What the immobiliser really does
The immobiliser is not a separate box you unplug. It is a conversation: the moment you switch on the ignition, the engine ECU queries the immobiliser unit (often built into the body computer or the instrument cluster), which has itself read the transponder in the key. If the answer is not what the ECU expects, it cuts injection. The starter turns, the engine never fires.
That check lives inside the ECU software, together with the paired vehicle identity. This is why a second-hand ECU — even one strictly identical to yours — will never start as it is: it is still waiting for the identity of its original car.
When it is the right call
There are four cases, and they are the only ones we take:
- A second-hand ECU fitted to another vehicle — by far the most common one.
- An engine outside the vehicle: test stand, buggy, boat, generator, swap project. There is no body computer and no key left to query.
- A failed immobiliser unit on an otherwise healthy vehicle, where replacing it costs more than the car is worth.
- A competition vehicle or closed-circuit use, where the original electronics have been stripped out.
When the answer has to be no
Let us be blunt: we turn down requests that look like a way around ownership. A wiped serial number, a vehicle nobody can say anything about, an “urgent” request with no registration document and no explanation — that is a no, and it stays a no even when the file is technically doable.
This is not excessive caution. An Immo Off is asked for by a mechanic with a used ECU on the bench, and by someone who does not have the key to the car. The difference shows immediately in how the request is written.
What makes a file feasible
Feasibility depends neither on the make nor on the year, but on the ECU and on the quality of the read. The three questions that decide it:
| Item | What we look at | Why |
|---|---|---|
| The ECU | ME7, EDC15, EDC16, EDC17, MED17, SID, Delphi, Siemens… | The immo routine is specific to each family. The common ones are documented; the rare ones need analysis. |
| The read | Full or partial, EEPROM included or not | On many ECUs the pairing lives in the EEPROM, not in the flash. A partial OBD read is then not enough. |
| The origin | An original file, not one already modified | A file already remapped by someone else may carry a broken checksum or a relocated area. |
If you do not know which ECU you have, the reference is on the label stuck to it — something like 0281015029 or 03L906023. It is the only piece of information that is genuinely essential.
How it works
Four steps, and nothing to pay before the third:
- You send your original file with the make, the model and the ECU reference.
- We check feasibility within the hour. Not an automated acknowledgement: someone opens the file and looks.
- If it is feasible, you get the confirmation and the payment link — €19.95.
- The modified file follows. If it is not feasible, you pay nothing and we tell you why.
🔓 Send a file for checking
Feasibility checked within the hour, €19.95, and nothing to pay if it cannot be done.
What the law says
In most of Europe an electronic immobiliser is mandatory at first registration for the vehicles concerned. Removing it from a vehicle used on public roads is not a trivial operation: it takes the vehicle outside its type-approved configuration, and it can be held against you after an accident or an inspection.
On an engine outside a vehicle, on closed-circuit machinery or on a competition car, the question does not arise in the same terms — there is no road approval left to preserve.
We supply a file. How it is used, and whether that use is compliant, is on whoever installs it. If the subject interests you beyond this paragraph, it is covered in detail in the legal and liability course.
In short
The immobiliser is a software check, not a part. Removing it is therefore done in the file, without changing anything else about how the engine runs.
It is the right answer for a second-hand ECU, an engine outside a vehicle or a dead immobiliser unit. It is not the right answer for getting around a missing key on a car nobody can account for — and technical feasibility changes nothing about that.
When in doubt, checking costs nothing: send the file and you will know within the hour.