The three numbers on most ECUs
Take a Bosch diesel ECU from a Volkswagen. Its label can show three different numbers:
- The hardware number, from the company that built the ECU. On a Bosch unit it has ten digits, printed in groups, like 0 281 016 244. It describes the unit itself: the box and the circuit board inside it.
- The software number. On Bosch units it usually starts with 1037, like 1037 523 845. It names the program the ECU runs.
- The carmaker’s part number. Volkswagen’s look like 03L 906 022 LB. It’s the number the car brand sells the ECU under.
Those three examples come from the made-up file on our home page, not from a real car, but the formats are real. Other ECU makers use their own formats. The idea is the same: one number for the hardware, one for the software, one from the carmaker (Autotuner).
Hardware number or software number?
The hardware number belongs to the physical unit and doesn’t change when someone remaps the engine. The software is the part a remap changes (Dacodac). That’s also why a software number on its own can’t tell you whether the program was changed: it’s a name, not a check. To see a change you compare the file with another read, or, on a car, compare its software fingerprint with other cars running the same software.
Where to find them
1. On the ECU’s label
Where the ECU sits depends on the car. It can be under the dashboard, behind a trim panel or in the engine bay. The label usually shows the maker’s hardware number and the carmaker’s part number. Volkswagen Group labels can also show the engine code and the software and hardware versions (Autotuner).
2. With a diagnostic tool
Dealer tools, and tools like VCDS for Volkswagen Group cars, read the software part number and its version straight from the ECU. On those cars it’s called the box code (APR, 034Motorsport). In UDS, the diagnostic language most modern ECUs speak, the software number and the hardware number each have their own code, F189 and F191 (pyudskit).
A cheap OBD adapter can read something simpler: the calibration ID, the name of the program, which emissions rules make cars report (California BAR). Our car check reads it from the browser.
3. Inside a read of the ECU
If you or a tuner has read the ECU, most of the numbers are written inside the file. Which ones depends on the ECU family: Bosch ME7 and MED9 files hold the hardware number, EDC15 and EDC17 files don’t (OpenRemap). Drop the file on EcuInside and you get each number along with the exact bytes it came from.
4. From the VIN, at a dealer
A dealer’s parts department can look up the ECU’s part number from the car’s VIN (Goldfarb, Module Mechanics). That tells you what the car was built with. If the ECU was ever replaced, the one in the car can be different.
Reading a Bosch number
The first four digits of a Bosch hardware number say a lot: 0 281 is a diesel ECU and 0 261 a petrol one (Autotuner). Software numbers mostly start with 1037. Peugeot and Citroën EDC16C34 units use 1039, and some older families use other prefixes (OpenRemap). The full rules, family by family, are in Bosch ECU numbers explained.
Reading a Volkswagen Group part number
Read 03L 906 022 LB in four parts: 03L, 906, 022 and LB. The middle part puts it in the parts catalogue, and 906 is the group for engine control units. The letters at the end are the version (Darkside Developments, Actronics). This is how parts people and tuners read these numbers. Volkswagen doesn’t publish the rules.
Who makes the ECU
Bosch is the name you’ll see most, but not the only one. Siemens VDO became part of Continental in 2007, and Continental’s engine electronics became Vitesco in 2019. Delphi’s went to Delphi Technologies in 2017 and then to BorgWarner in 2020, and the Delphi name stayed on the units. Marelli builds ECUs for Fiat’s MultiAir engines, Denso for Toyota, Mazda, Mitsubishi and Nissan, and Hitachi’s now come from Hitachi Astemo, which also took in Keihin (Autotuner). Each of them numbers its units its own way, so the first job is always to work out who made the box.
Numbers change over time
Carmakers replace software versions, so a part number can be superseded by a newer one. Darkside Developments gives 04L 906 056 FB becoming KF as an example (Darkside Developments). When you buy a used ECU, match the carmaker’s part number and the software, and ask whether it will need programming to work in your car (Module Mechanics).
Have a read of the ECU? Drop it on EcuInside and see its numbers, the bytes they came from, and whether it looks like a whole read. Free, and the file isn’t kept.