3 Cs A term used to describe the repair documentation process of 1st documenting the customer concern, 2nd documenting the cause of the problem, and 3rd documenting the correction.
accelerator pedal position (APP) sensor A potentiometer sensor that is attached to the accelerator pedal to signal the position of the pedal to the PCM
active fuel management (AFM) A General Motors cylinder deactivation system that collapses valve lifters to shut off cylinders.
active noise control (ANC) An Audi noise control system employed on its Valvelift system to mitigate the noises created by disabling cylinders.
after top dead center (ATDC) A point after top dead center.
aftermarket A company other than the original manufacturer that produces equipment or provides services.
amp clamp A tool used to measure amperage in a circuit. The tool is placed around the circuit conductor anywhere in the applicable circuit. The DMM will display a reading in mV, and this is multiplied by the factor selected on the tool. The result indicates the amount of amperage present in the circuit.
antilock brake systems (ABS) A safety measure for the braking system that uses a computer to monitor the speed of each wheel and control the hydraulic pressure to each wheel to prevent wheel lockup.
Atkinson-cycle engines Different than the Otto-cycle engine, holds the intake valve open longer to increase efficiency.
automotive stethoscope A tool that uses a long solid metal probe at the end that when held against a solid component transfers sound to the earpieces.
backpressure Pressure that is created in a sealed environment or in a restricted flow area.
barometric pressure (baro) sensor A sensor that measures atmospheric pressure.
before top dead center (BTDC) An event happening before the piston reaches its highest point in the cylinder.
bias voltage Voltage that has been created by the PCM to simulate a sensor that is not outputting a signal.
bidirectional tests The ability to command different solenoids and actuators on and off to check their operation.
BMW VANOS (variable nockenwellen steuerung) VVT from BMW that first appeared in 1992. The first version controlled only the intake camshaft. In 1996, dual VANOS was introduced, which controlled both camshafts. This is an oil-fed system that is electronically controlled to increase performance and decrease emissions.
calibrating A procedure performed to match electronic input and output values to ECM software.
calibration The software that operates the module and controls its outputs in the vehicle.
camshaft position (CMP) sensor A detection device that signals to the PCM the rotational position of the camshaft.
catalytic converter (CAT) Emission devices that help oxidize the exhaust as it flows out of the engine, to help reduce the hazardous emissions created by the combustion process.
cathode ray tube (CRT) A high-vacuum tube in which cathode rays produce a luminous image on a fluorescent screen, which are used chiefly in televisions and computer terminals.
cause Part of the 3Cs, documenting the cause of the problem. This documentation will go on the repair order, invoice, and service history.
center housing rotating assembly (CHRA) An assembly that consists of the turbine shaft, impeller, compressor wheels, and bearings that they rotate on.
charcoal canister (vapor canister) A device used to trap fuel vapors. Fuel vapors adhere to the charcoal until the engine is started, and engine vacuum can be used to draw (purge) the vapors into the engine so that they can be burned along with the air-fuel mixture.
closed loop (CL) The computer system receives feedback from various sensors to adjust engine operation.
coil oscillations The reading that determines whether the ignition coil has used all of its potential energy. This is shown on a digital storage oscilloscope (DSO).
coil pack A group of two or more ignition coils housed in one assembly.
coil-near-plug (CNP) An ignition coil that is near the spark plug and has a connection with a spark plug wire to connect it to the spark plug.
coil-on-plug (COP) An ignition coil that is mounted directly above the ignition coil. This type of ignition coil system has one coil for every cylinder.
component identification (CID) A component that is being tested within the TID.
compressed natural gas (CNG) Methane compressed for onboard storage in cylinders.
concern Part of the 3Cs, documenting the original concern that the customer came into the shop with. This documentation will go on the repair order, invoice, and service history.
conductors A material with low resistance for electron movement, used for current to flow in a circuit.
correction Part of the 3Cs, documenting the repair that solved the vehicle fault. This documentation will go on the repair order, invoice, and service history.
coupling A direct connection to the circuit that allows all frequencies to pass.
cranking cylinder compression test A test for the ability of a cylinder to create pressure that allows for combustion to happen.
crankshaft position (CKP) sensor A sensor used by the PCM to monitor engine speed. It can be one of three types of sensors—Hall-effect, magnetic pickup, or optical.
cursor A function that enables the user to measure quantity, time, and frequency between two points on the trace.
cylinder head temperature (CHT) sensor A sensor that changes resistance based on cylinder head temperature. It is in the cylinder head and does not touch coolant.
cylinder leakage test A test that measures the engine’s sealing ability and allows the technician to determine which cylinder has an internal issue.
cylinder power balance test A test that detects cylinder(s) that are causing a lack of power. It is also called a power balance test for short.
data link connector (DLC) The under-dash connector through which the scan tool communicates to the vehicle’s computers; it displays the readings from the various sensors and can retrieve trouble codes, Freeze Frame data, and system monitor data.
decoupler pulleys High-tech pulleys that provide belt-drive power to the alternator during acceleration and cruising speeds.
detonation When detonation occurs, the spark plug ignites the air-fuel mixture, as it should; however, the flame front initiated by the spark plug collides with an undesired flame front.
diagnostic trouble code (DTC) A code logged by the electronic control module when electrical faults or system problems occur in commercial vehicle control systems.
dielectric silicone compound grease A waterproof grease that is used to help seal the spark plug boot to the spark plug. Using silicone in the compound allows for high heat operation.
digital pressure feedback EGR (DPFE) sensor A sensor that takes a sample from the EGR pressure flow from the exhaust into the engine and monitors whether the EGR is operating or not allowing flow.
digital storage oscilloscope (DSO) A scope that displays voltage over a time, allowing the technician to see the signal. The DSO has a very fast refresh rate and is able to catch even the smallest signal error or fault. A DSO connects to a circuit in the same manner as using a DMM to measure available voltage. Technicians become skittish around the DSO because it requires setting the voltage and time scales to display the signal correctly. There are many other features, including data recording and setting a trigger to start or stop recording.
distributor cap The top portion of a distributor, used to make a connection between the spinning rotor and the HT leads.
distributorless ignition system (DIS) An ignition system that does not include a distributor. It uses signals from the CKP sensor and the CMP sensor sent to the PCM to determine when to send a signal to the ICM.
duty cycle The percentage of one period of time in which the circuit is powered on.
dwell The amount of time during which the primary circuit is grounded and current flows through the primary winding, building the magnetic field.
electrode gap The distance from the electrode to the grounding strap on a spark plug.
electromagnetic interference (EMI) A small electromagnetic field, which can interfere with other electronic devices because of the magnetic wavelengths produced; it is generated by every electronic device.
electromagnetism Magnetism that is created by running voltage through a coil.
electromotive force The pressure or push generated by any source of energy that causes electrons to flow in a conductor.
electronic control module (ECM) A computer that receives signals from input sensors, compares that information with preloaded software, and sends an appropriate command signal to output devices; it is used to manage the ABS.
electronic coolant temperature (ECT) sensor A sensor that changes resistance based on coolant temperature; it is also known as a thermistor.
electronic ignition (EI) systems An ignition system that uses a nonmechanical (electronic) method of triggering the ignition coil’s primary circuit.
electronic spark timing (EST) An ignition system that electronically controls spark timing, unlike a mechanical advance system.
electronically erasable programmable read-only memory (EEPROM) Nonvolatile memory technology that is used to store operating instructions or programming for an ECM.
engine coolant temperature (ECT) A thermistor that changes resistance as the temperature changes.
engine oil pressure (EOP) sensor A transducer type of sensor that is installed in an oil galley to change the fluid pressure into an electrical signal.
engine oil temperature sensor A thermistor type of sensor that is located in the oil pan to take the temperature of the oil.
EVAP vent valve A solenoid that allows fresh air to enter the evaporative system during a purge event. It is also used for an evaporative system monitoring test.
evaporative emissions (EVAP) control system A system used to capture vapors or gases from an evaporating liquid.
evaporative system integrity monitor (ESIM) A system that uses weighted check valves to determine the integrity of the EVAP system; it is simpler than an NVLD.
exhaust backpressure The amount of pressure that is present in an obstructed exhaust system.
exhaust gas recirculation (EGR) valve A valve that allows a controlled amount of exhaust gas into the intake manifold during a certain period of engine operation. It is used to lower NOx exhaust emissions.
Faraday’s law A law that states that a magnetic field induces a current in a conductor within that field.
firing line The tall lines on a parade pattern that indicate the voltage required to initially jump the spark plug gap.
Fischer-Tropsch process A process that changes a mixture of carbon monoxide gas and hydrogen gas into liquid hydrocarbons.
flashed A generic term of replacing or introducing the software necessary to make the control module operational.
forced induction The pressurization of airflow going into the cylinder through the use of a turbocharger or supercharger.
freeze frame data A snapshot of the conditions present when the DTC was stored. Refers to snapshots that are automatically stored in a vehicle’s powertrain control module (PCM) when a fault occurs (only available on model year 1996 and newer).
front-end accessory drive (FEAD) component Any front-end accessory drive component that is driven off of the front of the engine.
fuel cell An electrochemical device that uses hydrogen and oxygen to create electricity.
fuel pressure regulator A system that controls the pressure of fuel entering the injectors.
fuel pressure sensor A pressure transducer that measures the fuel pressure in the fuel rail.
fuel rail pressure (FRP) sensor A transducer type of sensor that is located on the fuel rail to send a signal to the PCM regarding the fuel pressure at that moment. It is usually found on returnless systems.
fuel tank pressure (FTP) sensor A sensitive pressure sensor mounted in the fuel tank or EVAP system and used to monitor the system for leaks.
gasoline A volatile, flammable liquid mixture of hydrocarbons, obtained from crude oil and used as fuel for internal combustion engines.
gasoline direct injection (GDI) A fuel-injection system in which fuel is sprayed directly into the combustion chamber.
Hall-effect switch A sensor commonly used to measure the rotational speed of a shaft. They have the advantage of producing a digital signal square waveform and have strong signal strength at low shaft rotational speeds.
helical phaser A type of phaser that has the gear teeth cut at an angle so that as the collar is pushed out, the inner gear, which is connected to the camshaft, rotates, thus rotating the camshaft. A splined phaser is oil fed, so the oil must be up to the recommended level.
high-density polyethylene (HDPE) A petroleum-based thermoplastic that is extruded to exact specifications of the application. The high strength to density ratio makes it ideal for use in the automotive environment.
high-pressure fuel sensor An electrical transducer on the high-pressure injection pump or the high-pressure fuel rail that gives feedback to the PCM to make fuel-injection decisions.
high-pressure injection pump A mechanical fuel pump that takes a low-pressure fuel charge and increases the pressure up to 3,000 psi (207 bar).
high-speed controller area network (HS-CAN) A wire data network in vehicles that is used to connect control modules so that they can communicate quickly and easily.
history DTCs Codes that were out of parameter at one time but are not currently out of range.
homogeneous charge compression-ignition (HCCI) engine A CI engine that uses gasoline for power instead of diesel fuel.
homogeneous operation mode A mode during which the PCM injects the fuel on the intake stroke to allow the air-fuel mixture to be evenly dispersed throughout the combustion chamber.
Honda VTEC (variable valve timing and lift electronic control) An oil-operated system, similar to VVT, that slides a pin to connect both rocker arms on one cylinder to a third rocker arm that is operating on a more aggressive duration. This system allows for the use of two different camshaft lobe designs on the same engine so that it can adapt to the needs of the driver.
horsepower An amount of work performed in a given time.
hot wire–type MAF sensor A type of mass airflow sensor that uses a wire in the airflow. A specific voltage is sent through the wire, and the PCM monitors the amperage that it takes to maintain the temperature of the wire. Using the amperage reading, the PCM can calculate the amount of air entering the intake manifold.
idle air control (IAC) motor A stepper motor–controlled idle motor that controls the air that bypasses the throttle blades to keep the engine running when the throttle is closed.
ignition control module (ICM) A general control unit in some electronic ignition (EI) systems, usually with current and dwell angle control; driver and output stage; and, in some cases, electronic spark timing functions.
inductance The property of a component that opposes the change of current flowing through it.
inductive probe A probe that creates a signal based on a magnetic pulse of which wire it is around.
inert gas A gas that does not undergo chemical reactions or change under different sets of conditions, such as temperature change.
intake air temperature (IAT) sensor A sensor that measures the temperature of the incoming air through the air filtration system.
intermittent faults A fault or customer concern that you can not detect all of the time and only occurs sometimes.
ionization A phenomenon that occurs when the coil’s high-voltage discharge across the spark plug gap causes the electrons in the air-fuel mixture to split and form a conductive path for current to flow.
Karman vortex MAF sensor Using air disturbance, this sensor can measure the volume of air that is going into the intake manifold.
keep alive memory (KAM) A series of battery-powered memory locations where the PCM stores information and data. The KAM uses a dedicated fused battery power circuit and ground to provide the power necessary to store the information. An example of KAM includes adaptive (learned) calibration strategies such as fuel trim, transmission shift points, and History or Continuous DTCs. This memory is retained as long as battery power is provided. Disconnecting the battery or low battery voltage will erase the memory, resetting the OBD II monitors and adaptive operating strategies.
lambda The ratio of air to fuel at which all of the oxygen in the air and all of the fuel are completely burned.
leak detection pump (LDP) A pump used on Chrysler products that compares the negative pressure in the EVAP system to the atmospheric pressure to determine the integrity of the EVAP system.
Lenz’s law A law that states that the induced current flows in the opposite direction from the initial change in current that produced the magnetic field.
liquefied natural gas (LNG) A cryogenic liquid produced from gaseous methane.
liquefied petroleum gas (LPG) Gaseous fuel at atmospheric pressure; commonly referred to as propane.
local interconnect network (LIN) A network designed by a consortium of automakers to provide the benefits of CAN but at a lower speed and lower cost. LIN uses a single-wire communication line.
long-term fuel trim (LTFT) A projected fueling need calculated by taking into account the operational situation of the engine. This is a learned value.
magnetic field The moving magnetic flux lines (field) induce a current in the secondary windings.
manifold absolute pressure (MAP) sensor A sensor that determines the amount of airflow based on the vacuum created by the engine.
mass airflow (MAF) sensor A sensor located in the air intake system that is used to measure the mass of the air flowing into the engine.
mass airflow (MAF) fuel management system A fuel-injection system that uses a MAF to measure the amount of airflow into the intake system.
Mercedes camtronic This system adjusts the intake valve lift based on engine load. Lift is changed mechanically by input of an electric motor controlled by the PCM.
Mode 6/Mode $06 One of the 10 modes of information from the OBDII emissions standards.
modules or nodes An electronic computer or circuit board that controls specific functions.
monitor identification (MID) A value within the OBDII emission standard system.
motor octane number (MON) A rating that is more severe operation than might be incurred at high speed or high load.
multiple displacement system (MDS) A Chrysler cylinder deactivation system employed on the Hemi engine family. This system limits the oil flow to four predetermined cylinders lifters, which allows them to collapse while turning off the ignition coil and injector to turn a V8 into a V4 engine.
natural vacuum leak detection (NVLD) pump A pump that uses the changing pressure of the fuel in the fuel tank to monitor whether it generates enough vacuum, which would indicate whether the system is in good condition.
Oersted’s law A law that states that a constant electric current flow generates a magnetic field around the conductor.
oil control valve (OCV) An electric solenoid that controls oil flow to the phaser on a valve train, which is controlled by the engine’s PCM.
on-board diagnostic systems 1 (OBD I) Systems operated under manufacturer standards, starting with California vehicles and becoming nationwide in 1981.
on-board diagnostic systems 2 (OBD II) Systems operated under standards set by the Society of Automotive Engineers (SAE) to conform with US Environmental Protection Agency (EPA) regulations starting in 1996.
open loop (OL) When the computer system feedback loop is not active.
operating as designed (OAD) A common situation in which the customer doesn’t understand how the vehicle operates.
optical switch A sensor that generates a voltage when excited by a beam of light.
original equipment manufacturer (OEM) The company that manufactured the vehicle.
oscilloscope (scope) A test instrument used to display a waveform of voltage over time on a screen. These offer much higher resolutions and sample rates than GMMs.
Otto four-stroke cycle A four-stroke cycle that includes intake, compression, combustion, and exhaust. It is the most commonly used cycle on an ICE.
output driver A device, usually a type of transistor, that controls an output device, such as the blower motor, an interior light, or a fuel injector.
oxides of nitrogen (NOx) Oxygen ions originating from nitric oxide (NOx) from among the other oxygen ions present in the exhaust gas.
oxygen (O2) sensor An exhaust sensor used to measure the amount of oxygen in the exhaust gases produced by the engine PCM, which it turn is used to determine fuel mixture and spark timing.
parade pattern The display of all the cylinders firing in sequence on an oscilloscope.
parameter identification (PID) A value or identifier of an item being reported with fault data.
pending DTCs Codes that failed the first monitor but have yet to fail a second monitor to become a hard code.
permanent DTCs Codes that require running the monitor associated with the code until it passes; it cannot be cleared with a scan tool.
permanent magnet (PM) sensor A sensor that uses metal passing by a magnet to generate an AC waveform to locate the position of a spinning component.
pickup coil A component with a wire coil wrapped around a ferrous metal core. It is used to generate an electrical signal when a magnetic field passes through it.
polarity The state of charge—positive or negative.
positive crankcase ventilation (PCV) valve A valve that controls the amount of crankcase ventilation flow that is allowed; it varies with changes in manifold pressure.
positive displacement pump Hydraulic pumps that have close internal clearances and will always move oil when they are turning.
potentiometer A three-terminal resistive device with one terminal connected to the input of the resistor, one terminal connected to the output of the resistor, and the third terminal connected to a movable wiper arm that moves up and down the resistor, creating a varying voltage signal. It is also called a pot or a variable resistor.
primary circuit The low-voltage circuit that turns the coil on and off.
pulse-width modulation (PWM) A digital on/off electrical signal. PWM is a very precise control method for an output device on a varying frequency. Usually, only fuel injectors are operated in this format, because the software programming and related circuits are very complex. Most other components are duty cycled on a fixed frequency.
random access memory (RAM) This is the section of the PCM that temporarily stores data. The RAM stores processed sensor information and temporary strategy-based results. The PCM can write to or read information from the RAM. When the ignition switch is turned OFF or battery power is removed from the PCM, all the stored RAM information is lost. The PCM will collect and store information in the RAM on the next key cycle.
read-only memory (ROM) Memory that is permanently stored inside a module. ROM is retained by the module even if the battery voltage is low or is disconnected. As the name suggests, information can only be read from the ROM. The PCM cannot write data to the ROM. ROM includes strategy calculation programs and vehicle-specific information such as tire size, axle ratio, transmission type, volumetric efficiency, and final gear ratio.
Reid Vapor Pressure (RVP) A measure of the volatility of gasoline.
relay An electromechanical switching device whose magnetism from a coil winding acts on a lever that switches a set of contacts.
repair order The document that is given to the repair technician that details the customer concern and any needed information.
research octane number (RON) A rating number that simulates fuel performance under low severity engine operation.
resistance The opposition to current flow through a conductor.
SAE J2534 standard The SAE standard that defines what type of interface is required to reprogram engine control units. This is a governmental regulation that allows non-OEMs to repair PCM-related emission issues.
scope channel The ability to measure different waveforms at the same time so that comparisons can be made between each channel.
secondary capacitance A condition that occurs when all the secondary components are pre-charged with the release of high energy from the secondary coil windings just before the spark plug gap ionizes and the plug fires.
secondary circuit The part of an ignition system that operates on higher voltage and delivers the necessary high voltage to the spark plug.
service advisor The person at a repair facility that is in charge of communicating with the customer.
service history A complete listing of all the servicing and repairs that have been performed on that vehicle.
short fuel trims (SFT) A calculated measurement based on fuel pressure and oxygen (O2) sensor readings, which controls the amount of fuel that is introduced into the engine.
short-term fuel trim (STFT) A calculation that determines the amount of fuel the engine is using and adjusts it based on the upstream oxygen sensor signal.
smog A type of air pollution that includes oxides of nitrogen, sulfur oxides, ozone, smoke, and dirt particles that create a fog over an area.
spark line The duration of the burn time, which is a direct result of the coil’s reserve and secondary resistance.
spark plug A plated metal shell with a ceramic insulator, a resistor, and an electrode that extends through the center of the insulator, a side electrode, and an air gap.
spark plug wire High-voltage wiring that transmits power from the distributor or ignition coil to the spark plug.
spark-ignition (SI) engine This type of engine operates with a spark plug to start the combustion process.
speed density fuel management system A fuel-injection system that does not use a MAF sensor to measure airflow into the intake but instead a combination of TP, MAP, ECT, and O2 sensors to calculate airflow.
stepper motor A specialized DC motor that has a rotor operated by a series of coils that surround the rotor. The rotor is stepped, or moved incrementally, by pulsing the coils in sequence, causing the rotor to move in a specific direction and amount of rotation. The coils can be pulsed in either direction, so the rotor can move clockwise or counterclockwise. These motors are often used to move a component a very specific amount for precise control of the related output system, like the doors in heating and air conditioning duct work.
stoichiometric ratio Optimal ratio of fuel to air that causes all of the fuel to burn, gasoline’s optimal ratio is 14.7:1.
stoichiometry The relationship between the relative quantities of substances taking part in a reaction or forming a compound.
strategy-based diagnostic process A systematic process used to diagnose faults in a vehicle.
stratified charge mode A layering of a lean air-fuel mixture in the combustion chamber. It is used when the fuel injector and piston head place fuel near the spark plug but not the surrounding space.
supercharger A component that uses external power to turn the compressor wheel to compress the air as it enters the intake system. The supercharger is usually driven by a belt off the crankshaft or directly from an electric motor.
supplemental restraint systems (SRS) A passenger safety system, such as airbags and seat belt pretensioners.
symptom-to-system-to-component-to-cause (SSCC) A process that provides an organized logical approach to diagnostics.
technical service bulletin (TSB) Information, released frequently by manufacturers, on parts updates, service procedures, module-programming updates (reflashing), wiring concerns, or normal system operation, instructing the technician that no repair attempt is needed.
test identification (TID) An identification number of test within the OBDII emission standard system.
thermistor A variable resistor that changes its resistance based on temperature. Most thermistors have a NTC, meaning that their resistance decreases as temperature increases. Commonly used to measure coolant, oil, fuel, and air temperatures.
throttle actuator control (TAC) motor A stepper motor that opens and closes the throttle blades to control engine acceleration, replacing the throttle cable. This is controlled by the PCM, which gets input from various sensors on the vehicle.
top dead center (TDC) The very top of the stroke of the piston in a cylinder, where the piston cannot move any higher.
torque A measurement of the twisting, or rotational, force of an object.
Toyota VVT-iE (variable valve timing with intelligence by electric motor) A system controlled by an electric motor on the end of the camshaft. By using an electric motor, low oil level or pressure doesn’t affect system performance.
transducer An electrical device that creates an electrical signal based on a pressure input and displays it graphically on a lab scope.
transistor A semiconductor device usually made with three layers of doped silicon material. Bipolar transistors can be constructed as positive-negative-positive (PNP) or negative-positive-negative (NPN) types. A transistor has a base, collector, and emitter. A small current at the base controls a larger current through the collector and emitter. The emitter is denoted by an arrow, which usually points toward the ground portion of the circuit.
transmission fluid temperature (TFT) sensor A type of variable resistor used inside the transmission to monitor oil temperature.
trigger A setting on a DMM, GMM, or DSO that starts or stops a recording or signal display event. The trigger usually has several options that allow one-time or repeat functions.
triggering circuit The triggering device produces the signal to the ICM or PCM for coil switching. This circuit uses the device to turn a coil on and off.
turbocharger A forced induction device driven by exhaust gas pressure and used to compress intake air so that more air can be pushed into the cylinders, creating more power.
two-stroke engine An engine that has a power cycle every other stroke.
vacuum The opposite of pressure. Any pressure less than atmospheric is a vacuum.
valve overlap The time when both valves are open as the piston travels in the bore.
vane airflow (VAF) sensor A type of MAF sensor that uses a spring-loaded door attached to a potentiometer to signal a position of the door to the PCM. The airflow moves the door, and the PCM uses this reading to generate a CFM reading.
vane-type phaser A type of phaser that operates with a set of paddles inside the assembly. When oil pressure is applied to one side of the paddles, it rotates the camshaft inside the phaser; to reverse the rotation, it applies oil pressure to the opposite side of the paddles.
variable displacement engine (VDS) An engine that can change the volume (cubic inches or liters) of displacement through cylinder deactivation or a mechanical means.
variable geometry turbocharger (VGT) A type of turbocharger that is adjustable by directing exhaust gases toward or away from the exhaust impeller. This is a common way to control the turbocharger more precisely in order to match the requirements of the engine.
variable nozzle turbocharger (VNT) A type of turbocharger that uses nozzles to adjust the exhaust gases toward different areas of the exhaust impeller to increase power—usually two exhaust passages.
variable turbine geometry (VTG) Another name used by certain manufactures for the VGT.
variable valve lift (VVL) A system employed on an engine to change the amount of lift of the valve based on input from the PCM.
variable valve timing (VVT) The ability of an engine to change the advance or retard of a camshaft or camshafts to match the requirements of the engine performance level.
vehicle emission control information (VECI) The VECI decal is located under the hood in a variety of locations, such as on top of the core support, on a strut tower, or on the underside of the vehicle hood. The decal lists the installed emission control devices, the year the vehicle’s emission system conforms to, and which OBD system is used.
vehicle speed sensor (VSS) A sensor used by the PCM to measure vehicle speed. It is often located in the transmission extension housing. The output signal may be analog or digital.
venturi vacuum A condition in which airspeed has to increase when air passes through a tube that narrows.
volumetric efficiency (VE) A ratio, given as a percentage, of the amount of air-fuel mixture that is drawn into the cylinder as compared to the displacement of the cylinder.
wide-band oxygen sensor A more complex oxygen sensor that gives the PCM an exact measurement of the air-fuel ratio. This sensor uses voltage supplied by the PCM to generate a signal based on exhaust oxygen content.
zirconia oxygen sensor An oxygen sensor that uses zirconia metal to generate a voltage based on different gases that flow past the sensor.