From the latest online MOT test manual:-
7.1 Exhaust System 7.1 - page 1
The M.O.T. Inspection Manual Issue Date April 2013
Information Method of Inspection Reason for Rejection
The overall security of the exhaust system
should be assessed; one or more exhaust
mountings missing may not be a Reason for
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
1. Check the security of the exhaust system.
2. With the engine running, check the exhaust
system for leaks.
3. On petrol engine vehicles that qualify for a full
catalyst emissions test, check the presence of
the catalytic converter.
Note: To ascertain whether a vehicle qualifies
for a full catalyst test, use the flow charts in
Section 7.3.C disregarding the result of the
Basic Emissions Test.
4. During all parts of the emissions test relevant
for the vehicle, assess subjectively the
effectiveness of the silencer in reducing exhaust
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 driver’s or passenger
1. An exhaust system not adequately supported.
2. A major leak of exhaust gases from any part of
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
5. An exhaust tailpipe positioned so that fumes
are likely to enter the driver’s or passenger
Section 3 applies.
Once again, a Diesel is subject to a smoke test.
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