mechanics.trade
Exhaust repair and replacement
The exhaust carries gases away from the engine, quietens them, and cleans them through the catalytic converter and, on diesels, the particulate filter.
What exhaust repair means
It sits under the car in the weather and salt, so the back sections usually go first.
What the job covers
- Back box, centre section and downpipe
- Flexi-pipe and manifold repair
- Lambda sensor replacement
- Exhaust blow diagnosis
- Stainless and performance systems
When you might need it
- The car has got noticeably louder, especially from cold.
- A rattle from underneath, which is often a heat shield or a broken mounting rather than the exhaust itself.
- A smell of fumes inside the car, which should be looked at promptly.
What it costs, and what changes the price
Typically £120 to £600.
- Exhausts are usually replaced in sections, so a back box costs far less than a full system.
- Stainless steel costs more than mild steel and lasts much longer.
- Seized bolts add labour time, which is why a quote may depend on how the job goes.
How long it takes
A back box is often under an hour. A full system takes two to three hours.
What the MOT data shows
Out of 42,728,066 MOT tests in 2025, these are the parts covered by this job that testers recorded as faults.
| Part | Recorded in 2025 |
|---|---|
| Exhaust system | 360,208 |
Common questions
Can a hole be welded rather than replaced?
Often yes, if the surrounding metal is sound. If the section is thin all over, a weld will not hold for long and a new part is the better spend.
Will a blowing exhaust fail the MOT?
Yes. A leak, excessive noise, or a system that is insecure are all failure items.
Is a louder exhaust legal?
A replacement must not be louder than the original system. Aftermarket exhausts sold for road use should be marked as meeting the standard.