Exhaust failures usually come down to three things: it leaks, it's hanging off, or it's too loud. All three are straightforward to confirm, which makes this one of the easier categories to understand.
Exhaust failures usually come down to three things: it leaks, it's hanging off, or it's too loud. All three are straightforward to confirm, which makes this one of the easier categories to understand.
What's less obvious is where the leak is. A blow at a joint behind the manifold sounds identical from the driver's seat to a blow at the back box, and one of those is a five-minute clamp job while the other can mean dropping the front pipe.
This section covers the exhaust wording you're most likely to see and how the repair usually shakes out.
Exhaust has a major leak of exhaust gases
Gas is escaping from somewhere other than the tailpipe. As well as being noisy, a leak ahead of the sensors can upset the fuelling, and a leak under the floor can let fumes into the cabin.
Full explanation of Exhaust has a major leak of exhaust gases
Exhaust insecure or a mounting is missing
The system isn't properly supported. A missing or perished rubber mount lets the exhaust hang and swing, which then knocks against the underside and puts strain on the joints further forward.
Full explanation of Exhaust insecure or a mounting is missing
Diesel particulate filter missing or has been obviously modified
The tester has found that the DPF fitted when the car was built is gone, or that the casing has been cut open and welded back up. Since 2014 this is an automatic MOT failure on any diesel that left the factory with one — it isn't a judgement call and there's no way around it.
Full explanation of Diesel particulate filter missing or has been obviously modified
How exhaust defects are graded
Every MOT defect is recorded as dangerous, major or minor. Dangerous and major both fail the test; the difference is that a dangerous defect means the car is not roadworthy and must not be driven away. A minor defect passes but is recorded on the certificate, and an advisory is a note that something is wearing and will need attention before the next test. Tester notes in the exhaust section use standard DVSA wording, which is why the phrasing on your certificate looks nothing like plain English — the pages above translate it.
Getting a exhaust failure put right
You are free to take the car anywhere for the repair — there is no obligation to have the testing station do the work, and getting a second opinion on a big quote is sensible. Ask for the failed item to be shown to you on the ramp; a genuine defect is always something a mechanic can point at. Once repaired, a partial retest within ten working days covers the listed items without paying a second full test fee.
Avoiding it next year
Most exhaust failures are found on a pre-MOT check for a fraction of the cost of a failure plus retest, because they are inspected before the clock is running. An MOT at Bob's Mechanical Repairs in Birnam, Dunkeld is £54.85, and anything found is explained and priced before work is agreed. Bob has 32 years on the tools, so the advice you get is what he would do with his own car.
Common questions
Can I drive away after a exhaust MOT failure? Only if the old certificate is still valid and the defect is not dangerous. A defect recorded as dangerous means the car must not be driven on the road until it is repaired, and driving it can mean a fine and points.
Do I pay again for the retest? If the car is left at the testing station and the repair is done there, the partial retest is usually free. If you take it away and bring it back within ten working days, a partial retest is free for the listed items; after that a full test fee applies.
What does an advisory in this section mean? An advisory is a pass with a warning: the item is not bad enough to fail today but is wearing. Advisories on the same item two years running are the ones worth acting on before they become failures.
Decode your exact MOT wording or browse all MOT failure categories.