A swapped engine that cranks strongly and will not fire is, more often than not, an engine computer waiting for an immobiliser release that the new vehicle cannot send. As of October 2026 there are three routes that work — bring the matched set from the donor, marry the computer to the new car in a programming session from $100 to $250, or remove the check with an IMMO-OFF file at $100 to $150 — and which one is open to you depends entirely on the platform.
We cover fewer platforms than a swap forum would lead you to hope. This post sets out which ones, what each route costs, and how to choose before the engine is in the bay and not after.
Why this catches people out
An engine swap is planned around mounts, cooling, driveshafts and wiring. The immobiliser tends to surface at the first start attempt, because it produces no symptom until then.
On most vehicles built since the mid 1990s, the engine computer will not run the engine on its own authority. A separate module — in the steering column, the instrument cluster, the body computer or a dedicated box — reads the key and tells the engine computer that this start is allowed. Move the engine and its computer into another vehicle and that conversation has no other party. The starter turns, because the new car's starting circuit is its own. The computer, hearing nothing, withholds fuel or spark.
Everything else about the swap can be perfect and the result is identical to a failed fuel pump. Hours are lost to fuel pressure and crank sensors before anyone looks at the security lamp. Our security light, no start diagnosis post sorts the symptom into branches; on a swap, the branch is nearly always this one.
Route one: bring the matched set
The engine computer, the immobiliser module and the key were programmed to each other at the factory. If all three come from the same donor and all three can be wired into the new vehicle, the immobiliser keeps working exactly as it did.
This is the route nobody sells, because there is nothing to sell. It is frequently the best one.
It suits a swap where you are buying a complete donor, or pulling from a car you can strip yourself. Take the engine computer, the immobiliser module, the key or keys, the reader coil or antenna around the ignition lock, and — where the cluster is part of the chain — the instrument cluster.
It does not suit an engine bought on a pallet with only its computer, a donor that has already been parted out, or a build where the donor's lock cylinder and reader have no sensible place to live in the new car.
The engineering advantage is real. The car keeps an anti-theft system, nothing in the computer's software has been altered, and there is no later question about what was changed. If the parts are available, cost the wiring before you assume a file is simpler.
Route two: marry the computer to the new car
Where the engine is going into a vehicle of the same manufacturer and the same broad generation, the new vehicle often has its own immobiliser that the engine computer can be taught to accept. This is what a manufacturer's programming application does when a dealer replaces a failed engine computer, and it is what our remote sessions run.
| Platform | Factory application | Session price |
|---|---|---|
| GM | ACDelco TDS | $100 |
| Ford / Lincoln | FJDS / FDRS | $150 |
| Nissan / Infiniti | CONSULT III Plus | $150 |
| Mazda | MDARS / M-MDS | $150 |
| Volvo | VIDA | $250 |
| Toyota / Lexus | TIS Techstream | $250 |
| VW / Audi | ODIS | $250 |
| Chrysler / Dodge / Jeep / Ram | wiTECH 2 | $250 |
A session works only inside the manufacturer's own rules. It will program a computer the factory application recognises as belonging in that vehicle, and it will run the immobiliser learn the application offers. It will not persuade the application to accept an engine computer from a different model family that the factory never paired with that body. A like-for-like engine replacement, or a swap between closely related models, is session work. A cross-generation or cross-make transplant usually is not.
Mopar carries one planning caveat: first-time setup takes about 24 hours for J2534 registration, so the first booking cannot be a same-day rescue. And not every procedure exists on every vehicle — coverage varies by model year, module and the manufacturer's security requirements — so tell us the donor and the recipient before you book.
Route three: remove the check
When there is no matched set to move and no factory route that will pair the two, the remaining option is to change the engine computer so it no longer waits for a release. That is what IMMO-OFF means, and our IMMO-OFF cost guide covers it in general terms.
The honest part is the coverage. An instant file exists only where we have verified the change against real files from running cars. As of October 2026 that is:
- VW and Audi 1.8T-era Bosch ME7 — the immobiliser EEPROM on ME7.1, ME7.1.1 and ME7.5. This is the computer in a very large share of transplanted four-cylinder turbo engines, and our ME7 guide covers reading the chip.
- BMW MS43 on software ca430064 — the M54 six-cylinder, a common transplant engine. Other MS43 software versions are mail-in. See our MS43 guide.
- BMW MS45 on DME part 6577365 and BMW ME7.2 on part 7506366 — covered in our MS45 and ME7.2 post.
- GM memcal, 1986 to 1993 — tuned-port and LT1 calibrations on the $8D and $DA3 masks. See our VATS delete guide.
Instant files run from $100 to $150 depending on the product, shown on the calculator page before you pay. Each calculator checks the uploaded file against the software it was verified on and refuses anything else before payment.
Several families people ask about are not on that list, and the status of each is published on our coverage matrix. Bosch MED17, EDC17 and Simos18 have checksum correction live and IMMO-OFF listed as coming, not available. Saab Trionic is mail-in only. Simos PCR2.1 is RSA-signed and not supported. A late-model GM, Ford or Mopar engine computer is not on the file list at all: those platforms are session work, and on signed controllers there may be no file route from anyone. Our live, beta and soon post explains what each status means.
“The swap community has a habit of saying a computer can be done when what they mean is somebody did one once. We publish what we have verified on running cars, and the list is shorter than the forum's.” — File-service desk, ECU Flash Cartel
Choosing between them
Four questions settle it.
Do you have the donor's immobiliser module and key? If yes, route one is available and worth pricing first.
Are the donor and recipient the same manufacturer and a closely related model? If yes, a session may marry the computer to the new car's own immobiliser, and the car keeps anti-theft protection.
Is the engine computer on the instant list? If yes, a file is the fastest route and you need only a tool that can read and write the chip or flash.
None of the above? Mail-in bench work at $250 reaches further than the instant path, because a person does the work and checks it. Beyond that, post the job to our specialist network: it costs nothing, operators with different tooling bid, and you pay only if you accept one.
Ask these before buying the engine, not after. The cheapest moment to choose route one is while the donor car is still whole.
What removing the check does not solve
An IMMO-OFF file removes one obstacle. Swaps have several others that produce the same symptom, and our swapped ECU won't start post lists them. The ones that appear most on transplants:
- Missing network partners. A computer that expects to hear from a transmission controller, an ABS unit or a cluster may run in a reduced mode or log communication faults without them. That is a wiring and configuration matter, not an immobiliser one, and our U0100 guide covers it.
- VIN mismatch. Modules that compare VINs will complain. Our VIN mismatch post explains which ones care.
- The starter side. On several platforms the immobiliser module controls the starter through its own circuit. In a transplant the new vehicle's starting circuit usually takes over, but on an original car with a deleted check and a failed module, the engine may still not crank.
- Calibration. The file changes nothing about fuelling or ignition. A swapped engine with different intake, exhaust or gearing may need tuning, and that is a separate job from a separate specialist.
Reading the computer
Routes two and three both begin with knowing exactly which computer you have, and route three needs a complete read of it.
Identify by the label, not by the engine. The same engine ran different computers across years and markets, and the label is the only thing that settles it. Our free identifier takes a label photo or a file.
Which access level a read needs is family-dependent. Our bench, boot and OBD read methods guide sets out what each reaches. The EEPROM on an ME7 and the memcal chip on an early GM are both chip-level reads that predate diagnostic-port access; the BMW families are external-flash reads.
Whatever the method, read twice, compare the two files, and keep the original. It is the only thing that restores the computer exactly as it was, and our return ECU to stock post explains why that file is the most valuable artefact in the job.
A checklist before you buy the engine
Most immobiliser trouble on a swap is decided at the point of purchase, when nobody is thinking about it. Before money changes hands:
- Get the engine computer's label, not just the engine code. A photograph of the whole label tells you the family, the part number and usually the software, and those decide which of the three routes exists.
- Ask what else comes with it. The immobiliser module, the key, the reader coil and the cluster are worth far more to you with the engine than they are to the seller without it.
- Check the computer against the instant list by running the label through our identifier. A computer that is on the list is a known cost. One that is not is an open question you are choosing to buy.
- Decide whether the car keeps an immobiliser. A daily-driven car parked on the street has a different answer from a track car on a trailer.
- Budget the read. Route three needs a tool that can read and write that specific computer, or a mail-in.
Five minutes with a label photo before purchase is cheaper than any of the routes after it.
Ownership and the legal position
We require proof of ownership for any operation that touches an immobiliser chain, on every make. On a swap that is normally a title for the vehicle and a receipt for the engine. Theft-claim data published by the Insurance Institute for Highway Safety shows how directly immobiliser design affects theft rates, which is the reason the question is asked and the reason it is not a formality.
We do not provide emissions defeat, delete files, or services intended to bypass emissions laws. Our services exist for tuning preparation, diagnostics, repair, motorsport, and off-road use where legally permitted. Customer is responsible for confirming legal use in their location and application.
An engine swap has its own regulatory side. The federal Clean Air Act governs emissions equipment and calibration on road vehicles, and states apply their own rules on which engines may go into which vehicles and what inspection follows. An immobiliser change is not an emissions change, but the rest of the swap is yours to confirm with your state before the car returns to the road.
The short version
A swapped engine that cranks and will not fire is usually waiting on an immobiliser. Bring the donor's computer, module and key as a set if you can. Marry the computer to the new car with a session, from $100 to $250, if the two are closely related. Otherwise an IMMO-OFF file at $100 to $150 covers a short, verified list — ME7, three BMW computers and early GM memcals — with mail-in at $250 and the specialist network behind it. Decide while the donor is still in one piece, and check the calculators before you buy the engine.