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
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