Immo off and ECU virginisation: everything you need to know

What the immobiliser is for

On any modern vehicle, the key contains a transponder. When starting, the vehicle's immobiliser module (BSI on PSA, UCH on Renault, Kessy or immobilizer on VAG) queries the key, then communicates with the engine ECU. If the ECU does not recognise the code it receives, it cuts the injection: the engine turns over on the starter but does not fire up.

This communication relies on pairing between the ECU and the vehicle. As soon as this pairing is broken, the engine will no longer start. This happens when you fit a used ECU from another car, when the immobiliser module fails, when the keys are lost, or when you install a complete engine in another vehicle.

Immo off: disabling the check

Immo off involves modifying the ECU program so that the immobiliser check is no longer carried out. The ECU stops waiting for a response from the module and allows injection in all cases. The engine then starts with any mechanical key, without electronic recognition.

This is the solution chosen when the pairing cannot be restored: immobiliser module out of order and unobtainable, lost keys with no possibility of recoding, a used ECU of unknown origin, fitting an engine on a test bench or in a competition vehicle, or an engine swap with an incomplete wiring harness.

Worth knowing before choosing this option: immo off removes an anti-theft protection from your vehicle. This is your decision as the owner, and it is up to you to assess the consequences, particularly with regard to your insurer. On a roadgoing vehicle in working order whose immobiliser functions, virginisation is almost always the better choice.

Virginisation: starting from scratch

Virginisation erases the pairing stored in the ECU and returns it to its factory-fresh state, before it was matched to a vehicle. The ECU is then said to be virgin: it can be paired again, via diagnostics, to the vehicle it is fitted to.

The key difference from immo off: the immobiliser remains active. Your vehicle keeps its anti-theft protection and continues to work with its coded keys. It is the clean solution when you fit a used ECU to a car whose immobiliser system is in good working order.

Its only limitation is technical: virginisation cannot be performed on every part number. On some ECUs, only immo off is possible.

Immo off or virginisation: which to choose

The two services are mutually exclusive: either the check is disabled, or the ECU is reset to a virgin state so it can be re-paired. Not both.

Memory types and the file to supply

If you send us a file rather than the part, it still has to be the right one. These terms indicate which type of read is needed to work on your ECU. Your reading tool tells you which one it produces.

MPC and FULL READ are not the same thing. MPC refers to the processor area; FULL READ is a complete backup that may contain several memories. If in doubt, send everything your tool has produced.

Two ways to have the work carried out

You have the equipment: send the file

If you have a reading tool and know how to read and rewrite your ECU, simply send us the file via our File Service. We send you back the modified file and you write it back. Price depending on your ECU part number: €70, €90, €120, or €170 for Bosch MD1 and MG1.

You don't have the equipment: send the ECU

You remove your ECU and ship it to us. We read it, modify it and rewrite it on the bench, then send it back ready to refit, return postage included. Price: €99, €139, €189, or €249 for Bosch MD1 and MG1. No tool is needed on your side, and we cover the whole of France. See the product: ECU immo off by post.

In both cases, the price depends on the reading method your ECU requires: a simple EEPROM does not involve the same work as a TriCore accessible only in boot mode.

The ECUs we cover

Our coverage includes 285 ECU references: 270 can be handled for immo off and 150 for virginisation, from Bosch, Siemens, Marelli, Delphi, Continental, Valeo, Sagem, Hitachi, Denso, Delco and Visteon. The best-covered makes are the VAG group, PSA, Renault, Dacia, Nissan, Fiat, Alfa Romeo and Lancia.

We also handle the latest-generation Bosch ECUs, which few workshops offer: MD1CS003 and MG1CS042 found on recent PSA models, including the entire 1.5 BlueHDi range, MD1CS006 on Renault, Dacia and Nissan, as well as MG1CS002, MG1CS008, MD1CS004, MD1CP004 and MD1CP014 on the VAG group, Porsche and Ford.

If your part number is not in our lists, state it when ordering: we will check feasibility and confirm the price before any work is carried out.

Terms of service

These services are reserved for vehicles you own and for legitimate breakdown cases: faulty immobiliser, lost keys, used ECU, engine swap. A copy of the vehicle registration document and of a piece of ID is required with every order.

The MOT (technical inspection) does not include a check of the immobiliser system. However, removing an anti-theft protection is your responsibility as the owner; if your vehicle is insured against theft, check with your insurer before choosing immo off rather than virginisation.