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   Automotive Electronics Terms/Acronyms

    AAR - Auxiliary Air Regulator; a valve which controls idle air and affected by a heater element

    AAV - Auxiliary Air Valve; a valve which controls idle air and affected by water temperature,
                or a valve which momentarily increases the idle during startup and actuated by vacuum

    ABD - Automatic Brake Differential; an electronic control system for traction control which prevents
                loss of wheel traction by applying wheel braking to non limited slip differentials

    ABS - Anti-Lock Braking; an electronic control system which prevents wheel lockup, reducing the
               loss of wheel traction and thus enhancing skid avoidance

    ADC - Analog to Digital Converter; a semiconductor device which samples an analog signal and
                converts it to a binary number that represents the analog value, i.e. all engine parameters
                (e.g. temperature) are analog values which must be converted for processing by the MCU

    AFI - Adaptive Fuel Injection; a fuel injection system which can adapt to engine changes over
              time and control emissions, e.g. intake air leaks, fuel pressure changes & engine wear

    AFM - Air Flow Meter; a device used to sense intake air volume flow (VAF) for a fuel injection
                system, but does not compensate as well for air density as does a AMS/MAFS,
                where output = F (density X velocity ^ 2 X area of sensor intake) or,
                where V(out) for digital ECM = K X (angular position of flap, 0-110 degrees) or,
                where V(out) for analog ECM = K X (sqrt angular position of flap, 0-110 degrees) or,
                where V(out) for analog ECM = K X V (air volume - cubic meters/sec) = VAF or,
                where MAF = density X VAF

    AFR - Air Fuel Ratio; the ratio of intake air to intake fuel, ideally 14.7 for emissions control
               and 12.6 for maximum torque, AFR = 14.7 X (CO2 - CO) / (CO2 - O2 / 2)

    AGS - Automatic Transmission Controller; an ECU which controls the transmission

    AMS - Air Mass Sensor; a device used to sense the quantity of the intake air mass for a fuel
                injection system, which results in a more precise fuel injection control than an AFM,
                where output = density X velocity X area of sensor intake, e.g. MAFS

    ASR - Acceleration Slip Reduction; an electronic control system usually integrated in the ABS
               system which reduces wheel slip, e.g. snow, ice, & mud, during acceleration by applying
               wheel braking to the slipping wheel

    BAS - Brake Assist System; an electronic control system which prevents wheel lockup, reducing the
               loss of wheel traction and thus enhancing skid avoidance, e.g. ABS

    BFI - Bank Fuel Injection; a fuel injection system where all cylinder injectors operate at once

    BTDC - Before Top Dead Center; a timing position before the upper most piston position
                  on the crank cycle

    CAFE - Corporate Average Fuel Economy; a U.S. federal regulation which defines the required
                  average fuel economy of an automobile manufacturer

    CAN - Controller Area Network; a serial data network used to transfer control data between
                various ECUs of an automotive system & defined by SAE J2284 & ISO 11898,
                also referred to as VDB, similar electrically (physical layer) to RS-485

    CARB - California Air Resources Board; an agency which sets air quality standards & provides
                  guidelines to be defined by the SAE for automotive emissions controls compliance

    CAT - Catalytic Converter; a device used to reduce emissions with Lambda controlled to 1.0

    CCU - Climate Control Unit; the main element of a climate control system which controls all
                other elements, e.g. valves, mixing flaps & solenoids

    CDI - Capacitive Discharge Ignition; an ignition system where energy is stored in capacitor
               and transferred to an ignition coil to develop an ignition spark

    CEL - Check Engine Light; an instrument panel light used to indicate an engine fault which
               can be read by a diagnostic tester, also called a MIL

    CHT - Cylinder Head Temperature; a NTC sensor which is used to determine the
                cylinder head temperature, e.g. TS, ECT

    CIS - Continuous Injection System; a fuel injection system where fuel is provided to each
              independent cylinder continuously at a varying pressure based on intake air flow and
              engine load, either electrically or electronically controlled for performance

    CKP - Crankshaft Position and Speed Sensor(s); a sensor or sensors which is (are) used to
                provide a crankshaft position reference and a speed signal(s)

    CMP - Cam Position Sensor; a sensor used to determine TDC for SFI and/or DIS systems

    CO - Carbon Monoxide; a toxic gas which results from an incomplete combustion process,
              the lack of adequate oxygen, i.e. a low AFR

    COP - Coil-On-Plug; an ignition system where each cylinder has a unique ignition coil,
               also referred to as Direct Ignition System (DIS)

    CO2 - Carbon Dioxide; a non-toxic gas which results from a complete combustion process

    CSV - Cold Start Valve; a valve used on early fuel injection systems to provide fuel enrichment
                for cold starts, i.e. controlled by the starter solenoid (+) and the thermal time switch (-)

    Cycle - OBDII Self Test; a test of the basic functioning of the emissions control system which
                 includes; TWC efficiency, O2 sensor aging, SAI diagnosis, fuel tank venting, and
                 TRA & FRA range diagnosis

    D-Bus - Diagnostics Bus; a bidirectional bus used to access DTCs, pin 7 of OBDII connector

    DI - Direct Injection; a fuel injection system where fuel is injected directly into the cylinder
            versus into the intake manifold

    DIS - Direct Ignition System; an ignition system where each cylinder has a unique ignition coil,
               also referred to as Coil-On-Plug (COP)

    DLC - Diagnostic Link Connector; a standardized connector defined by OBDII (J1962) for
               DTC access; pin 4 - chassis grd, pin 5 - signal grd, pin 7 - K Line (ISO 9141), ,
               pin 16 - +12V, pin 6 - CAN high, pin 14 - CAN low, pin 15 - L line (ISO 9141),
               pins 2 & 10 (J1850), pins 1, 3, 8, 9, 11, 12, 13 vehicle specific

    DM - Diagnostic Module; an ECU which provides engine monitoring & diagnostics for the
               distributed engine management system (multiple ECUs for fuel, ignition, & throttle)
               used by Mercedes Benz vehicles prior to that functionality being integrated into a single
               ECM. OBDI necessitated this ECU (N59) for 1992 vehicles. On ODBII vehicles,
               the DM (N59/1) communicates with other ECUs resulting in additional ECU access
               via the DLC. Later vehicles utilized the OBDII CAN pins 6/14 for direct ECU access

    DME - Digital Motor Electronics; an ECM which integrates both a fuel injection system and
                a ignition system and named by Bosch/Porsche/BMW, e.g. Porsche DME,
                BMW DME, also called Motronic

    DSC - Dynamic Stability Control; an electronic control system which reduces lateral acceleration
               which may result in a loss of wheel traction causing the vehicle to spin by reducing engine
               torque and thru controlled wheel braking

    DSP - Digital Signal Processing; a method of analyzing an analog signal by converting it into
               a digital form and then further converting it from the time domain to the frequency domain

    DTC - Diagnostic Trouble Code; a fault code provided by the diagnostic section of an ECU,
                may include a description of the fault in addition to a numeric code

    ECM - Engine Control Module; the main element of any automotive engine management system,
                e.g. fuel injection/ignition control unit, Motronic unit, or DME unit

    ECT - Engine Coolant Temperature Sensor; a NTC sensor which is used to determine the
               cylinder head temperature, e.g. CHT, TS

    ECU - Electronic Control Unit; a functional element of an automotive electronic system,
                e.g. ECM, fuel injection unit, transmission control unit, CCU or cruise control unit

    EEPROM - Electrically Erasable & Programmable Read Only Memory; a semiconductor
                       memory device which can be electrically programmed and erased externally,
                       also referred to as flash memory or flash EPROM

    EFI - Electronic Fuel Injection; a fuel injection system where fuel is injected at a constant
              pressure but with varying injector opening times based on numerous variables,
              e.g. engine temperature, RPMs & load

    EGR - Exhaust Gas Recirculation; the feedback of the exhaust gas to the intake to reduce NOx,
              whereby the combustion chamber temperatures are reduces. The conditions for a typical
              EGR system to operate are; a light engine load, an intermediate engine RPM, and an
              engine at normal operating temperature

    EGS - Electronic Getriebe System; an ECU which controls the transmission

    Egas - Electronic Throttle Actuation; a Porsche ECM with an electronically controlled throttle body

    EHA - Electric Hydraulic Actuator; a device to control the fuel pressure on a electronic CIS
               fuel injection system for cold running & emissions

    EML - Electronic Motorized Luft; electronic actuated throttle control system, e.g. drive-by-wire

    EPA - Environmental Protection Agency; a U.S. Government agency which sets environmental
               standards

    EPROM - Erasable Programmable Read Only Memory; a semiconductor memory device
                     which can be electrically programmed externally and erased using a UV light

    EVAP - Evaporative Emission System; an emission system which controls fuel evaporations into
                  the air

    EWS - Electronic Immobilization System; an anti-theft system that has an electronic ignition key
                coded to the vehicle, which inhibits the ECM from functioning

    EZK - Electronic Ignition with Knock Control; an ignition system which utilizes knock sensors
               to prevent engine knock the result of fuel grades, engine temperatures, & engine loads

    FFT - Fast Fourier Transform; a digital signal processing algorithm which can be used in
               an automotive knock control system whereby an actual analog time domain knock signal
               is converted into frequency domain signals to be compared to a characteristic frequency
               domain composite of the typical knock signal

    FRA - Fractional Relative Adaptation; a fuel injection adaptation method used to compensate
               for engine/sensor changes under load which affect the AFR, e.g. MAFS output error,
               with some ECMs retaining the old FRA values with battery removal & not updating until
               closed loop operation returns via the O2 sensors

    FV - Frequency Valve; a valve used to vary the CIS control pressure for emissions control

    Hall - Hall-Effect Device; a semiconductor device whose conductivity is affected by a magnetic
              field, either as a two wire sensor (switch) or as a three wire sensor (powered module)

    HC - Hydrocarbons; particulates of unburned fuel, the result of an inadequate AFR

    HFM - Hot-Film Mass Air Flow Sensor; a mass air flow sensor whose output voltage is based
                on a temperature differential across a heated resistive film network, a type of AMS

    IAC - Idle Air Control; an air valve controlled electronically used to maintain a constant engine
              idle, e.g. ISV

    IAT - Intake Air Temperature; a NTC sensor which is used to determine intake air temperature
              for the AFM or AMS

    IDI - Inductive Discharge Ignition; an ignition system where the spark energy is stored in the
             ignition coil

    IKE - Integrated Cluster Electronics; an instrument cluster which contains vehicle info, e.g. VIN

    ISO - International Standards Organization; an organization which defines product specifications
              to maintain a universal standard, e.g. ISO 9141 which defines an ECM interface protocol

    K Line - Data Port; a bidirectional serial communications port used to access ECU data
                  as defined by ISO 9141 using RS-232 interface protocol with level conversion,
                  0/+12 volts to +/-12 volts for RS-232

    KCS - Knock Control System; an adaptive feedback ignition system used to prevent detonation
               while optimizing the ignition advance to achieve maximum torque. One approach uses
               digital signal processing (DSP) where an analog knock signal in the time domain is
               converted into a digital form and analyzed, using one of the Fourier Transforms (FT),
               in the frequency domain.

    KS - Knock Sensor; a sensor which provides an indication of a too advanced ignition timing

    L Line - Command Port; a unidirectional serial communications port used to access ECU data
                 as defined by ISO 9141 using RS-232 interface protocol with level conversion,
                 0/+12 volts to +/-12 volts for RS-232

    Lambda - the ratio of the actual AFR to the ideal AFR of 14.7 & derived from an O2 sensor

    LH - Hot-Wire Mass Air Flow Sensor; a mass air flow sensor whose output voltage is based on
             a temperature differential across a heated wire in a resistive bridge network, a type of AMS

    MAFS - Mass Air Flow Sensor; a sensor used to measure the quantity of intake air mass
                  either by hot wire or hot film technology, e.g. AMS

    MAP - Manifold Absolute Pressure; intake manifold pressure used to determine engine load

    MCU - Microprocessor Control Unit; the main section of an ECM which contains the digital
                 processing elements, i.e. the microprocessor, the ADCs, and the memory devices

    MFI - Mechanical Fuel Injection; a fuel system where a mechanically controlled fuel distributor
               injects fuel into each independent cylinder based on engine RPMs and throttle position

    MIL - Malfunction Indicator Light; an instrument panel light used to indicate an engine fault
               which can be read by a diagnostic tester, also called a CEL

    Motronic - Bosch ECM; an ECM which integrates the ignition and fuel injection functions,
                     e.g. BMW Motronic, Porsche Motronic, also called DME

    MPFI - Multi-Point Fuel Injection; a fuel injection system which injects fuel to each independent
                 cylinder, e.g. BFI or SFI

    NOx - Oxides of Nitrogen; particulates of nitrogen which result from excess combustion heat
                (T > 2300 degrees F) & oxygen, e.g. excessive AFR, or a too advanced ignition timing,
                Air = N2 (78%) + O2 (21%), N2 + O2 > NOx

    NTC - Negative Temperature Coefficient; the typical characteristic used for temperature sensors,
                sensor resistance decreases with increasing temperatures, e.g. engine head/CCU sensors

    O2 Sensor - Oxygen Sensor; a sensor which provides an output used to determine Lambda,
                        more appropriately called a Lambda sensor, either narrow band (voltage range
                        of ~ .20 -.80 volts), or wideband (current range of ~ +/- 3-5 ma)

    OBDI - On-Board Diagnostics I; a 1988 regulation requiring a MIL, engine diagnostics,
                  non-standard diagnostic codes, non-standard diagnostic connector & electrical interface,
                  and volatile fault memory

    OBDII - On-Board Diagnostics II; a 1996 regulation requiring standardized diagnostic codes per
                  SAE J2012 and a standardized connector per SAE J1962, a non-volatile fault memory,
                  and a MIL, with emphasis on emissions & system failures complying with J1850 or
                  ISO 9141-2 protocol

    OEM - Original Equipment Manufacturer; a producer which manufactures the initial product

    P-Code - Trouble Code; a numeric fault code provided by the diagnostic section of an ECU,
                     generally related to the engine ECM, e.g. DTC

    PCM - Power Control Module; the main element of any automotive engine management system,
                also commonly called ECM

    PROM - Programmable Read Only Memory; a semiconductor memory device which can be
                   electrically programmed externally

    RS-232 - Serial Send/Receive Protocol; a serial communications protocol used to transmit and
                   receive data over a two wire connection where each element transmitted is a baud
                   which consists of a start bit, a stop bit, and typically 8 data bits. Usually a UART
                   type device is used to control the transmission process.

    SAE - Society of Automotive Engineers; an automotive standards setting group

    SAI - Secondary Air Injection; an exhaust air injection which is used at initial engine startup
              to reduce emissions before the TWC reaches the proper temperature to be effective

    SFI - Sequential Fuel Injection; a fuel injection system where each fuel injector provides fuel
              at a unique time for each cylinder

    SMD - Surface Mount Device; an electronic packaging technology which eliminates component
                mounting holes in printer circuit boards and reduces component lead lengths to small tabs

    TBI - Throttle Body Injection - a fuel injection system where fuel is injected at one central point

    TBS - Throttle Body Switch - a switch mounted on the throttle body to provide idle and WOT
               positions, also referred as TVS

    TCI - Transistor Controlled Ignition; an ignition system where a semiconductor device is used
              as a switch to control the current in an ignition coil, i.e. a type of IDI

    TDC - Top Dead Center; the upper most piston position on the crank cycle

    TPI - Tuned Port Injection; an early BFI fuel injection system used by GM, later systems were SFI

    TPS - Throttle Position Sensor; a device used to determine the position of the throttle butterfly
               by providing a variable voltage output as an indication of the angular throttle position, and
               can function as a proxy to determine engine load when calculated with the engine RPM

    TRA - Time Relative Adaptation; a fuel injection adaptation method used to compensate for engine/
               sensor changes at idle, which are short term & small affecting the AFR, e.g. intake air leaks,
               and which generally varies equally with +/- values under normal conditions

    TRIM - Fuel Injection Adaptation; a function provided by OBDII to correct the fuel injection pulse
                 width for AFR variations beyond the range of the O2 sensor, e.g. FRA (percent change) -
                 driving mode (open/closed loop), TRA (millisecond change) - idle mode (closed loop)

    TS - Temperature Sensor; a NTC sensor which is used to determine the cylinder head temperature;
             CHT, ECT

    TVS - Throttle Valve Switch - a switch mounted on the throttle body to provide idle and WOT
               positions, also referred as TBS

    TWC - Three Way CAT; a catalytic converter which reduces the emissions of CO, HC, & NOx

    UART - Universal Asynchronous Receiver Transmitter; a function used for serial communications
                between a processor, e.g. a scanner, and an external device, e.g. an automotive ECU via
                the K-line, using RS-232 protocol where an element of transmission is a baud

    VAF - Volume Air Flow; the quantity of air flow in cubic meters per second measured by an AFM

    ValveTronic - Variable Camshaft Timing & Lift; a continuously variable intake & exhaust
                camshaft timing system with variable valve lift used by BMW starting in 2001

    Vanos - Variable Camshaft Timing; a variable camshaft timing system used by BMW which can
                be just variable intake valve timing (starting in 1992) or both intake & exhaust valve timing
                and can be continuously variable on later engines, e.g. Mini Cooper S (R56) intake camshaft

    VarioCam - Variable Camshaft Timing; a variable intake camshaft timing system used first by
                Porsche in its 968 engines and later in its early 996 engines

    VarioCamPlus - Variable Camshaft Timing & Lift; a continuously variable intake & exhaust camshaft
                timing system with variable valve lift used by Porsche in engines subsequent to VarioCam

    VarioRam - Variable Intake System; a Porsche engine intake system used on 1996 and later 993
                engines that incorporates a second throttle body to further modify the intake system below the
                5200 RPM resonance intake system of the Porsche 964 engine to enhance low end torque

    VCA - VarioCam Actuator; a device used to change the camshaft timing to optimize engine torque

    VDB - Vehicle Data Buss; a serial data network used to transfer control data between various
                ECUs of an automotive system & defined by SAE J2284, also referred to as CAN

    VIN - Vehicle Identification Number; a number which is unique to each manufacturer's vehicle

    VSS - Vehicle Speed Sensor; a sensor which provides the vehicle speed input to the ECM & IKE

    VVT - Variable Valve Timing; variable camshaft timing which may include variable lift

    WBO2 - Wide Band Oxygen Sensor; an O2 sensor which provides a linear output current from
                   a negative .70 ma (rich) to a positive 2.4 ma (lean) with an AFR range from 9 to over 17

    WOT - Wide Open Throttle; the maximum open position of a throttle body

    WUR - Warm Up Regulator; a device used to control the fuel pressure on a CIS fuel injection
                 system and affected by engine temperature and a heater element

 



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