Will my exhaust fail my MOT?

Thursday 30th July 2026

Yes, your exhaust can fail an MOT test if it has a major fault such as a serious leak, doesn’t fit properly, lets fumes into the cabin, is too noisy or fails the  emissions test. Less serious issues, such as early signs of corrosion or a leak that has not yet reached the tailpipe are more likely to appear as an advisory. Our guide explains the common reasons behind an exhaust MOT failure, and what you can do before your MOT to give your vehicle the best chance of passing.

Common reasons an exhaust fails an MOT

There are four common reasons your exhaust may fail an MOT, these include:

• Leaks: A major leak from a corroded or loose exhaust is a fail, as is exhaust fumes entering the cabin. If those fumes pose a danger to health, then that’s treated as a dangerous fault rather than a major one and you will not be able to drive your vehicle until it is repaired and retested.
• Security: The exhaust must be attached securely. A single missing or worn mounting doesn’t automatically fail the exhaust; the tester looks at the overall safety of the system rather than at each component on its own.
• Noise: While there is no fixed decibel limit, the exhaust will fail if its noticeably louder than a similar vehicle with a standard silencer in average condition. The exhaust will also be checked to make sure the noise suppression system is secure. Aftermarket systems are at the biggest risk of failure.
• Emissions: An emissions test is carried out on petrol and diesel cars to ensure emission control equipment is working correctly and that emissions or smoke opacity levels don’t exceed the limits set by the manufacturers, or the default limits.

When might an exhaust pass with an advisory instead?

An advisory means that the tester has spotted a fault that is not serious enough to cause a test fail but is worth keeping an eye on.. For exhausts this usually covers surface corrosion that hasn’t yet reduced the system’s structural integrity or caused  a minor leak or blow.

Corrosion and leaks tend to worsen over time, an advisory this year is likely to develop into a fail next year.

What can you do before your MOT?

There are a few checks you can do to catch most exhaust-related issues while they’re still affordable to fix. Listen out for unusual noises, such as hissing, popping or a loud roaring sound when accelerating. These are the tell-tale noises that indicate your exhaust gases are blowing through a hole or loose joint.

Have a visual check underneath your car to spot holes, black sooty stains around the joints and corrosion around the welds and silencer box. To check your exhaust is properly secured have a look at how low your exhaust hangs, and if it rattles when driving over speed bumps or potholes .

Look back on last year’s test. If you had any advisories last year, get your vehicle checked over instead of waiting to see if it might fail.

Ready for your MOT?

Here at Formula One Autocentres, our qualified engineers can inspect your exhaust as part of a service before your MOT. Book your service and MOT together at your local Formula One Autocentres branch to save. Prices start at just £29.50.