Automotive terms Modern (P-Q)

Automotive Technical terms and abbreviations overview used in the industry, Guide and explanations.

The following are examples of Mid to Modern technical terms recommended for general use worldwide. For in-depth specific terms also see terms for historic vintage and specific areas such as Paint.

PARALLEL CIRCUIT:
(See circuit, parallel.)

PARTS WASHER:
A basin or tub, usually with a built-in pump mechanism and hose used for circulating chemical solvent for the purpose of cleaning greasy, oily and dirty components.

PART-TIME FOUR WHEEL DRIVE:
A system that is normally in the two wheel drive mode and only runs in four-wheel drive when the system is manually engaged because more traction is desired, Two or four wheel drive is normally selected by a lever to engage the front axle, but if locking hubs are used, these must also be manually engaged in the Lock position,
Otherwise, the front axle will not drive the front wheels.

PASSIVE RESTRAINT:
Safety systems such as air bags or automatic seat belts which operate with no action required on the part of the driver or passenger. Mandated by Federal regulations on all vehicles sold in the U.S. after 1990.

PAYLOAD:
The weight the vehicle is capable of carrying in addition to its own weight. Payload includes weight of the driver, passengers and cargo, but not coolant, fuel, lubricant, spare tire, etc.

PCM:
Powertrain control module.

PCV VALVE:
A valve usually located in the rocker cover that vents crankcase vapors back into the engine to be reburned.

PERCOLATION:
A condition in which the fuel actually "boils," due to excessive heat. Percolation prevents proper atomization of the fuel causing rough running.

PICK-UP COIL:
The coil in which voltage is induced in an electronic ignition.

PING:
A metallic rattling sound produced by the engine during acceleration. It is usually due to incorrect ignition timing or a poor grade of gasoline.

PINION:
The smaller of two gears. The rear axle pinion drives the ring gear which transmits motion to the axle shafts.

PINION GEAR:
The smallest gear in a drive gear assembly.

PISTON:
A disc or cup that fits in a cylinder bore and is free to move. In hydraulics, it provides the means of converting hydraulic pressure into a usable force. Examples of piston applications are found in servo, clutch, and accumulator units.

PISTON RING:
An open-ended ring which fits into a groove on the outer diameter of the piston. Its chief function is to form a seal between the piston and cylinder wall. Most automotive pistons have three rings: two for compression sealing; one for oil sealing.

PITMAN ARM:
A lever which transmits steering force from the steering gear to the steering linkage.

PLANET CARRIER:
A basic member of a planetary gear assembly that carries the pinion gears.

PLANET PINIONS:
Gears housed in a planet carrier that are in constant mesh with the sun gear and internal gear. Because they have their own independent rotating centers, the pinions are capable of rotating around the sun gear or the inside of the internal gear.

PLANETARY GEAR RATIO:
The reduction or overdrive ratio developed by a planetary gearset.

PLANETARY GEARSET:
In its simplest form, it is made up of a basic assembly group containing a sun gear, internal gear, and planet carrier. The gears are always in constant mesh and offer a wide range of gear ratio possibilities.

PLANETARY GEARSET (COMPOUND):
Two planetary gearsets combined together.

PLANETARY GEARSET (SIMPLE):
An assembly of gears in constant mesh consisting of a sun gear, several pinion gears mounted in a carrier, and a ring gear. It provides gear ratio and direction changes, in addition to a direct drive and a neutral.

PLY RATING:
A rating given a tire which indicates strength (but not necessarily actual plies). A two-ply/four-ply rating has only two plies, but the strength of a four-ply tire.

POLARITY:
Indication (positive or negative) of the two poles of a battery.

PORT:
An opening for fluid intake or exhaust.

POSITIVE SEALING:
A sealing method that completely prevents leakage.

POTENTIAL:
Electrical force measured in volts; sometimes used inter- changeably with voltage.

POWER:
The ability to do work per unit of time, as expressed in horsepower; one horsepower equals 33,000 ft. lbs. of work per minute, or 550 ft. lbs. of work per second.

POWER FLOW:
The systematic flow or transmission of power through the gears, from the input shaft to the output shaft.

POWER-TO-WEIGHT RATIO:
Ratio of horsepower to weight of car.

POWERTRAIN:
see Drivetrain.

POWERTRAIN CONTROL MODULE (PCM):
current designation for the engine control module (ECM), In many cases, late model vehicle control units manage the engine as well as the transmission. In other settings, the PCM controls the engine and is interfaced with a TCM to control transmission functions.

PPM:
Parts per million; unit used to measure exhaust emissions.

PREIGNITION
Early ignition Of fuel in the cylinder, sometimes due to glowing carbon deposits in the combustion chamber. Preignition can be damaging since combustion takes place prematurely.

PRELOAD:
A predetermined load placed on a bearing during assembly or by adjustment.

PRESS FIT:
The mating of two parts under pressure, due to the inner diameter of one being smaller than the outer diameter of the other, or vice.

PRESSURE:
The amount of force exerted upon a surface area.

PRESSURE CONTROL SOLENOID (PCS):
An output device that provides a boost oil pressure to the mainline regulator valve to control line pressure. Its operation is determined by the amount of current sent from the PCM

PRESSURE GAUGE:
An instrument used for measuring the fluid pressure in hydalic circuit

PRESSURE REGULATOR VALVE:
In automatic transmissions, its purpose is to regulate the pressure of the pump output and supply the basic
fluid pressure necessary to operate the transmissions The regulated fluid pressure may be referred to as mainline pressure, line pressure, or control pressure.

PRESSURE SWITCH ASSEMBLY (PSA):
Mounted inside the transmission, it is a grouping of oil pressure switches that inputs to the PCM when certain hydraulic passages are charged with oil pressure.

PRESSURE PLATE:
A spring-loaded plate (part of the clutch) that transmits power to the driven (friction) plate when the clutch is engaged.

PRIMARY CIRCUIT:
The low voltage side of the ignition system which consists of the ignition switch, ballast resistor or resistance wire, bypass, coil, electronic control unit and pick-up coil as well as the connecting wires.

PROFILE:
Term used for tire measurement (tire series), which is the ratio of tire height to tread width.

PROM (PROGRAMMABLE READ-ONLY MEMORY):
The heart of the computer that compares input data and makes the engineered program or strategy decisions about when to trigger the appropriate output based on stored computer instructions.

PULSE GENERATOR:
A two-wire pickup sensor used to produce a fluctuating electrical signal. This changing signal is read by the controller to determine the speed of the object and can be used to measure transmission/transaxle input speed, output speed, and vehicle speed.

PSI:
Pounds per square inch; a measurement of pressure.

PULSE WIDTH DUTY CYCLE SOLENOID (PULSE WIDTH MODULATED SOLENOID):
A computer-controlled solenoid that turns on and off at a variable rate producing a modulated oil pressure; often referred to as a pulse width modulated (PWM) solenoid. Employed in many electronic automatic transmissions and transaxles, these solenoids are used to manage shift control and converter clutch hydraulic circuits.

PUSHROD:
A steel rod between the hydraulic valve lifter and the valve rocker arm in overhead valve (OHV) engines.

PUMP:

A mechanical device designed to create fluid flow and pressure buildup in a hydraulic system.

QUARTER PANEL:
General term used to refer to a rear fender. Quarter panel is the area from the rear door opening to the tail light area and from rear wheel well to the base of the trunk and roof-line.