Glossary of Terms

Abbreviation / Topic Description
A/C Air Conditioning
Wikipedia: Air conditioning
ABS Anti-lock Braking System
Wikipedia: Anti-lock braking system
AC Alternating Current
Wikipedia: Alternating current
ACC Accessory
ADA Active Driving Assist {Japanese models only?}
ADM Australian Domestic Market
ASCII American Standard Code for Information Interchange
7-bit character set encoding, defines 128 characters.
Linux/Unix systems have a very useful man page installed: man ascii
Wikipedia: ASCII
ASS Auto Start Stop
dedicated control unit; there have been some firmware updates for it
Wikipedia: Start-stop system
AT Wikipedia: Automatic Transmission
ATF Automatic Transmission Fluid
Wikipedia: Automatic transmission fluid
AWD All Wheel Drive
BIU, BCU Body Integrated Unit, Body Control Unit
Electronic control unit handling chassis and miscellaneous comfort features mostly. E.g. door locking, lights, wipers, defogger, seat belts, power windows. Some items can be configured (coded) using tester software (SSM-III, SSM4): interior lighting, auto lock time etc.
In Subaru cars it connects high and low speed CAN busses, for example, transferring various engine and VDC/ABS (speed) data to dashboard unit.
CAN Controller Area Network is a vehicle bus standard.
Wikipedia: CAN bus
CC Cruise Control
Wikipedia: Cruise Control
CID, CALID Calibration Identification. ID for the software (ROM) installed on the ECU.
CVN Calibration Verification Number. Used to verify the integrity of the vehicle software; manufacturer specific; type of CVN depends on model; usually based on ROM checksums
Subaru Diesel models: 8 bytes (16 hex characters) i.e. “BBC8A374 E7B37BD0
CVT Continuously Variable Transmission
Wikipedia: Continuously variable transmission
Subaru name: Lineartronic
DCCD Drivers Control Center Differential
DENSO-C DENSO Interactive Information & Communication Diagnostic Tool; original equipment diesel service tool for independent garages
DOC Diesel Oxidation Catalyst
Wikipedia: Catalytic converter – Diesel engines Diesel Oxidation Catalyst
DPF Diesel Particulate Filter
Wikipedia: Diesel particulate filter Diesel Filter Regeneration
Like with Subaru, DPF casing often contains catalyst (DOC), upstream of actual filter.
Subaru diesel dashboard DPF Light: DPF Light
DRL Daytime Running Lights
DST-i Hardware interface between (laptop) computer and car OBDII port. Needed by OEM SSM4 Windows software. Connection: USB (2.0) or Bluetooth. Display: colour LCD screen. Can be used for diagnosis in stand-alone mode, not connected to a PC, requires special software on SD memory card.
Make: Denso
DTC Diagnostic Trouble Code
Wikipedia: Diagnostic Trouble Code
EPB Electronic Parking Brake
ECM Electronic Control Module. Another term for Electronic Control Unit.
ECU Engine Control Unit or Electronic Control Unit
EDM European Domestic Market
EEPROM Electrically Erasable Programmable Read-Only Memory. Type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed.
Control units often contain such a chip to store a few KB of data (important variables, settings, learned parameters), usually transferred via simple serial protocol. Some (modern) microcontrollers have data flash built-in, therefore no extra EEPROM chip is needed
Wikipedia: EEPROM
EGR Exhaust Gas Recirculation: nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines
Wikipedia: Exhaust Gas Recirculation
EGT Exhaust Gas Temperature
Most Boxer Diesel models are fitted with two EGT sensors, easily visible looking at DPF:

  1. Catalyst inlet
  2. DPF inlet

Exception: first generation models (unmanaged DPF, no sensors)
Wikipedia: Exhaust gas temperature

ETI Equipment and Tools Institute. Have to buy (expensive) membership to get car specific (diagnostic protocol) data, various OEMs, some require extra licenses.
ETC Electronic Throttle Control
EyeSight Camera based safety and driver assist system.
Subaru global: EyeSight
FAP filtre à particules (French term for DPF)
Feed Pump Integrated in high pressure (common rail) fuel pump (inside cylindrical cap at rear of pump where SCV is located).
Function: drawing diesel fuel from tank (through fuel filter), applying some initial pressure in order to properly feed SCV and then the plungers.
Type: gerotor (trochoid gear)
Make: Denso
HCE Hitachi Car Engineering Co., Ltd.; Hitachi Automotive Systems, Ltd.
HDS Hitachi Diagnostic System. The HDS tool provides the aftermarket with exact same functionality as the Subaru Dealer diagnostic tool Subaru Select Monitor III (SSM-III).
hex Hexadecimal (also base 16, or hex) is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols: 0-9 to represent values zero to nine, and A, B, C, D, E, F (or alternatively a, b, c, d, e, f) to represent values ten to fifteen. Hexadecimal numerals are widely used by computer systems designers and programmers. The prefix “0x” is common.
Wikipedia: hexadecimal
High Pressure Pump aka common rail pump, supply pump
Type for Euro 4/5 models: Denso HP3 (up to 180 MPa = 1800 bar = 26100 psi)
Purpose: Creating very high pressure needed for injectors, feeding common rail.
Contains a low pressure feed pump, as well as two high pressure plungers operating in parallel. Driven by helical gear (Euro 4/5) or chain (Euro 6) from crankshaft, speed ratio 1:1.
Electrical components, all connected to ECU: SCV, fuel temperature sensor (measuring at intake duct)
After changing entire high pressure pump, just SCV or ECU, “Fuel pump duty learning” procedure should be executed using tester software (SSM-III or SSM4).
ROM calibration: Stock Subaru diesel Euro 4/5 (?) use up to 1700 bar max pressure.
IAT Intake Air Temperature
ISC Idle Speed Control
JDM Japanese Domestic Market
LH Left Hand
LHD Left Hand Drive
Lineartronic Subaru’s name for its CVT; Petrol models since 2009, as for diesel it has been first available with 2013 Outback.

LSD Limited Slip Differential
Wikipedia: Limited-slip differential
LUT Look-Up Table
Wikipedia: Look-Up table
MAF Mass Air Flow
MAF sensor is usually located after air filter. On diesel models it provides both mass air flow [kg/h] and inlet air temperature [°C] to the ECU.
Wikipedia: Air flow meter
MAP Manifold Absolute Pressure
Wikipedia: MAP sensor
MCU Microcontroller Unit
Wikipedia: Microcontroller
MIL Malfunction Indicator Lamp (“Check Engine Light”) MIL
Wikipedia: Malfunction Indicator Lamp
MFD Multi-Function Display; center display (TFT screen, connected to combination meter via UART, also HS-CAN bus)
MT Manual Transmission
Wikipedia: Manual transmission
MY Model Year
Wikipedia: Model Year
NaN Not a Number; numeric data type value in computing of floating-point calculations representing an undefined or unrepresentable value
Wikipedia: NaN
NRC Negative Response Code = Error number in protocols
NSM New Select Monitor. Old handheld device for diagnostics and firmware updates.
NTC Negative Temperature Coefficient. NTC thermistors are often used for measuring temperatures.
Wikipedia: Negative Temperature Coefficient
OBD On-Board Diagnostics
Wikipedia: On-board diagnostics
PAK Pack file. Subaru specific file format used by OEM SSM-III software component FlashWrite for updating (reflashing) control unit firmware. Usually encrypted, can contain one or more ROMs incl. bootloader/kernel if applicable. PAK name corresponds to file name, correlating to software version.
PTC Positive Temperature Coefficient
Wikipedia: Positive Temperature Coefficient
PWM Pulse-width modulation
Wikipedia: Pulse-width modulation
QR Code Quick Response Code; matrix barcode (or two-dimensional barcode) first designed for the automotive industry in Japan, invented by Denso WAVE
Wikipedia: QR code
RAM Read & write memory, usually faster than EEPROM or ROM. Volatile, meaning stored information is lost if (battery) power is removed
Wikipedia: Random-access memory
RH Right Hand
RHD Right Hand Drive
ROM Software (firmware) of a control unit. Originally Read-Only memory, however in all modern vehicles the software can be rewritten (re-flashed). In very old cars chips had to be replaced in order to change the software.
ROMID Sort of Firmware-ID. Subaru specific ID consists of 5 bytes = 10 hex characters. Easy to retrieve via SSM protocol. RomRaider and EcuFlash software call this ECUID. Example: 6644D87507
Listing CALID + ECUID: RomRaider Forums – Stock ROM List
RR RomRaider.
Free open source software, originally for Subaru petrol, also supports diesel models.
SAE Society of Automotive Engineers
SCV Suction Control Valve; Valve attached to the high pressure (common rail) fuel pump to control its discharge quantity, therefore desired rail and finally injection pressure. It is of linear solenoid type, normally open, driven by PWM duty ratio signal ECU output. ROM confirms, Denso diesel software is configured to use 250 Hz waveform. At ignition on stage you might notice a humming noise from it – self test? If engine is not being started, ECU terminates output after 40 seconds.
When not powered, the valve’s return spring fully opens fuel flow to the plunger’s suction ducts, causing maximum discharge rate, high rail pressure. High duty output does the opposite, closes valve, resulting in less pump discharge, low rail pressure.
Positioning is determined through average electric current, monitoring and adjusting present vs. target value, respectively. Normally the system uses closed-loop operation.
Log items, RomRaider designations:

  • Fuel Pump Suction Control Valve Current (Target) [mA]
  • Fuel Pump Suction Control Valve Current (Actual) [mA]
  • Fuel Pump Suction Control Valve Learning Value [mA]
  • Fuel Pump Learning [Not Completed; Completed (normal)]

Euro 4 spec SCV current example values:

  • warm idling, 250 bar: 1770 mA
  • high RPM, high injection amount, 1500 bar: 1220 mA

Make: Denso, part number varies with Euro spec.

SDI Subaru Diagnostic Interface. Hardware interface between (laptop) computer and car OBDII port. Needed by OEM SSM-III Windows software. SDI is a little computer, can do some work in standalone mode.
SDR Subaru Driving Recorder
SIA Subaru of Indiana Automotive Inc. From wikipedia: In 1989, Subaru and then-partner Isuzu opened a joint factory in Lafayette, Indiana called Subaru-Isuzu Automotive, Inc., or SIA, which initially manufactured the Subaru Legacy and Isuzu Rodeo. In 2001, Isuzu sold their stake in the plant to FHI for $1 due to flagging sales and it was renamed Subaru of Indiana Automotive Inc. SIA has been designated a backyard wildlife Habitat by the National Wildlife Federation and has achieved a zero-landfill production designation.
SOA Subaru of America Inc.
SSM-III Subaru Select Monitor III. Subaru dealership OEM tester software. Made by Hitachi Car Engineering Co., Ltd. Windows PC based diagnostic application that uses the proprietary SDI interface hardware. Later versions also support Denso DST-i interface. Can communicate with various car control units using a bunch of different protocols.
Successor: SSM4
SSM4 Subaru Select Monitor 4. Subaru dealership OEM tester software; introduced in 2015, successor of SSM-III.
Windows PC based diagnostic application that uses the proprietary DST-i interface hardware.
Differences compared to predecessor:

  • made by Denso
  • SSM4 can only use Denso DST-i interface hardware
  • allows logging of multiple control units simultaneously
Sub Fuel Pump aka: fuel transfer pump
Electrical pump, located outside fuel tank near rear differential (Euro 4/5) or within tank (Euro 6, level sensor assembly).
Operated by ECU via relay, turned on shortly after engine start till engine stop.
Apparently its purpose is to circulate fuel inside fuel tank, indirectly powering jet pump which draws fuel from sub half (left) of saddle tank into main half (right).
The common rail high pressure pump is solely responsible for drawing fuel from the tank as it has an integrated feed pump.
Test/delivery mode operates pump using on/off pattern, rather audible, when engine is off.
SuperH, SH Processor architecture, originally developed by Hitachi, currently produced by Renesas.
Page ECU Hardware has details of various SH chips used in Subaru ECUs.
Wikipedia: SuperH
SVG Scalable Vector Graphics. SVG should be viewable in modern browsers like Firefox, Chrome, Opera, Internet Explorer 9+ (older IE need plug-in), various graphic viewers, vector graphics applications like Inkscape (free), Adobe Illustrator etc.
Wikipedia: Scalable Vector Graphics
SW Switch; in hardware or software, 2 states only: ON/OFF
TCU Transmission Control Unit
Wikipedia: Transmission control unit.
Subaru’s AT and Lineartronic (CVT) use a dedicated TCU. Similar to an ECU, its firmware can be updated, data logging is also supported.
On some (compact) cars, both TCU and ECU are combined into a single unit as powertrain control module (PCM).
Thermistor Type of resistor whose resistance is dependent on temperature, more so than in standard resistors. Often used as NTC temperature sensors.
Wikipedia: Thermistor
UDS Unified Diagnostic Services, ISO 14229; protocol for automotive diagnostics
Wikipedia: Unified Diagnostic Services
USDM United States Domestic Market
VDC, ESC, ESP, DSC Vehicle Dynamics Control, also Electronic Stability Control (ESC), Electronic Stability Program (ESP) or Dynamic Stability Control (DSC), is a computerized technology that improves a vehicle’s stability by detecting and reducing loss of traction (skidding).
Wikipedia: Electronic stability control
VGT Variable Geometry Turbocharger
Wikipedia: Variable geometry turbocharger
VIN Vehicle Identification Number
VIN or chassis number, is a unique code including a serial number, used by the automotive industry to identify individual vehicles.
10th digit = model year: 8 = 2008, 9 = 2009, A = 2010, B = 2011, C = 2012, D = 2013, E = 2014, F = 2015, G = 2016, H = 2017, (no ‘I’ !), J = 2018, K = 2019, L = 2020, …
Wikipedia: Vehicle identification number

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