Chapter 6
Glossary of Terms

With the introduction of computer control, a lot of new technologies have been making their way into transmission operation... and into their diagnosis and repair.

Along with these new technologies have come a number of terms. Some of these terms may be familiar; some others may not.

To help you understand these units better, we’ve put together this glossary. It includes many of the terms and acronyms that appear in this program, along with terms you may run into elsewhere while diagnosing or repairing these transmissions.

If you’re unsure of a term, always look it up; if you can’t find it here, check your shop manual. But the important thing is, don’t guess. Make sure you understand the information before investing your time and money into a diagnosis or repair.

A

Airbag — Also SIR; Supplemental Inflatable Restraint. Protective device designed to inflate on impact to protect driver and passengers from harm.

 

Ammeter — Electrical test device that measures current flow in a circuit. Displays measurement in amperes, or amps.

 

Amperage — Measurement of current flow in a circuit.

 

Amperes; Amps — Unit of measurement for reading current flow. Amperage is actually a reading of how many electrons are moving through a circuit at any given moment. One amp is the amount of current that one volt will push through one ohm of resistance.

 

Amperes; Amps — Unit of measurement for reading current flow. Amperage is actually a reading of how many electrons are moving through a circuit at any given moment. One amp is the amount of current that one volt will push through one ohm of resistance.

 

Analog Meter — Measurement device that provides readings using a needle, instead of a digital output. Analog meters measure constantly, so the reading you see is the value taking place right now. But analog meters tend to be less accurate than digital meters, and the reading only updates as quickly as the needle can move.

 

ASD Relay — Automatic Shutdown Relay. Chrysler’s device for providing power to its computer control systems.

B

B+ — Battery power.

C

Closed Circuit — A complete electrical path that provides the means for electricity to perform work. A closed circuit allows current to flow from its source, through the resistances, and back to its source.

 

Coast Clutch — The coast clutch engages to provide engine braking during manual operating ranges.

 

Computer — Also controller; microprocessor. Device that provides the commands necessary to operate the engine or transmission, based on inputs from a series of sensors and switches.

 

Continuous Memory Codes — Ford’s term for diagnostic trouble codes that remain in memory, whether the problem’s there now or not. Also known as "hard" codes.

 

Controller — See Computer.

 

Conventional Electrical Theory — Electrical circuit model which indicates that electrical flow is from positive to negative. More recent studies show that electrons actually flow from negative to positive, but most texts still prefer to use the conventional model.

 

Current — Electron flow through a circuit, current is measured in amps.

D

De-energize — To turn off, or shut down a circuit or component.

 

Diagnostic Trouble Codes — Numerical codes that provide information about problems or failures in a computer system. Designed to help identify problems in a computer system.

 

Digital — On/off signal. A series of pulses that are either on or off, which provide information by varying frequency, or which control a circuit by varying frequency, duty cycle or on-time.

 

Digital Multimeter — Also DMM; DVOM; Digital Volt-Ohmmeter. Electrical device that provides measurements of electrical circuits, using a digital display. Digital meters and oscilloscopes read a circuit through sampling; how accurate your measurement is depends on how many samples the meter takes per second.

 

Digital Volt-Ohmmeter — See Digital Multimeter.

 

Distributorless Ignition System — Also Electronic Ignition. A type of ignition that doesn’t use a distributor to provide spark to the cylinders. These systems usually provide spark through a process known as "wastespark"; a process which provides spark to two cylinders at once. One cylinder fires; the other receives spark on its exhaust stroke — that cylinder’s spark is "wasted." Ford uses this term to identify one of its electronic ignition system.

 

Diode — An electrical one-way shutoff valve. A diode is a semiconductor, designed to allow current flow in one direction, but not in the other direction. These devices are commonly used to control the spark that develops when an electromagnetic coil de-energizes, and the magnetic field collapses.

 

Duty Cycle — A signal that varies its relationship between on-time and off-time. Duty cycle signals usually control a computer output device, such as an electronic pressure control solenoid: The longer the signal on-time, the longer the solenoid remains open, so the lower mainline pressure becomes.

E

Electrostatic Discharge — Electrical potential that releases suddenly; the "shock" you feel when you touch a doorknob on a dry day is electrostatic discharge. That "shock" can damage or destroy electronic components. That’s why it’s important to take precautions — wear a static strap, never touch the terminals, etc. — when working with electronic devices.

 

Energize — To turn on a circuit or component; provide with power and ground, to enable an electrical device to operate.

 

Engine Control Module — Also ECM. SAE J-1930 term for a device that controls only engine operation. See also PCM, TCM, Computer.

F

Failsafe — Backup mode; sometimes called "limp-in" or "limp home" mode. This is a reduced function mode that provides enough capability to get off the road and back home. In failsafe, all of the solenoids are off, and, if the system controls pressure electronically, it’ll be at maximum level.

 

Force Motor — GM’s term for an electronic pressure control solenoid.

 

Frequency — The number of complete oscillations, or cycles, that occur each second. Measured in Hertz.

G

Ground — The return side of an electrical circuit, as defined by the conventional electrical theory. More recent studies show that electrons actually flow in the opposite direction of that shown by conventional theory, but it’s still the most common model for electrical circuits.

 

Grounded Circuit — An electrical circuit failure that keeps the circuit energized all the time, regardless of switch or relay position. Also known as a short-to-ground.

H

Hertz — Also Hz. Unit of measurement for frequency; the number of complete cycles that take place in one second. A signal that repeats itself 20 times every second has a frequency of 20 Hertz.

 

High Impedance — Having high resistance to electrical flow. Usually used to describe electrical meters. When used to test an electronic circuit, a low impedance meter would affect the characteristics of the circuit. The higher the meter’s impedance, the less effect it will have on the circuit, so the less change it will make to the circuit operation when connected.

I

Intermittent — Taking place in an irregular or unpredictable cycle. An intermittent problem or failure may happen one moment, then not be there the next. That’s why intermittent failures are often difficult to isolate.

K

Keep-Alive Memory — Battery power that enables the computer system to retain its memory, even after the key is turned off. On many vehicles, disconnecting the battery will erase the keep-alive memory.

L

Latch — Ford’s term for connecting the self test input terminal to ground. This signals the computer to begin a phase of the self test display.

 

Light-Emitting Diode — Also LED. A semiconductor that lights when energized, much like a light bulb. But, unlike a light bulb, an LED requires very little current, and that current flow must be in a specific direction, or the LED won’t light.

M

MAF Sensor — Mass Airflow Sensor. A device that provides the computer with a voltage or frequency signal based on the amount of air entering the engine. The computer uses this signal to determine vehicle load.

 

Malfunction Indicator Lamp — Also MIL. SAE J-1930 term for the light on the instrument panel that indicates a problem in the computer system. Used to be called the "check engine" light, "service engine soon" light, or "power loss" light.

 

MAP Sensor — Manifold Absolute Pressure sensor. This potentiometer measures intake manifold vacuum as compared with absolute zero pressure, and then modifies a voltage signal to indicate that pressure to the computer. The computer uses this signal to determine vehicle load.

 

Microprocessor — See Computer.

O

Ohm — Unit of resistance measurement. It takes one volt to push one amp of current through one ohm resistance.

 

Ohmmeter — Electrical device for measuring resistance in a circuit or component.

 

Ohm’s Law — Principle that defines the relationship between pressure (voltage), flow (amperage) and resistance (ohms). Ohms x Amps = Volts; Volts ¸ Ohms = Amps; Volts ¸ Amps = Ohms.

 

On-Demand Codes — Ford’s term for diagnostic trouble codes that are only available while the problem is occurring; these codes won’t remain in memory after the failure is gone. Also known as "soft" codes.

 

Open Circuit — An incomplete electrical path that won’t provide the means for electricity to perform work. An open circuit prevents current flow, so the circuit won’t operate.

 

Oscilloscope — An electrical test device that maps voltage changes in a circuit over a specific amount of time. An oscilloscope displays the voltage signal as a picture, to show how voltage changes through the component’s operating cycle.

 

Overdrive — A gear ratio lower than 1.0:1. This ratio increases output shaft RPM beyond the input shaft RPM, while lowering the torque delivered. Most automatic transmissions and transaxles deliver overdrive operation above third gear.

 

Oxygen Sensor — An electrical device that provides a voltage signal to the computer based on the oxygen content in the exhaust. The computer uses this signal to monitor the engine’s air/fuel mixture, to keep it operating as efficiently as possible, while keeping emissions as low as possible.

P

Potentiometer — A three-wire sensor that modifies a voltage signal based on movement or position. Potentiometers receive a regulated voltage signal to one end of a resistor, and ground to the other; a wiper slides along the resistor, and picks up the voltage signal, based on its position along the resistor.

 

Powertrain Control Module — Also PCM. SAE J-1930 term for a computer that controls engine and transmission operation. A PCM may also control other systems, including cruise control, A/C system, antilock brakes, etc., but it must control engine and transmission to be called a PCM. See also ECM, TCM.

 

Pulse Generator — An AC generator that develops a frequency signal that varies with the rotational speed of an internal transmission component, such as a sun shell, turbine shaft or output ring gear. The computer uses this signal to measure the component’s RPM. From this, the computer can determine when a shift is complete or if a clutch is slipping.

 

Pulse Width Modulated — Also PWM. A signal that varies its relationship between on-time and off-time. Pulse width modulated signals usually control a computer output device, such as an electronic pressure control solenoid: The longer the signal on-time, the longer the solenoid remains open, so the lower mainline pressure becomes. See Duty Cycle.

R

Relay — An electrical device that allows a low current circuit to control a high current circuit. Energizing a relay energizes an electromagnet, which opens or closes a set of contacts, to provide power or ground to a circuit that would normally require too much current for the device controlling the circuit.

 

Resistance — The ability of a circuit or device to reduce or limit current flow.

 

Resistor — A device that limits or reduces current flow in a circuit.

S

Scan Tool — A device that enables you to retrieve information directly from the vehicle computer system, and translates that information into readings you can interpret and understand.

 

Self Test Input — Also STI. Ford terminal that enables you to signal the computer to display diagnostic trouble codes. Ford vehicles enter different test modes, depending on whether you latch (ground) or unlatch (unground) the STI terminal.

 

Self Test Output — Also STO. Ford terminal the computer uses to deliver diagnostic trouble code information pulses, and serial data for scan tool communication.

 

Sensor — A device that provides signals to the computer, based on engine operating conditions. The computer uses these signals to control engine operation more precisely.

 

Serial Data — A digital signal from the computer, to communication information with other computers or scan tools. Scan tools can provide the actual sensor readings the computer sees, and outputs from the computer, by interpreting serial data signals.

 

Short Circuit — An electrical circuit without the resistance necessary to operate properly. Because of this lost resistance, these circuits will often burn up, unless protected by a fuse or circuit breaker. Not to be confused with a grounded circuit.

 

Shrink Tubing — An insulating material that shrinks to seal a connection when you apply heat.

 

Signal Monitor — A device you can build to let you watch the actual shift signals from the computer to the transmission.

 

Solenoid — An electrical device that turns electrical signals into movement or work. Solenoids can control lever movement, such as throttle kickers, or can control vacuum or hydraulic flow. The solenoids you’ll most likely be dealing with open and close to control hydraulic flow, to allow the transmission to shift gears, control lockup, and control line pressure.

T

Thermistor — A semiconductor that varies resistance based on temperature. There are two types of thermistor: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). The NTC thermistor is more common — as the temperature goes up, its resistance goes down.

 

Throttle Position Sensor — A potentiometer that modifies a voltage signal based on the position of the vehicle’s throttle plate. The computer uses this signal to determine vehicle load.

 

Transistor — A semiconductor that operates as an electronic "relay." Transistors allow a low current circuit to control power or ground to a high current circuit.

 

Transmission Control Module — Also TCM. SAE J-1930 term for a device that controls only transmission operation. See also PCM, ECM, Computer.

U

Unlatch — Ford’s term for removing the ground wire from the self test input terminal.

V

Variable Resistor — A one- or two-wire sensor that modifies a voltage signal based on stress or temperature. Thermistors are the most common type of variable resistor in today’s cars and trucks.

 

Vehicle Speed Sensor — An electrical device that enables the computer to monitor vehicle speed. These sensors are either optical (early GM), mechanical switches (usually imports, such as Toyota), or AC frequency (most vehicles today).

 

Voltage — The pressure in an electrical system, that pushes current through the circuit. One volt of pressure is necessary to push one amp of current through one ohm of resistance. Sometimes called the circuit’s potential.

 

Voltmeter — Electrical test device that measures the voltage potential in a circuit. Displays its reading in volts.

W

Wiggle Test — Ford-specific test for looking for loose connections in a circuit. A wiggle test includes wiggling the wires, connectors and components, to see whether an intermittent problem appears.

 

ACRONYMS

3–2 T/CCS — 3–2 Timing/Coast Clutch Solenoid. This is a dual function solenoid; it controls the shift timing for the 3 – 2 downshift, and also controls operation of the coast clutch in manual gear ranges.

A/C — Air Conditioning

ALCL — Assembly Line Communication Link

ALDL — Assembly Line Data Link

BCM — Body Control Module

C3I — Computer Controlled Coil Ignition

CAL-PAK — Calibration Package

CCS — Coast Clutch Solenoid.

CTS — Coolant Temperature Sensor

DFI — Digital Fuel Injection

DIS — Distributorless Ignition System; Electronic Ignition.

DMM — Digital Multimeter.

DPDIS — Dual Plug Distributorless Ignition. Ford ignition system that appears on some 2.3 engines, from 1989 to 1992.

DPFE — Differential Pressure Feedback EGR. An electrical sensor that measures the difference in pressure between the EGR ports, to allow the computer to determine whether the EGR is operating, and providing adequate flow.

DTC — Diagnostic Trouble Code.

DVOM — Digital Volt-Ohmmeter.

ECM — Engine Control Module.

EDIS — Electronic Distributorless Ignition System. A specific Ford electronic ignition system that uses an AC-generating sensor to determine crankshaft position.

EEPROM — Electronically-Erasable Program Read-Only Memory. The PROM is a computer chip that provides vehicle-specific information to the computer, to enable it to control vehicle operation properly. An EEPROM can be erased and reprogrammed electrically, through the diagnostic link connector. This enables the manufacturer to provide updates to the computer system, without an additional parts investment.

EFI — Electronic Fuel Injection. System designed to control fuel deliver to the engine, through a series of electronic solenoids, called "injectors."

EGR — Exhaust Gas Recirculation valve. Device designed to recirculate exhaust gas into the vehicles intake, to reduce the burn rate. This controls cylinder temperature, which, in turn, reduces NOx production.

EI — Electronic Ignition; See Distributorless Ignition System.

EOT — Engine Oil Temperature

EPC — Electronic Pressure Control. A system that controls transmission mainline pressure with an electrical solenoid. The computer provides the solenoid with a duty cycle signal — the longer the solenoid is energized, the lower mainline pressure will be.

EPROM — Erasable Program Read-Only Memory. The PROM is a computer chip that provides vehicle-specific information to the computer, to enable it to control vehicle operation properly. An EPROM can be erased with ultraviolet light, and then reprogrammed electrically. EPROMs usually have a small piece of tape covering the light-sensitive cell — never remove that tape, unless you’re planning to erase the EPROM.

EST — Electronic Spark Control

EVP — EGR Valve Position sensor. A potentiometer that measures the EGR valve pintle, to determine whether the valve is opening properly. Only measures the valve — doesn’t measure the actual flow through the system.

FI — Fuel Injection

FMEM — Failure Mode Effects Management. Ford’s term for failsafe operation; a backup strategy that takes over when a failure affects system operation.

Hz — Hertz.

IAC — Idle Air Control

IAT — Intake Air Temperature

ISC — Idle Speed Control

KAM — Keep-Alive Memory.

KOEO — Key On, Engine Off. Ford’s term, now accepted by the industry to describe a test mode in which the system is receiving ignition power, without the engine running.

KOER — Key On, Engine Running. Ford’s term to indicate the engine is running. This usually means engine idling, unless indicated otherwise.

LED — Light-Emitting Diode.

MAF — Mass Air Flow

MAP — Manifold Absolute Pressure

MAT — Manifold Air Temperature

MCCC — Modulated Converter Clutch Control. This is one type of system used to control pressure to the converter clutch circuit, which enables the computer system to control the feel of the converter clutch apply.

MEM-CAL — Memory Calibration, PROM

MIL — Malfunction Indicator Lamp.

NPN — Negative-Positive-Negative. A type of transistor that provides ground for a circuit based on an voltage signal.

O2 — Oxygen

OBD-II — On-Board Diagnostics, Version Two. A series of monitors and self diagnostics designed to provide reduced vehicle emissions. Introduced nationwide in 1994, all gas-powered vehicles were required to meet OBD-II standards by 1996.

PCM — Powertrain Control Module.

PFE — Pressure Feedback EGR. An electrical sensor that measures the pressure in the EGR outlet, to allow the computer to determine whether the EGR is operating, and providing adequate flow.

PFI — Port Fuel Injection

PIP — Profile Ignition Pickup. Ford’s term for the electrical signal from the crankshaft sensor that indicates crankshaft position and RPM. From this signal, the computer system controls ignition operation and timing.

PNP — Positive-Negative-Positive. A type of transistor that delivers power to a circuit based on a ground signal.

PROM — Program Read Only Memory. A computer chip that provides vehicle-specific information to the computer, to enable it to control vehicle operation properly.

PWM — Pulse Width Modulated.

QDM — Quad Driver Module

RAM — Random Access Memory. A type of computer memory that enables the computer to process conditions that occur during vehicle operation. RAM is the scratchpad for computer operation: It’s where the computer records what’s going on in the system, and where it makes ongoing changes and corrections to system operation.

ROM — Read Only Memory. This is where the computer stores its basic programming, to control system operation. Lookup tables and operating parameters are stored in ROM, for comparison to actual operating conditions.

SFI — Sequential Fuel Injection

SPOUT — Spark Output signal. Ford’s term for the signal from the computer that provides the ignition module with the dwell and timing information necessary to control the ignition properly. The computer develops the SPOUT signal from the PIP signal.

STI — Self Test Input.

STO — Self Test Output.

TCC — Torque Converter Clutch. Friction clutch inside the torque converter that locks the turbine shaft to the converter lid, to remove all slip from the converter. Eliminates the heat developed through torque multiplication.

TCM — Transmission Control Module.

TFT Sensor — Transmission Fluid Temperature sensor. A variable resistor that modifies a voltage signal to provide the computer will a measurement of transmission fluid temperature.

TOT — Transmission Oil Temperature sensor. A variable resistor that modifies a voltage signal to provide the computer will a measurement of transmission oil temperature.

TPS — Throttle Position Sensor.

VATS — Vehicle Antitheft System

VCC — Viscous Converter Clutch

VSS — Vehicle Speed Sensor.

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