Glossary
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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
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 sqrd 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
CAN - Controller Area Network; a serial data network used to transfer control data between
various ECUs of an automotive system & defined by SAE J2284, also referred to as VDB
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
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
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
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
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
EGS - Electronic Getriebe System; an ECU which controls the transmission
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
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
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 RS232 interface protocol with level conversion,
0/+12 volts to +/-12 volts for RS232
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 RS232 interface protocol with level conversion,
0/+12 volts to +/-12 volts for RS232
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
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
PROM - Programmable Read Only Memory; a semiconductor memory device which can be
electrically programmed externally
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
VAF - Volume Air Flow; the quantity of air flow in cubic meters per second measured by an AFM
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
WBLS - Wide Band Lambda Sensor; an O2 sensor which provides a linear output for Lambda
from .7 to 2.4 used for more precise emissions control
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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