ECU file and WinOLS glossary: the terms explained

The world of ECU files has its own vocabulary, mixed from automotive engineering, electronics and the habits of individual tools. This glossary explains the terms that come up most often around original files, reading methods and WinOLS map packs — briefly, and without jargon where possible.

A – C

A2L: The standard file format (ASAM MCD-2 MC) in which manufacturers describe an ECU software's variables and maps. Often loosely called a damos.
Axis: The breakpoints along one side of a curve or map — for example engine speeds along X and loads along Y. Stored in the file like the map data, with its own data organisation and factor. See how map axes and factors work.
BDM: Background Debug Mode: a debug interface of Motorola/Freescale processors, used to read and write older PowerPC-based ECUs such as Bosch EDC16 and MED9 directly on the circuit board.
Bench read: Reading an ECU removed from the vehicle, connected to the tool through its own connector. Usually gives more of the memory than OBD. See read methods.
Bin file: A plain binary image of memory, usually with the extension .bin: the bytes as they are stored, with no header.
Boot mode: A start-up mode of the microcontroller in which it accepts a small program over a serial line instead of running its flash. Used for complete reads with the housing open.
Breakpoint: One value on an axis; the ECU interpolates between neighbouring breakpoints.
Byte order: Whether multi-byte numbers are stored low byte first (Lo/Hi, little-endian) or high byte first (Hi/Lo, big-endian). Depends on the processor.
CAL ID: Calibration identification: the ID of the installed calibration, which OBD-II / EOBD vehicles report to any scan tool. On Toyota and many other makes it is the best way to identify the software.
Calibration: The data part of the ECU software — constants, curves and maps — as opposed to program code. Also the dataset of one particular engine variant.
Checksum: A value calculated over an area of memory that the ECU uses to verify that the area is intact. Changing data without correcting the checksums typically makes the ECU reject the software.
Common rail: Diesel injection system with one high-pressure rail feeding all injectors; the ECU controls the rail pressure and each injection.
Count word: A number stored directly before an axis that tells how many breakpoints follow. Common in many ECU families.
CVN: Calibration Verification Number: a checksum-like value over the calibration that OBD-II / EOBD vehicles report. A different CVN means different calibration data.

D – F

Damos: A manufacturer's description of an ECU software (often in A2L format), naming every variable and map. Exists only for some versions.
Data flash: A flash area of the processor used to store changing, unit-specific data, often emulating an EEPROM.
Data organisation: How a value is stored: width (8, 16, 32 bit or float), byte order and signed or unsigned. WinOLS calls this the map's data organisation.
DDE / DME: BMW's names for its diesel (Digital Diesel Electronics) and petrol (Digital Motor Electronics) engine ECUs.
Driver's wish: The map that turns pedal position and engine speed into a requested torque or fuel quantity.
DTC: Diagnostic trouble code: a fault code the ECU stores when it detects a problem, read with a diagnostic tool.
Dump: Informal word for a read of a memory — a flash dump, an EEPROM dump.
ECU: Electronic control unit; in this context usually the engine control unit (also ECM, DME or DDE).
EDC: Electronic Diesel Control: Bosch's family name for diesel ECUs, followed by the generation (EDC15, EDC16, EDC17). See Bosch EDC17 explained.
EDU: Electronic driver unit: on some diesels (many Toyota common-rail engines, for example) a separate box that drives the injectors. It is not the engine ECU.
EEPROM: Small non-volatile memory for data that changes during the vehicle's life — adaptations, counters, coding, immobiliser data. Specific to one unit.
Factor and offset: The conversion from raw stored numbers to physical values: physical = raw × factor + offset.
Flash memory: The non-volatile memory that holds the ECU's program and calibration; it is what "flashing" rewrites.

H – M

Hex editor: A program that shows a file byte by byte in hexadecimal and as text. The simplest tool to compare two ECU files.
HW number: The part number of the physical control unit. One HW number usually runs many software versions. See how to find the HW and SW number.
Immobiliser: The anti-theft system that lets the engine run only with an authorised key. Its data in the ECU is unit-specific and lives in EEPROM or data flash.
JTAG: A standard debug and test interface found on many processors and boards; on some ECUs it gives direct access to the memory.
K-line: An older single-wire diagnostic connection, used before CAN became standard for diagnostics.
KWP2000: Keyword Protocol 2000, an older diagnostic protocol (ISO 14230) used over K-line and CAN.
Map: A table of values over two axes, such as boost target over engine speed and injection quantity. A table over one axis is a curve.
Map pack: A set of map definitions — names, addresses, sizes, data organisation, factors and axes — for one software version. It changes no values. See what a WinOLS map pack is.
MD1 / MG1: Bosch's newer generation of diesel (MD1) and petrol (MG1) engine ECUs, successors of EDC17 and MED17.
ME / MED / MEVD: Bosch petrol ECU families (MED for direct injection, MEVD with variable valve control), followed by the generation, such as MED17.

O – S

OBD: On-board diagnostics: the vehicle's diagnostic system and its 16-pin socket. "Reading over OBD" means reading through that socket without removing the ECU.
Original file (ori, stock file): The ECU software exactly as the vehicle manufacturer released it, without modifications. See what an original ECU file is.
Padding: Filler bytes (usually FF or 00) in unused memory areas or at the ends of axes.
Rail pressure: The fuel pressure in a common-rail system, set by the ECU according to its maps.
Read: Copying an ECU's memory into a file — also the file that results.
Signed value: A number stored so that it can be negative. The same bytes read unsigned give a large positive number instead.
Smoke limiter: A diesel map that limits the injected quantity according to the available air, to keep smoke within limits.
SW number: The identification of the software version in the ECU — the number that decides which original file matches.
SW upgrade: An identifier of a later software update, listed separately on some file pages.

T – W

Torque limiter: A map or set of maps capping the engine torque — often per gear, by engine speed or by conditions such as temperature.
TriCore: Infineon's family of automotive microcontrollers used in Bosch EDC17, MED17 and many other ECUs. Little-endian.
UDS: Unified Diagnostic Services (ISO 14229), the diagnostic protocol of most current vehicles, usually over CAN. Reading and writing over OBD use its services.
Variant: The specific hardware and software project within an ECU family — for example C46 in EDC17C46. Files of different variants are not interchangeable.
Version (WinOLS): One state of a file inside a WinOLS project — for example the original and a modified version side by side for comparison.
WinOLS: EVC electronic's program for viewing, comparing and editing ECU data, and for working with map definitions.
Write (flash): Transferring a file into the ECU's memory. The opposite of a read, and the step where most care is needed — see how to check you have the right original.

Missing a term? The guides in the articles section go into more depth. To find a file, search by HW or SW number with the search box at the top of the page, or browse by vehicle make or ECU type.