A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
P
P/N: Park and neutral position switch for sending signals to the PCM.
P/S: Power Steering Pressure Switch. Also PSP switch.
Pan: Alternative name for a sump.
Panel Lights: Illumination for instruments and other displays.
Panhard Rod: Rear axle transverse link between the chassis and axle beam. It is used to hold the axle in relation to the body during cornering or for sideways forces.
Parallel: The condition that exists when the centre lines of two or more items or components or lines do not converge. The extended lines in both directions will always remain at an equal distance apart.
Parallel Circuit: Electrical circuit with all components connected in their own individual circuits so that if one fails the others remain in operation.
Parking Brake: Mechanical system of braking to hold vehicle stationary.
Parking Gear: The component(s) in an automatic bo that lock the drive when 'Park' is selected.
Particulates: Exhaust pollution consisting of very small particles of matter (soot) that are produced as a by-product of combustion. Seen as smoke in a vehicle exhaust, particularly from diesel engines.
PAS: Power Assisted Steering.
Pascal (Pa): Standard unit of pressure (N/m2) named after a scientist who studied pressure in liquids. Pascal's principle of the transmission of pressure in fluids established that the pressure in a completely filled container is equally applied throughout and any change in pressure is transferred to all parts of the fluid and walls of the container.
Passive Restraint: Safety features of a vehicle that act only in an accident. Seat belts, head restraints, air bags and pre-tensioners are examples.
Pawl: Part of the ratchet mechanism that holds the ratchet. A pivoted tooth that engages in the teeth of the ratchet wheel to either prevent the pawl lever or the wheel from rotating in one direction only or in some mechanisms to drive the wheel forward.
PCM: Powertrain Control Module.
PCV: Positive Crankcase Ventilation. A series of pipes and valves connecting the engine crankcase to the inlet manifold or air cleaner in order to reduce oil vapour emission to atmosphere.
Perceptual Safety: A reference to how safe the driver and passengers feel.
Perishing: Description of how some components, particularly if rubber-based, can decay.
Perpendicular: At ninety degrees to another plane or line.
Petrol: Volatile hydrocarbon fuel for spark ignition engines. Also gasoline.
Petroleum Jelly: A type of grease used for battery terminals. Vaseline is a refined version.
PFI: Port Fuel Injection.
PG: Pulse Generator.
Phase: The time span between the start and end of a single wave moving from zero to positive and negative positions and returning to zero.
Phase Sensor: Sensor that indicates camshaft position and hence where the engine is in its cycle.
Phosphor bronze: A material that can absorb oil making it ideal for making bushes/bearings.
Photoelectric: The generation of an electrical current by light shining on certain materials such as some semiconductor devices. Photoelectric cell, photodiode or phototransistor.
Phototransistor: A transistor that is operated by light.
Pick Up Pipe: Oil pipe that picks up oil from the oil pan.
Piezo-resistive: A special crystal that changes resistance as pressure is applied.
Piezoelectric: Voltage produced by shock waves on a piezo crystal. Used in engine knock sensors.
Pilot Bearing: Small bearing usually where two shafts meet. See also Spigot.
Pinging: Noise heard from an engine when the ignition of fuel occurs too early (advanced) in the cycle. Also 'ping'.
Pinion: A small gear wheel or the driver of a meshing pair of gear wheels.
Pinion Gear: A small gear wheel or the driver of a meshing pair of gear wheels.
Pinion Shaft: A shaft on which a small gear runs.
Pinking: Noise heard from an engine when the ignition of fuel occurs too early (advanced) in the cycle. Also 'ping'.
Pintaux: Type of injector for an indirect injection engine. Similar to pintle but with additional small injection orifice for low engine speeds.
Pintle: Type of injector for an indirect injection engine. Uses a spring-loaded needle that is raised by fuel pressure to allow a spray of fuel to enter the pre-combustion chamber.
PIP: Profile Ignition Pick Up Signal.
Pipe Union: A joint in a pipe.
Piston: Reciprocating component, usually in the form of a cylinder closed at one end, that operates under fluid pressure within a smooth walled cylinder. In a reciprocating engine, gas pressure on the piston crown provides the prime force that is converted into rotating mechanical power by the crankshaft.
Piston Blow: Term used to describe gases blowing past the piston rings.
Piston Crown: The top of the piston.
Piston Ring: Sealing rings usually made of cast iron. Fitted on to a piston to make a gas tight seal.
Pitch: (1) Distance that two points are apart. Examples are thread dimensions and pitch circle diameters of concentric drillings. (2) Vehicle body movement from back to front or from front to back.
Pitman Arm: The output arm on a steering gearbox. Also known as a drop arm.
Pitting: Surface damage caused by localized corrosion or erosion.
Pivot Bolt: A simple bolt on which something pivots (turns).
Pivot Point: The point about which something pivots!
Planet Carrier: Frame with spindles that the planet gears rotate on as part of an epicyclic gear set.
Planetary Gears: Gears that rotate around sun gears (differential, epicyclic gearing, etc.)
Plastigauge: Brand name of a product that is used to determine bearing clearance.
Plate Grids: Basket like holders to contain the active material in a battery.
Plate Lug: A connection point on the battery plate.
Plenum: A chamber in the air inlet system to provide even air supply to all cylinders.
Plies: Rayon cords used in tyre construction.
Plug Thread: Screwed thread that is designed for a spark plug.
Plunge
Plunger: Alternative term for a piston or needle in a pump, slave cylinder or injector.
Ply (Tyre): Fabric layer used in the construction of a tyre.
Ply Rating: Load rating of a tyre.
Pneumatic: Transfer of force by air or gas.
Pneumatic Suspension: Suspension system using air or gas springs.
Points: The switching contacts of an ignition contact breaker.
Polarised Light: Light that has been filtered so that its rays oscillate only in one direction.
Polarity: A description of a component that must have positive and negative connections connected correctly.
Polarity (Electrical): Electrical positive and negative charges.
Polarity (Magnetic): Magnetic north and south poles.
Polarized Light: Light that has been filtered so that its rays oscillate only in one direction.
Pole: The ends of a magnet where the field lines are emitted.
Pollution: Products or by-products that destroy purity or make environments foul or filthy.
Polypropylene: Manmade plastic material used for electrical insulation, bumpers and other trim components.
Poppet Valve: Conventional inlet and exhaust valves having a circular plate at right angles to a central stem that runs through a guide tube.
Porosity: Property of a material that allows fluid to soak into or through it.
Port: Hole or aperture shaped to facilitate the flow of gas or liquid into or from a chamber. Usually denoted by its function, as inlet port or exhaust port.
Port Fuel Injection: Petrol electronic fuel injection system with injectors in each inlet manifold spraying fuel in towards the inlet valves in the ports of each cylinder. Also known as multipoint injection.
Position Switch: A switch used to feedback position of a moving component.
Positive Camber: Steering geometry where the road wheel leans outward at the top.
Positive Castor: Angle in side elevation between the steering and vertical axis. Steering axis hits the ground in front of the vertical axis.
Positive Crankcase Ventilation: A series of pipes and valves connecting the engine crankcase to the inlet manifold or air cleaner in order to reduce oil vapour emission to atmosphere.
Positive Displacement: A term applied to pumps which transfer liquid in the same quantity as the volume in the pumping chamber for each action of the pump.
Positive Offset (Wheel): The position of the wheel nave or disc when outside the centre line of the wheel.
Positive Scrub: Positive scrub radius steering geometry where a line through the steering swivel axis meets the road surface inside of the tyre centre line.
Positive Temperature Coefficient: Type of resistor that has resistance increasing with increases in temperature. The normal response for metal conductors. These resistors are used in electrical circuits to give temperature sensing and control.
Potential: Energy stored in a stationary object or chemical combination that has the capacity to do work.
Potential Difference: Difference of electric potential between points (p.d) volts.
Potentiometer: A variable resistor with manual operation that provides an output voltage from a sliding terminal on a resistor block.
Pounds Feet: Old unit of torque. Also foot pounds. Torque is now given in the SI units of Newton metres Nm.
Pour Point: Applied to fuel oils (diesel) to indicate the temperature where it will still flow under its own weight. The pour point specified value is 3 degrees above the point where it will only just flow.
Power: The rate of doing work. It is measured by the standard unit called the watt (W) and is equal to one joule per second. This is a very small unit and kilowatt (kW) or megawatt (MW) is more often used. Also, Horsepower which is the old term for power.
Power Assisted Steering: The use of a hydraulic or electrical system to increase the driver's effort on the steering wheel thus reducing the effort that the driver has to apply.
Power Booster: Hydraulic or pneumatic brake pedal or hydraulic pressure booster.
Power Distribution: A central point from which various components are supplied.
Power Output: Power developed by an engine.
Power Stroke: Part of the four-stroke cycle following combustion.
Powertrain: Term used to describe the engine, transmission and driveline components as a unit.
PPM: Parts Per Million
Pre-ignition: Spontaneous ignition in a petrol engine that occurs before the controlled ignition point. Can be caused by an overheated engine, incandescent particles in the combustion chamber or incorrect fuel.
Preignition: Spontaneous ignition in a petrol engine that occurs before the controlled ignition point. Can be caused by an overheated engine, incandescent particles in the combustion chamber or incorrect fuel.
Preload: Additional tightening of a bearing or component after the backlash or free play has been eliminated. Used to eliminate backlash after the bearings have bedded in. Usually set by a Nm or angular torque.
Pressure: Pressure is the product of a force multiplied by the area on which the force is applied. The standard unit of pressure is the Pascal which is equivalent to one N/m2.
Pressure Bleeder: A brake/clutch bleeder that forces fluid through the system.
Pressure Cap: Cap used to pressurise cooling system.
Pressure Chamber: An area used to hold a pressure as something expands of to supply pressure.
Pressure Charged: An engine using a pressure-charger to boost the air charging pressure above atmospheric pressure, to increase the air mass entering the cylinders of the engine.
Pressure Conscious: Variable opening valve used for sensing and adjusting the pressure in brake circuits to restrict force to the rear brakes.
Pressure Differential: The difference in pressures between two sides of a component or areas in a system that are used to operate the component or system. Atmospheric pressure is often used in conjunction with a vacuum to provide a force.
Pressure Gauge: An instrument for measuring pressure of a fluid or a gas.
Pressure Modulator: A device for controlling pressure in a system.
Pressure Plate: Component of the clutch.
Pressure Regulator: A valve in a hydraulic system that controls line pressure.
Pressure Relief Valve: The valve in an oil or hydraulic circuit that opens to release excess fluid pressure and return fluid to the feed side of the pump.
Pressure Switch: A pressure sensitive switch used to provide a signal voltage to an instrument, lamp or electronic control module.
Pressure Wave Supercharger: A supercharger using the exhaust pressure waves to boost the inlet air pressure. This supercharger uses a drum with longitudinal drillings that is rotated in time with the engine and ported to match inlet and exhaust pressure waves together.
Primary Shoe: A brake shoe that has a leading edge making first contact when applied. Also leading shoe.
Primary Winding: The low tension (primary circuit) coil of wire in an ignition coil.
Primer: A base paint between metal and top coat.
Priming: Lifting fuel into the system components to remove air.
Priming Pump: A manually operated pump that lifts fuel into the system.
Progression: Initial acceleration of the throttle after the idle position. Going onward/upward.
Progressive Carburettor: Usually a carburettor with two chokes, the second of which only opens as the throttle is pushed further down.
PROM: Programmable Read Only Memory.
Propellor Shaft: Connects gearbox to final drive and transmits torque on rear wheel and four wheel drive vehicles.
Proportioner Valve: A valve used in hydraulic brake circuits to split the force between the front and rear brake circuits.
Propshaft: Connects gearbox to final drive and transmits torque on rear wheel and four wheel drive vehicles.
Propshaft
Propulsion: Application of a driving force.
Proton: One of a number of particles in the nucleus of an atom. The proton has a positive polarity and is electrically positive in opposition to the negative charge of the electons.
Prototype: A working version of a new design.
PS: The German word for horsepower. Pferdestärke. 1PS equals 0.986bhp.
Psi: Pound per square inch. A measure of pressure in old units. The SI unit of pressure is the Pascal (Pa).
PSPS: Power Steering Pressure Switch.
PT: Part Throttle.
PTO - Power Take Off: A supplementary drive from a vehicle transmission that is used to drive to auxiliary units.
Pull-in Winding: A winding in a starter motor solenoid that actuates the solenoid to pull the switch contacts together. It is often earthed through the armature so that the drive pinion rotates as it moves into mesh with starter ring gear.
Pull-off Spring: A simple return spring to open or close something after it is switched off.
Puller: A tool for applying a pulling force. For example, to remove a gear from a shaft.
Pulleys: Used to transmit or receive drive from a belt. The alternator pulley is a good example.
Pulsation: On/off or increase/decrease in pressure or position.
Pulsation Damper: Any device, such as a hydraulic accumulator, for damping pulsations in a fluid system, as for example the pressure pulses from a fuel pump.
Pulse: A change in electrical or mechanical signal.
Pulse Air Injection: An emission control system that uses exhaust pressure pulsations to draw air into the exhaust gas flow to increase the available oxygen in the catalytic converter.
Pulse Generator: Inductive electronic device that provides information to the ignition amplifier or ECU on engine position.
Pulse Shaping: The action carried out in an ECU to a signal from a sensor. For example, a sine wave may be changed to a square wave.
Pulse Wheel: Toothed sensor wheel used to induce or affect electrical currents in magnetic inductive pulse generators, such as engine speed and position sensors.
Pulse Width: The operating phase of an actuator when it is energised by an electronic control unit.
Pump: Device that is electrically or mechanically driven to pressurize a fluid or gas.
Purge Valve: The valve in a fuel vapour evaporative system operated from the ECM under specific conditions to draw air back through the evaporative canister. An emission control device to prevent hydrocarbon fuel vapours from the fuel tank escaping into the atmosphere. :
Push Fit: The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is the same as the outer dimension of the inner component. Also known as a transition fit.
Push Rod: A rod that transfers movement from a cam follower to a rocker arm.
Pyrotechnic: Explosive devices!
Pyrotechnic Inflater: An explosive device used to produce a large quantity of gas to inflate an air bag.