Car MOT Manual 2012 onwards
Exhaust, Fuel and Emissions - 7.1 Exhaust Fuel and Emissions
A durable repair to an exhaust system which effectively prevents leaks is acceptable providing the system is structurally sound.
A minor exhaust leak from, for example, a connection joint or a pin hole, is not a Reason for Rejection.
2. With the engine running, check the exhaust system for leaks.
3. On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter.
4. During all parts of the emissions test relevant for the vehicle, assess subjectively the effectiveness of the silencer in reducing exhaust noise.
Note: For vehicles not subject to an emissions test, the engine should be revved to around 2500rpm or approximately half maximum engine speed if this is lower.
5. On Class 5 vehicles only, check that the exhaust tailpipe is positioned so it is unlikely that fumes will enter the drivers or passenger area.
2. A major leak of exhaust gases from any part of the system.
3. A catalytic converter missing where one was fitted as standard
4. A silencer in such condition, or of such a type, that the noise emitted from the vehicle is clearly unreasonably above the level expected from a similar vehicle with a standard silencer in average condition.
5. An exhaust tailpipe positioned so that fumes are likely to enter the drivers or passenger area.