The MOT Files

MOT defect file

Exhaust mounting deteriorated or missing

Last updated

Quick answer

A rubber hanger or bracket holding the exhaust up has perished, broken or gone altogether. On its own that is not automatically a failure — the tester judges whether the system as a whole is still secure.

Typical cost
£20–£120
DIY viability
Possible with care
Underfloor exhaust layout and emissions-control componentsA side elevation traces exhaust gas from the engine manifold through the catalytic converter, a diesel particulate filter and rear silencer to the tailpipe. A lambda sensor is mounted upstream of the catalyst and rubber hangers support the pipe beneath the floor. The catalyst and DPF are highlighted as required equipment, while one torn mounting is marked as insecure. Removing a fitted catalyst, tampering with a DPF or leaving the system insecure is an MOT failure.Vehicle floor — side elevationManifoldLambda sensorCatalytic converterDPF — must not be removedRear silencerInsecure mountingMissing catalyst · tampered DPF · insecure exhaust = fail
The exact order varies, but the catalyst and any factory-fitted DPF must be present and untampered. The complete system must also be secure. A lambda sensor samples exhaust oxygen so the engine can control fuelling.

What you might notice

  • A rattle or knock from underneath over speed bumps and potholes, often worse cold
  • A drone or buzz at one particular engine speed, as the system sits closer to the floor than it should
  • The tailpipe hanging noticeably low, or no longer central in its cut-out
  • A perished, split or empty rubber hanger visible under the back of the car — this is easy to check yourself with a torch

What causes it

  • Rubber hangers perishing with age and heat cycling, which is simply how they wear out
  • Corrosion of the mounting bracket, or of the welded tab on the exhaust that the rubber hooks onto
  • A heavier aftermarket silencer, or a replacement section fitted slightly out of line, loading the mountings unevenly
  • Speed bump and kerb impacts tearing a hanger, or stretching one until the system sags onto the heat shield

Advisory or failure?

The tester assesses the overall security of the exhaust system rather than counting mountings, and the manual is explicit that one or more missing or defective mountings does not necessarily make the exhaust insecure. So a perished hanger on a system that is still properly supported is usually recorded as an advisory. It becomes a major defect where the system as a whole is insecure, or where the movement has opened a joint and the exhaust now has a major leak. Where any part of the noise suppression system is likely to become detached, the grading is dangerous. Two related items are graded separately and more harshly: exhaust fumes entering the cabin is a major defect and becomes dangerous where they present a danger to the health of people on board, and exhaust noise unreasonably above what you would expect from a similar car with a standard silencer in average condition is a major defect. If a mounting has failed, expect the tester to look closely at the joints either side of it.

Can you fix it yourself?

Possible with care

This is one of the more achievable jobs under a car. Rubber hangers cost a few pounds, and the usual technique is a smear of washing-up liquid and a pry bar or a purpose-made hook tool to stretch the new one over its pegs. Work on axle stands rather than a jack, and let the exhaust cool properly first — it stays hot for a long time and it is directly above you. The traps are the ones you find rather than the ones you expect: a bracket that crumbles when the old rubber comes off is a welding job, and a system that has been hanging low for a while has usually been stressing a joint, so check for a blow at the same time. Cable ties and coat hanger wire are not a repair and a tester will treat them accordingly.

What it costs

A rubber hanger is £3 to £12 and takes minutes, so doing it yourself is nominal and a garage will typically charge £20 to £50 including the part. The cost rises when a bracket has to be fabricated or welded back on, which is £60 to £120, and when the movement has already damaged a joint or a flexible section — at that point you are paying for a section of exhaust rather than a rubber. Replacing all the hangers at once while the car is on the ramp is worth doing, since they age together and the parts cost almost nothing next to the labour of going back under.

What happens if you ignore it

A system left swinging on one fewer mounting than it should have works the joints and the flexible section until something cracks, and a small blow then becomes a section replacement. Where a leak develops ahead of the passenger compartment, carbon monoxide can be drawn into the cabin, and it gives no warning before it makes you drowsy. Worst case, a section eventually parts company and drops onto the road, which is a hazard for whoever is behind you and can catch and damage the underside of your own car on the way down.

Common questions

Is a broken exhaust mounting an MOT failure?
Not automatically. The tester judges the security of the system as a whole, and the manual is explicit that one or more missing or defective mountings does not necessarily make the exhaust insecure, so a perished hanger on a system that is still properly supported is usually an advisory. It becomes a major defect where the system is insecure or the movement has opened a joint into a major leak, and dangerous where part of it is likely to become detached.
Can I hold my exhaust up with a cable tie?
No. Cable ties and coat hanger wire are not a repair and a tester will treat them accordingly. The correct rubber hanger costs a few pounds, and anything improvised lets the system move enough to keep working the joints and the flexible section until one of them cracks, which turns a small job into a section of exhaust.
Can I replace an exhaust rubber hanger myself?
Yes, this is one of the more achievable jobs under a car. A smear of washing-up liquid and a pry bar or a purpose-made hook tool will stretch the new rubber over its pegs. Work on axle stands rather than a jack and let the exhaust cool properly first, because it stays hot for a long time and it is directly above you.
How much does an exhaust mounting cost to replace?
A rubber hanger is £3 to £12 and takes minutes, so a garage will typically charge £20 to £50 including the part. Fabricating or welding a corroded bracket back on is £60 to £120. If the movement has already damaged a joint or the flexible section you are paying for a length of exhaust instead. Replace all the hangers while the car is up.
Is a loud or blowing exhaust an MOT failure?
Yes, where the noise is unreasonably above what you would expect from a similar car with a standard silencer in average condition, that is a major defect. Exhaust fumes entering the cabin is also a major defect, and becomes dangerous where they present a danger to the health of people on board, because carbon monoxide gives no warning before it makes you drowsy.

Fault codes behind this failure

A failure certificate records that the lamp was lit, not what lit it. If this is what your certificate says, one of these codes is usually stored behind it, and reading it is the difference between a diagnosis and a guess.

This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.

Has this been recorded on your car?

Check the full MOT history for any UK registration.

Spaces are optional

Other common defects