drive shaft speed, and wheel speed.

ROM:

Read-only Memory. Permanent programming information stored inside the PCM, containing the information the PCM needs to operate a specific vehicle model/engine combination.

S:

SAE:

Society of Automotive Engineers.

Sensor:

Any device that reports information to the PCM. The job of the sensor is to convert a parameter such as engine temp into an electrical singal that the PCM can understand.

Sensor 1:

A standard term used to identify the location of oxygen sensors. Sensor 1 is located upstream of the catalytic converter.

Sensor 2:

A standard term used to identify the location of oxygen sensors. Sensor 2 is located downstream of the catalytic converter.

SFI or SEFI:

Sequential Fuel Injection or Sequential Electronic Fuel Injection. A fuel injection system that uses one or more injectors for each cylinder. The injectors are mounted in the intake manifold, and are fired individually.

ST:

Short Term Fuel Trim.

T:

TBI:

Throttle Body Injection. A fuel injection system having one or more injectors mounted in a centrally located throttle body, as opposed to positioning the injectors close to an intake valve port. TBI is also called Central Fuel Injection (CFI) in some vehicles.

TDC:

Top Dead Center. When a piston is at its uppermost position in a cylinder.

Throttle Body:

A device which performs the same function as a carburetor in a fuel injection system. On a throttle body injection (TBI) system, the throttle body is both air door and the location of the fuel injectors. On port fuel injection systems (PFI, MPFI, SFI, ect.) the throttle body is simply an air door. Fuel is not added until the injectors at each intake port are activated. In each case, the throttle body is attached to the accelerator pedal.

TPS:

Throttle Position Sensor. Potentiometer-type sensor connected to the throttle shaft. Its voltage singal output increases as the throttle is opened. The PCM uses this singal to control many systems such as idle speed, spark advance, fuel delivery, ect.

TTS:

Transmission Temp Sensor. A resistance sensor mounted in the transmission housing in contact with the transmission fluid. It sends a voltage singal to the PCM indicating the temp of the transmission.

U:

V:

VECI:

Vehicle Emission Control Information. A decal located in the engine compartment containing information about the emission control systems found on the vehicle. The VECI is the authoritative source for determining whether a vehicle is OBD II compliant.

VIN:

Vehicle identification number. This is the factory assigned serial number. This number’s stamped on a number of locations throughout the vehicle, but the most prominent location is on the top of the dashboard on the drive’s side, visible from the outside. The VIN includes information about the vehicle, including where it was built, body and engine codes, options, and sequential build number.

VSS:

Vehicle Speed Sensor. Sends a frequency singal to the PCM. The frequency increases as the vehicle moves faster to give the PCM vehicle speed information used to determine shift points, engine load, and cruise control functions.

W:

WOS:

Wide-Open Throttle. The vehicle operating condition brought about when the throttle is completely (or nearly) open. The PCM will typically deliver extra fuel to the engine and de-energize the A/C compressor at this time for acceleration purposes. The PCM uses a switch or the throttle Position Sensor to identify the WOT condition.

X:

Y:

Z: