MOT advisory explained
“Exhaust noisy”
The one advisory that is usually there by choice. Testers write it when an exhaust is louder than standard but not, in their judgement, excessively so, and the notes make clear what they are mostly looking at: sports back boxes, end cans and removed baffles. Four in ten owners get it again next year and are presumably fine with that.
The tester listened to the exhaust at idle and under a rev and judged it noticeably louder than the standard system for the car, but not so loud as to be excessive. There is no meter in an MOT. It is one person’s ear against their memory of what the car should sound like.
0.9% fail on exhaust noise at the next test, among the lowest figures for any advisory, and 39.7% are advised again. Owners who fitted a loud exhaust rarely take it off, and testers rarely fail one that is merely loud.
A noisy exhaust that was not chosen is a different matter. If the car has its original system and has become loud, something has failed: a silencer that has rusted through inside or a flexible section that has split. That is the exhaust leak advisory in waiting, and it fails ten times as often as this one.
An “exhaust noisy” advisory means the tester judged the exhaust louder than the standard system for the vehicle but not excessively loud, so the car passes. It is most often written on cars with an aftermarket sports exhaust or a silencer with the baffle removed. According to DVSA MOT data analysed by PriceMyRepair, only 0.9% of 382,681 such advisories followed to the next test failed on exhaust noise, and 39.7% were given the same advisory again.
What the tester is judging
No decibel limit. The MOT does not measure exhaust noise. The tester compares the sound with what a standard system on that vehicle would produce and decides whether it is louder, and if so whether it is excessively louder. Only the second is a failure. That leaves a wide band of loud-but-legal, and this advisory is what fills it.
What the notes say. “baffle fitted”, “exhaust not standard”, “slightly more than std”, “end can”, “aftermarket silencer fitted”, “no markings found”. Nearly every common note is about the system not being the original. A removable baffle in the tailpipe is the classic case: with it in, the car passes clean, and testers sometimes note whether it was fitted on the day.
The two kinds of noisy. An aftermarket system is loud by design and stays that way. An original system that has become loud has a silencer whose internal baffles have rusted away, or a split flexible joint near the engine. The second kind gets louder every month, smells of fumes at idle, and will fail as a leak long before anyone fails it for noise.
Will it fail next year?
There is one wording, recorded 743,154 times. 382,681 of those can be followed to the same vehicle’s next MOT.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 0.9% |
| Same advisory recorded again | 39.7% |
According to DVSA MOT data analysed by PriceMyRepair: 382,681 advisories followed to the same vehicle’s next test. Rows can overlap.
Fewer than one in a hundred fail on noise the following year. It is the lowest figure among the exhaust advisories by a distance: a minor leak fails 9.0% of the time and a defective mounting 5.5%. A loud exhaust is a stable state. A leaking one is not.
The repeat rate is among the highest we have measured. Two in five come back with the same note. That is not neglect. It is an owner who paid for the noise.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Exhaust emits excessive smoke or vapour | 9.4% | 14.2% | 153,116 |
| Exhaust has a minor leak of exhaust gases | 9.0% | 26.5% | 3,311,485 |
| Exhaust mounting defective | 5.5% | 23.3% | 1,459,563 |
| Registration plate deteriorated | 3.7% | 40.1% | 4,283,862 |
| Engine mounting damaged | 2.2% | 13.6% | 101,134 |
| Exhaust noisy | 0.9% | 39.7% | 382,681 |
| Undertray not fully secure | 0.6% | 8.6% | 83,373 |
The rate is flat at around 1.3 per 1,000 tests for the first ten years, then climbs to 10.4 on vehicles of 20 years and over. The oldest band is where modified and classic vehicles cluster. The failure rate does not move at all: under one per cent at every age.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 3–4 years | 1.3 | 0.9% | 36,292 |
| 5–6 years | 1.3 | 0.9% | 39,405 |
| 7–9 years | 1.3 | 0.9% | 53,927 |
| 10–12 years | 1.6 | 0.9% | 53,184 |
| 13–15 years | 2.3 | 0.9% | 57,916 |
| 16–19 years | 4.0 | 0.9% | 63,861 |
| 20 years and over | 10.4 | 0.7% | 62,333 |
Testers are told to fail an exhaust that is excessively noisy, and the guidance leaves excessive to their judgement. In practice a system that is clearly louder than standard but not painful passes with this note. One that drowns out conversation at idle, or has no silencer at all, does not.
If you run a system with a removable baffle, put it in for the test. It costs nothing, and it removes the one thing that turns this advisory into a fail on a strict day.
Noise is also a police matter, separate from the MOT. A car deemed excessively noisy on the road can be given a fixed penalty or a notice to fix it, regardless of what the certificate says.
Exact wording on your certificate
One advisory, one failure, and the difference is a single word.
| Line on the certificate | Result | Code |
|---|---|---|
| Exhaust noisy | Advisory — pass | 8.1.1 (a) |
| Exhaust noise levels in excess of those permitted | Major — fail | 8.1.1 (a) |
Nearly nine in ten have no position recorded, because noise has no position. Where one is given it is the rear, meaning the silencer or the tailpipe.
| Position written by the tester | Share of all instances |
|---|---|
| No position recorded | 87% |
| Rear | 7% |
| Offside rear | 2% |
| Front | 1% |
| Central | 0% |
| Offside | 0% |
From 743,154 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “baffle fitted” (1,114), “exhaust noisy” (1,041), “exhaust not standard” (654), “slightly more than std” (615), “silencer” (550), “end can” (515), “aftermarket silencer fitted” (424), “baffles fitted” (377).
What it costs
| Job | Price fitted | Notes |
|---|---|---|
| Rear silencer, standard replacement | £90–£220 | Only if the original box has failed inside |
For an aftermarket system the cost of clearing the advisory is refitting the baffle, or the standard back box if you kept it. For an original system that has gone loud, a replacement rear silencer is the usual fix. Prices by model are on the exhaust replacement cost page.
Can I still drive with this advisory?
If the noise is new and the system is original, get it looked at, because a silencer that has broken up inside can shed pieces that block the pipe. If the noise was bought, the only question is whether you want to keep it.
Enter your reg to see every advisory on your car’s record. Noisy one year and leaking the next means the system, not the owner, is the cause.
Which cars get this advisory most?
The all-vehicle rate is 2.1 per 1,000 tests. The models below are the ones whose owners most often fit a louder exhaust.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Ford Mustang | 5 | 2.2× | 110,849 |
| Mazda MX-5 | 3 | 1.5× | 962,840 |
| Honda Civic | 2 | 1.1× | 3,259,563 |
| MINI (all models) | 2 | 1.0× | 3,449,907 |
| Volkswagen Scirocco | 2 | 0.8× | 497,694 |
| SEAT Leon | 2 | 0.8× | 1,715,594 |
| Ford Fiesta | 2 | 0.8× | 15,017,429 |
| SEAT Ibiza | 2 | 0.7× | 2,030,031 |
| Peugeot 206 | 1 | 0.7× | 1,061,894 |
| Fiat Punto | 1 | 0.7× | 1,031,944 |
Model families are grouped by the first word of the DVSA model name, so “Transit” covers every Transit variant. Only models with at least 60,000 tests are ranked.
This is a list of cars people modify. The Ford Mustang leads at 2.2 times the average, then the Mazda MX-5, Honda Civic, Volkswagen Scirocco and the hot versions of the MINI (all models), SEAT Leon, Ford Fiesta and SEAT Ibiza. The spread is narrow because the advisory is about the owner, not the car.
Motorcycles, which are tested to the same wording and where aftermarket end cans are common, are not shown in this table.
What to do next
- Decide which kind of noisy you have. Chosen, or happened. If the system is original and has got louder, treat it as a leak in progress.
- Fit the baffle for the test. If your system has one. It is the difference between this note and a failure on a strict day.
- Keep the standard system. If you have swapped to a sports exhaust, the original box in the garage is your insurance against a fail, and adds value when you sell.
- Do not confuse it with a leak. A leak has a rasp or a tick, smells at idle, and gets worse. A sports exhaust is simply loud.
Exhaust noisy advisory FAQ
What does exhaust noisy mean on an MOT?
The tester judged the exhaust louder than the standard system for the vehicle but not excessively loud. It is an advisory and the car passes. It is most often written on cars with an aftermarket exhaust or a silencer with the baffle removed.
Is there a decibel limit for the MOT?
No. The tester compares the noise with a standard system for that vehicle and judges whether it is excessive. There is no meter and no number.
Will a noisy exhaust fail the next MOT?
Very rarely. According to DVSA MOT data analysed by PriceMyRepair, 0.9% of 382,681 such advisories failed on exhaust noise at the next test, and 39.7% were advised again.
Can I pass the MOT with an aftermarket exhaust?
Yes, if it is not excessively noisy and the catalytic converter and emissions are unaffected. Fitting the removable baffle for the test is the usual way to stay on the right side of the judgement.
What if my exhaust is original and has become loud?
Then a silencer has broken up inside or a flexible section has split. That gets worse and usually turns into an exhaust leak advisory or failure. A replacement rear silencer costs £90–£220 fitted. These are estimates and final quotes come from garages.
Which cars get this advisory most?
Cars that get modified. The Ford Mustang, Mazda MX-5 and Honda Civic lead, at around one and a half to two times the average rate.
How these figures were calculated. According to DVSA MOT data analysed by PriceMyRepair, from the DVSA anonymised MOT test results (Open Government Licence v3.0): 350,943,111 tests. This advisory was recorded 743,154 times; 382,681 of those were followed to the same vehicle’s next test between 180 and 730 days later. “Fails on the same part” means a failure at that next test under the same defect code and naming the same component, on either side of the vehicle. Testers do not always name a component the same way twice, so the figure is a floor. Method and how to cite.