Impala SS Dictionary

This page comes at the request of many new members who have troubles with the abbreviations, part names, etc. that are used in the FAQ, mailing list, and other locations. In it you will find a hodge-podge of sensor terms, acronyms, slang, and other stuff that I hope will be useful. If you have a term which you feel should be included, let me know and I'll get it in as soon as possible. Thanks.

• 1LE
  Special code used on Chevrolet Camaros to indicate that they are equipped with the racing performance package. This package deletes air conditioning and several other luxury items and beefs up the suspension. The 1LE intake elbow is useful for Impala engine modifications

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• 6J6
  The 6J6 option is two 4" diameter red lights (one left side, one right side) that face rearward and are mounted inside the car behind the rear seats and above the rear package shelf (under the rear window). These come on when you use the brakes or use the turn signals. They are an option on the 9C1. See also: 9C1.

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• 9C1
  Chevrolet order code for the police package option on the Caprice. This is usually used to refer to parts that only come as part of this package, such as "9C1 Trunk Mat".

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• ABS
  Acronym for Antilock Braking System. This system prevents the tires from "locking up" under heavy braking or slick conditions by modulating pressure to the brakes when sensor determine that the tire is no long rolling. This allow quicker, straighter stops in most conditions than standard braking.

• AIR
  Abbreviation for the Secondary Air Injection System. This sytem helps reduce emissions and heats up the catalytic converters more quickly after startup so exhaust gas conversion can occur sooner. See also: Air Pump.

• Air Box
  The enclosure that houses the air filter. Air comes into the "box" from a small rectangular opening on the front, and is then fed through the air filter to the top of the box. See also: First Base.

• Air Pump
  The AIR pump pressurized air from the air cleaner and pumps it back into the check valves near the exhaust manifolds. This is the key part of the AIR system. The AIR pump is electric and presents no drag on the engine. See also: AIR.

• ALDL
  Acronym for assembly line diagnostic link. This is the small black connector underneath the driver's dash. This connector allows the dealer to plug in scan tools to test and report the status of the PCM. This is how the dealer scans for trouble codes. This is also how the PCM can be reprogrammed. See also: PCM, HPP.

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• Baffle
  Another name for the resonators that are on used to quiet the Impala's air intake. See also: Pitchers Mound, Home Plate, Resonator.

• BBB
  Acronym used by owners of black Impalas who feel left out because they don't have a cool acronym like DCM or DGGM to use. Actually, the official GM name is Standard Onyx Black, but that isn't used for obvious reasons. Usually taken to mean Bad to the Bone Black. See also: DCM, DGGM.

• BBT
  Acronym for Blue Bow Tie. This is a part from the 97 Cavalier that will drop into the same place the silver bow tie on the front of the Impala grill is from the factory. It seems to look better on the DGGM Impalas than the red bow tie. See also: RBT, CRBT, DGGM.

• BTSI
  Acronym for Brake Transmission Shift Interlock. This is a solenoid that prevents you from shifting out of park unless your foot is pressing on the brake pedal. This is touted as a safety feature, but is commonly thought to be a direct result of the lawsuits filed by some Audi owners claiming "unintended acceleration" of their cars when they were started.

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• Catalytic Converter
  Module attached to the exhaust manifold that, when heated, can convert the harmful emissions of the engine to relatively harmless gasses. It contains very rare and expensive metals for this process. See also: Export Pipes.

• CHMSL
  Acronym for Center High Mounted Stop Lamp, which is the third brake light located at the bottom of the rear window.

• Clear Flood Mode
  A special starting mode that allows for clearing of excess fuel in the engine. It is made to emulate the method for clearing floods in carburated cars. The throttle must be depressed to 80% or more. The PCM will then lean the air/fuel mixture out to 20:1 to clear the flood. Clear flood mode is automatically shut off when engine RPM is greater than 300 RPM.

• Closed Loop Mode
  A run mode of the engine when it has warmed up and is using mainly the oxygen sensor for very accurate monitoring and control of the air fuel ratio. In this mode, the engine is running very close to stoichometric (14.7:1). See also: Stoichometric, Oxygen Sensor.

• Cold Air Induction
  A general classification of mechanisms designed to get cooler air from outside the engine compartment into the engine intake tract. This is usually accomplished by some sort of scoop or ducting to the outside.

• CRBT
  Acronym for Cavalier Red Bow Tie. This bow-tie is a drop-in replacement for the bow-tie on the grill of the stock Impala. See also: BBT, RBT.

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• Data Link Connector
  A 16 pin connector located underneath the instrument panel on the drivers side. This connector is used to verify correct engine operation before the engine leaves the assembly plant and also by technicians to retrieve DTC's stored inside the PCM. This connector can also be used to flash the PCM with a new program. See also: Flash, DTC, PCM.

• DCM
  Acronym for Dark Cherry Metallic, one of the available colors for the Impala in 1995 and 1996. See also: GGM.

• DGGM
  Acronym for Dark Green Grey Metallic, one of the available colors for the Impala in 1995 and 1996. See also: BBB, GGM, DCM.

• Diagnostic Trouble Code
  A special code stored inside the PCM when a malfunction is indicated. These codes may be retrieved and examined using some type of scan tool connected to the DLC. To clear touble codes, the battery must be disconnected from the PCM. A DTC does not mean that the engine should be stopped immediately, but that the cause of the DTC should be checked as soon as possible. See also: Scan Tool, DLC, PCM.

• DLC
  Acronym for Data Link Connector. See also: Data Link Connector.

• DRL
  Acronym for Daytime Running Lights. This GM option turns the headlights on at a reduced voltage during all operating conditions. During nighttime operation, the headlights are brightened and the rest of the running lights and the tail lights are also turned on. This option is required in Canada, but can be fitted to US models. This option is technically not compatible with the Twilight Sentinel, but you do get the basic twilight sentinal functionality. The front lamps just don't go off during daylight hours. On pre-1996 cars, the light sensor was not included with the package, so the tail lights had to be turned on manually at dusk. See also: Twilight Sentinel.

• DTC
  Acronym for Diagnostic Trouble Code. See also: Diagnostic Trouble Code.

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• ECT
  Acronym for Engine Coolant Temperature. This sensor is mounted in the coolant pump and sends engine temperature information to the PCM. The sensor is a thermistor that changes internal resistance as the temperature changes. When the resistance is high, the PCM interprets that the engine is cold. When resistance is low, the voltage through the wire will decrease and the PCM will interpret it as a warm engine. The ECT is located on the front of the engine, just below the water pump. See also: PCM.

• EEPROM
  Acronym for Electronically Erasable Programmable Read Only Memory. This is more commonly referred to as flash memory. This type of memory is to store the engine control parameters in the PCM. The EEPROM in the PCM can be reprogrammed using the Tech-1 scan tool. See also: Scan Tool, Tech 1, flash, PCM.

• EGR
  Acronym for Exhaust Gas Recirculation. This sytem reduces emissions, specifically Nitrogen Oxides caused by high combustion temperatures and excessive oxygen. It does this by decreasing combusion temperatures and displacing oxygen with spent exhaust gases. The main element is the EGR valve mounted on the intake manifold and operated by vacuum.

• EVAP
  Abbreviation for the Evaporative Emmisions Control System. This system utilized a charcoal canister to hold vapors from the fuel tank while the vehicle is not operating. When the engine is running, the vapor is purged from the canister into the normal intake path and consumed in the normal combustion process.

• Export Pipes
  Pipes that can be used in place of the catalytic converters for export use or off-road use only. These are used where there is no unleaded fuel available, since leaded fuel would ruin the catalytic converters See also: Catalytic Converter.

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• First Base
  First base is a common slang term for the rectangular, black resonator that is placed between the MAF and the intake elbow. This resonator rests on top of the radiator. It is called first base because of its close relationship to the Home Plate resonator on top of the engine. See also: Home Plate, Resonator, MAF.

• Flash
  Flash memory is a non-volatile form of read-only memory that is used in the Impala to store the computer program that controls the engine. It is located in the PCM. On earlier cars, this is known as "the chip" and is commonly replaced with a higher performance program stored on a different chip. On LT1 engines, the flash memory is reprogrammed through the DLC, which is often referred to as "flashing" the PCM. See also: DLC, PCM.

• Fuel Trim
  This is often the part of the PCM that is referred to as the "learning" section. There are two parts of fuel trim: short term and long term. Short term fuel trim is set using the oxygen sensor inputs to detect a lean or rich condition. The fuel trim is increase for a lean mixture decreased for a rich mixture. Over a period of time, if the mixture is continously rich or lean, this is learned into the long term trim, and the short term is returned closer to a more ideal position. Short term trim is frozen at the ideal value during power enrichment to remove the rich condition that results there from long term memory. See also: Power Enrichment, Oxygen Sensor.

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• GGM
  Acronym for Green Grey Metallic, one of the available colors for the Impala in 1995 and 1996. More commonly referred to as DGGM, for Dark Green Grey Metallic, but GGM puts it into the TLA (Three Letter Acronym) territory. See also: BBB, DGGM, DCM.

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• HO2S
  Acronym for Heated Oxygen Sensor. The LT1 uses heated oxygen sensors to determine if the engine is running lean or rich. See also: Oxygen Sensor.

• Home Plate
  A slang term invented for the triangular resonator that sits on top of the engine to reduce the noise level of the intake air path. It is so named for its resemblance to a common home plate shape in baseball. See also: Pitchers Mound, Resonator.

• HPP
  Acronym for the Hypertech Power Programmer. This device reprograms your PCM with a custom performance program. You insert it through the ALDL underneath you dash. It then reads the stock program out, modifies it according to your parameters, and stores it back. You can reprogram and deprogram your PCM at will. See also: ALDL, PCM, HPP+, HPPP.

• HPP+
  Another name for the Hypertech Power Programmer Plus. See also: HPPP.

• HPPP
  Acronym for the Hypertech Power Programmer Plus. This device works much the same way as the HPP, but allows more parameters to be modified, and will eventually allow custom cartridges to be inserted to function as scan tools and other functions. This is the second generation of the HPP. See also: ALDL, PCM, HPP+, HPP.

• HVAC
  Acronym for the Heating, Ventilation, and Air Conditioning system

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• IAC
  Acronym for the Idle Air Control valve. See also: Idle Air Control.

• IAT
  Acronym for Incoming Air Temperature. This sensor is mounted in the elbow that connects to the throttle body and monitored by the PCM. The PCM controls fuel delivery and spark timing based upon the incoming air density. See also: PCM.

• Idle Air Control
  The purpose of the Idle Air Control valve is to control engine idle speed to prevent stalls based upon changes in engine load. The IAC control is mounted in the throttle body and can bypass air around it based upon PCM control.

• IMHO
  Acronym for In My Humble Opinion. Used in internet e-mail correspondence to distinguish fact from opinion.

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• JATO
  Acronym for Jet Assisted Take Off. The military uses JATO rockets to assist in getting heavy planes off of the ground. There is an urban legend about someone who strapped one to their Impala out in the desert and then crashed into a cliff doing around 300MPH. The story is a complete fabrication, and ends up being posted to the Impala mailing list about once a month.

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• Knock Sensor
  Two sensors are mounted in the block to detect knock or detonation in the engine. If it is detected, the PCM retards the spark to prevent damage to the engine. This allows for variations in octane levels without damaging the engine. Often referred to by the acronym KS. There is also a module inside the PCM that is used to monitor for knock from the sensors. See also: KS.

• KS
  Acronym for the Knock Sensor. See also: Knock Sensor.

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• MAF
  Acronym for the Mass Airflow Sensor. The MAF sensor used on the Impala is the hot-wire type. The output frequency from the MAF is a function of the power required to keep the air flow sensing elements (hot wire) at a fixed temperature above ambient. As air flow increases, a greater amount of current is required to keep the wires at a constant temperature due to the cooling affect of the increased quantities of air. The MAF is directional and must be installed in the proper direction.

• Malfunction Indicator Lamp
  This is the infamous "Service Engine Soon" light. It indicates to the driver that a problem has occured and that the vehicle should be taken in for service as soon as possible. The light will go off when the engine is restarted unless there is a failure in the self-diagnostics of the MIL system. In any case, a trouble code (DTC) is stored for later retrieval via a scan tool. A lit MIL does not mean that the engine should be stopped immediately: rather, the cause of the MIL should should be checked as soon as possible. See also: SES, DTC, MIL.

• MAP
  Acronym for Manifold Absolute Pressure. This sensor measures the change in the intake manifold pressure as speed and engine load changes. As the manifold pressure increases, the air density in the intake manifold also increases.

• MIL
  Acronym for Malfunction Indicator Lamp. See also: Malfunction Indicator Lamp.

• Mobil 1 Cap
  Special oil filler cap that was supplied on Corvettes equipped with Mobil 1 from the factory. States to use "Mobil 1 Oil Only". Will fit Impalas with the 'Vette valve covers or stock '94 Impalas. See also: Mobil 1 Plate.

• Mobil 1 Plate
  Special notification plate that was supplied on Corvettes equipped with Mobil 1 from the factory. States to use "Mobil 1 Oil Only". A nice addition for those Impalas using Mobil 1 oil. See also: Mobil 1 Cap.

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• NAISSO
  Acronym for National Association of Impala SS Owners, a nationwide organization of over 500 Impala SS Owners. Troy Wilrick runs it from Florida, and there are many regional chapters springing up all over. See my home page for more details.

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• O2 Sensor
  Abbreviation for Heated Oxygen Sensors. See also: Oxygen Sensor.

• OBD-II
  Acronym for On-Board Diagnostics II, a system instituted by a Federal standards committee that forces the engine control system to be able to monitor for a failure in any sensor in the emmisions control circuitry. This is only fully implemented on 1996 Impalas. This required PCM changes and an extra set of oxygen sensors to be fitted to 1996 Impalas.

• Open Loop Mode
  A run mode of the engine when it is first started. In this mode, the PCM ignores the oxygen sensors and calculates the air/fuel ratio based upon inputs from the MAF, ECT, and TP sensors. The system stays in this mode until the O2 sensors have varying values, the coolant temperature has raised to a preset value, and a preset amount of time has expired. See also: Oxygen Sensor, TP, ECT, MAF.

• OptiSpark
  The distributor ignition system on the LT1 engine. This system utilizes an optical sensor to detect timinng pulses on the crankshaft. The PCM then receives both a low resolution (4x) and high resolution (360x) signal to control timing to the injectors.

• Oxygen Sensor
  The LT1 in the Impala engine contains two heated oxygen sensors near the catalytic converters. These oxygen sensor provide feedback to the PCM that tells it if the engine is running rich or lean. A voltage of 450mV from the oxygen sensor indicates that the engine is running perfectly (stoichometric), which means that all of the air and all of the fuel are being used during the combustion process. If the value is lower than 450mV, the engine is running lean, which means that there was too much oxygen in the combustion process. If it is greater than 450mV, the engine is running rich. The PCM adjusts in both the short and long term for the effects of the oxygen sensors. The O2 sensors do not work until they have reached about 600 degress F. Until then, they look like an open circuit to the engine, and the PCM must "guess" what mixture to use. Also, the O2 sensors are ignored by the PCM during wide-open throttle time periods. See also: WOT, PCM.

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• PASS-Key
  Acronym for Personalized Automotive Security System. General Motors designed anti-theft system. It operates by using a specific resistor in the ignition key. A signal is sent to the PCM only if the corect resistor is detected that will enable the starter circuit and the injectors. The car will not run even if the crank circuit is bypassed (hot-wired). A DTC is stored if the wrong resistor is sensed by the PCM. See also: DTC, PCM.

• PCM
  Acronym for Powertrain Control Module See also: Powertrain Control Module.

• PCS
  Acronym for Pressure Control Solenoid. This solenoid allows the PCM to vary the line pressure to the transmission to make shifts crisper and harder based upon throttle position, engine RPM, etc. This feature allows for aftermarket PCM programs to incorporate an electronic "shift kit" without opening up the transmission.

• PDP
  Acronym for Purple Door Panels. Some Impala door panels come from the factory with a purple tint to them. They tend to very: some may have a definite purple color, others may be slightly tinted. We are in the process of trying to get GM to issue an official TSB on this issue, otherwise, you can take your chances on getting your local dealer to replace them for you. See also: TSB.

• Pitchers Mound
  A slang term invented for the rectangular resonator that connects the air cleaner box to the MAF sensor. Its purpose is to reduce the noise level of the intake air path. It is so named because of its relationship with Home Plate and its rectangular shape. See also: Home Plate, Resonator, MAF.

• Power Enrichment
  A condition entered into by the PCM during wide open throttle (WOT). During this time, the PCM gives the engine extra fuel for more power. Short term fuel trim is not used during this mode, nor are the oxygen sensors, since the mixture is inherently rich. See also: Fuel Trim, Oxygen Sensor, WOT.

• Powertrain Control Module
  The heart of the control system on the LT1 engine. It monitors sensors to retrieve information about engine operation and the various systems that it controls. It also has the ability to do diagnosis on itself and other parts of the system, and light the MIL and store a DTC if it senses a problem. See also: DTC, MIL.

• PSP
  Acronym for Power Steering Pressure switch. When the power steering pressure is high, the PCM is alerted so that it can raise idle speed to prevent the engine from stalling under the increased load.

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• RAM
  Acronym for Random Access Memory. This is the PCM's scratch pad. The processor can read or write from this memory as needed. This memory is erasable and requires battery power to be retained. If the battery is disconnected, this memory is lost. The DTC's are stored in RAM. See also: DTC, EEPROM, flash, ROM.

• RBT
  Acronym for Red Bow Tie. The red bow-tie has become the unofficial symbol of NAISSO. It involves replacing or taping over the OEM chrome bow-tie on the grill of the Impala. There is a nice unit from the Cavailier that does it nicely. This is the only part of Jon Moss's concept car that didn't make it into production. See also: BBT, CRBT.

• RCDLR
  Acronym for Remote Control Door Lock Receiver, the unit mounted in the trunk that receives the remote locking keychain signals and sends the signals to lock or unlock the doors

• Resonator
  A baffle meant to reduce noise in an air passageway. There are several baffles on the Impala. The first is a black rectangular piece after the air clean but before the MAF. The second is the triangular black plastic piece that sits on top of the engine. These two resonators serve to reduce air noise entering the engine. There are also two exhaust resonators just before the tips at the rear of the car. These serve to reduce exhaust noise. See also: Pitchers Mound, Home Plate.

• ROM
  Acronym for Read-Only Memory. There is permanent memory physically soldered into the boards within the PCM. The ROM contains the overall control programs. Once the ROM is programmed at the factory, it cannot be changed. It is non-erasable, and does not require battery power to be retained. See also: RAM, EEPROM, flash.

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• Scan Tool
  A hand-held electronic tool used to analuze and diagnose control module systems. It can be used to read DTC's stored in the PCM, monitor sensor data in real time, or flash the PCM with a new program. The primary tool used GM technicians is the Tech 1. Other aftermarket tools are also available, such as JET's Auto X-Ray and the Diacom monitor. These tools are useful for tuning and for diagnosing faults. See also: Tech 1, PCM, DTC.

• SES
  Acronym for Service Engine Soon, which is what is commonly displayed on the Malfunction Indicator Lamp indicator. The lamp is now more properly referred to as the Malfunction Indicator Lamp, or MIL. See also: Malfunction Indicator Lamp, MIL.

• Sewer Pipe
  Slang for the common practice of using PVC tubing from the plumbing section of your local home goods store to replace the first base resonator. Two elbows make an almost exact fit between the stock instake elbow and the air box. See also: First Base.

• SFI
  Acronym for Sequential Multiport Fuel Injection

• Shower Drain
  Slang for the mesh piece of metal inside of the export exhaust pipes. It resembles a shower drain cover, and is probably in place to quiet the exhaust as it passes through the straight pipes. Most commonly removed. See also: Export Pipes.

• SIR
  Acronym for Supplemental Inflatable Restraint, which is the technical term for GM's version of the air bag.

• SPE
  Acronym for Sewer Pipe Equipped, which refers the the homemade PVC pipe intakes installed on some cars.

• Speed Density
  A mode of operation where the engine determines the fuel needs from engine speed and air density. The air density is computed from the IAT and MAP sensors. These inputs allow the PCM to compute the amount of fuel it needs to deliver via the injectors. This method is less accurate than reading the MAF sensor and is only used if there is a fault in the MAF circuit. On OBD-II cars, this method is used to check the MAF for errors. This method requires changes to the PCM to compensate for modifications to the engine. See also: MAF, MAP, IAT.

• SS
  Super Sport, a moniker commonly given to some of Chevrolets high performance cars. See also: Z28.

• Stoichometric
  A chemical term used when both elements in a process are completely used in a reaction. In this case, it refers to the oxygen and the fuel being burnt in the engine. This air/fuel ratio is usually 14.7:1. See also: Closed Loop Mode, Oxygen Sensor.

• SWC
  Acronym for Steering Wheel Controls, which allows you to adjust radio parameters from buttons placed on the steering wheel.

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• T84
  The bulbs used in the export headlights that produce a generally brighter and sharper beam than the standard.

• TCC
  Acronym for Torque Converter Clutch. The torque converter allosw limited slippage inside of the transmission to allow the engine to spool up into its power band quicker, and to allow the engine to idle while still in gear. The TCC "locks up" via this clutch while at highway speeds to reduce parasitic losses through the slippage. Lockup is controlled via the PCM.

• Tech 1
  A hand-held scan tool most commonly used by GM technicians. They cost upwards of $1000 each, but are very complete in their coverage of the LT1 engine parameters and have the capability to flash the PCM with a new program. See also: PCM, Scan Tool.

• TFT
  Acronym for Transmission Fluid Temperature. A sensor input used by the PCM for unknown purposes, probably to control shift feel.

• Throttle Body
  The throttle body is located on the front of the engine attached to the intake manifold. Its job is to control air flow to the engine based on the throttle position, which controls the speed of the engine. During idle, the throttle body is almost closed and idle speed is controlled by the IAC valve. See also: PCM, IAC.

• Throttle Position Sensor
  Provides a voltage to the PCM that changes in relationship to the throttle blade opening or closing. This signal varies from about .6 volts as idle to about 5 volts at WOT. The TPS is one of the most important sensors used by the PCM for fuel control and most of the other PCM controlled outputs. See also: WOT.

• TPS
  Acronym for Throttle Position Sensor. See also: Throttle Position Sensor.

• TS
  Acronym for Twilight Sentinel. See also: Twilight Sentinel.

• TSB
  Acronym for Technical Service Bulletin. These are short papers distributed to GM technician to help them diagnose and remedy common complaints and problems. They are not the same as recalls, which are done at no cost to the consumer and are usually only performed for safety reasons. TSBs are usually covered under the original warranty, if it is still in effect.

• Twilight Sentinel.
  The twilight sentinel uses a sensor near the defogger vent to detect whether it is light or dark outside. If it is dark, it automatically turns the headlights on. Similarly, if it is light, it turns them off. It also has a feature that leaves the lights on for a specified period of time after the car is shut off as a security measure. This option is incompatible with DRLs. See also: DRL.

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• UEC
  Acronym for Underhood Electrical Center. This is a black box that is located near the firewall on the passengers side. Inside the box you will find various fuses and relays, and beside it you will find the auxiliary battery terminal.

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• Vehicle Speed Sensor
  A permanent magnet generator located in the transmission. It transmits a pulsing AC voltage in relation to the speed of the vehicle. The PCM converts the pulsing frequency to a speed and sends it to the speedometer, odometer, cruise control, chime module, and power steering control module. See also: PCM.

• VSS
  Acronym for the Vehicle Speed Sensor See also: Vehicle Speed Sensor.

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• WOT
  Acronym for Wide Open Throttle. This occurs when the throttle is opened more than about 75%. See also: Power Enrichment.

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• Z28
  Option code for the Camaro high performance package. Many of the parts from the current generation of the Camaro Z28 will fit Impalas. See also: 1LE, SS.

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