Will a remap fail an MOT?
No. The MOT does not inspect engine software, and a Stage 1 remap leaves the emissions equipment in place and working. The exception is software that switches off emissions equipment, meaning an AdBlue, DPF or EGR delete, which will not pass the test. A performance or economy remap is neither of those.
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An MOT tester checks what the car does and what is fitted to it. They do not read the engine ECU, compare software versions or look for evidence of tuning. There is no part of the inspection that would tell a tester a Stage 1 remap had been done, and no item in the manual that fails a vehicle for one. A remapped car with its emissions equipment intact and working passes or fails the MOT on exactly the same grounds as a standard one.
The emissions test
The one place a remap could show is the emissions test, and a Stage 1 file should not show there either. A diesel is tested for smoke opacity under a free acceleration; a petrol for CO, hydrocarbons and lambda at idle and fast idle. A properly written Stage 1 file keeps fuelling within the range the catalyst, the DPF and the SCR system were designed for, so the results are in the same place they were before. A crude file that over-fuels a diesel for the headline figure can smoke, and since May 2018 any visible smoke from a diesel is a failure. That is a bad file, not a remap as such, and it is one of the reasons to ask to see your figures before you book.
Warning lamps
An illuminated engine management lamp, or an emissions warning, is a failure in its own right. A Stage 1 remap does not light one. A car that already had a fault before the remap still has it afterwards, and that is why we scan before and after. The remap is not the cause, but it is the last thing that happened and it would get the blame.
The exception: emissions deletes
Software that switches off the AdBlue system, stops the DPF regenerating or holds the EGR valve shut is not a remap in the sense this page means, though it is often sold alongside one. It changes what the emissions equipment does, and that is what the MOT checks. Since May 2018 testers look for evidence that emissions equipment has been removed or tampered with, and the DPF's presence has been checked since February 2014. Those jobs have their own pages, the legal position is on its own page, and they are the reason this page exists. People hear "remap" and "delete" in the same breath and assume the MOT treats them the same. It does not.
What a tester can see
Nothing, on a Stage 1 car. A dealer with the manufacturer's diagnostic tool can compare the software identifier in the ECU with what it expects, and that is a warranty question, not an MOT one. The MOT tester's equipment is an emissions analyser, a brake tester and a pair of eyes.
Insurance is the one you should be thinking about
Not the MOT. A remap is a modification and your insurer needs to know about it. Most insurers add little or nothing for a Stage 1, but an undeclared one can void the policy. Declare it and then forget about it.
What matters, in three lines
Passes, nothing to see
There is no software inspection in the MOT. The emissions equipment is intact and working and the emissions results are where they were. The tester cannot tell.
AdBlue, DPF and EGR deletes fail
They change what the emissions equipment does, and that is checked. Tampering has been looked for since 2018 and the DPF's presence since 2014. The legal position has its own page.
Tell your insurer
A remap is a modification. If you declare it, it usually costs little or nothing. If you do not, it can void the policy, which matters far more than a test certificate.
Related questions
Can an MOT tester tell my car is remapped?
No. The test has no software inspection. The tester sees emissions results, lamps, brakes, tyres and the rest of the manual. A Stage 1 car with working emissions equipment looks like a standard one to every piece of equipment in the test bay.
My car smoked on the emissions test after a remap. Why?
Either the file over-fuels, which makes it a bad file that should be replaced, or something else was already wrong, such as a tired injector, a sticking EGR valve or a DPF that is loading up. Any visible smoke from a diesel has been a failure since 2018. Get the codes read before blaming the map; if it is the map, we will put the original back free and refund it.
Does a gearbox remap affect the MOT?
No. Gearbox software has no bearing on anything the MOT tests.
Is a pops and bangs map an MOT problem?
It can be. Those maps often change ignition timing on the overrun in ways that raise emissions and can light lamps, and some are loud enough to fail on noise. We do not fit them to road cars and would not recommend one for a car that needs an MOT.
Get my price
Registration, what you would like done, and where you are. We come back with a fixed price, usually the same day, and a booking link if you want to go ahead.
- From £245, quoted on the car
- Fully insured, at your home or work
- No workshop visit, no courtesy car needed
Where to go next
Will a remap void my warranty?
It can. What a manufacturer can and cannot refuse, and what we do about it.
Read more → The exception explainedIs an AdBlue delete legal in the UK?
Regulation 61A, where a delete is lawful, the MOT, and what the DfT has proposed.
Read more → See for yourselfYour car's figures
Put the registration in and see what your engine makes now and what a Stage 1 file gives it.
Read more →