Exhaust system:

An excessively deteriorated exhaust system or part of the system missing is a reason for failure.

Obstructions at the tailpipe which prevent the gas analyser probe from being inserted will also result in failure.

Mountings that are missing will also fail. Alternative mountings that are not likely to fail prematurely are acceptable.

Durable repairs to the system are acceptable as are minor leaks from joints or pin holes.

Where an exhaust system fails for major leaks then a further emissions test will be carried out when the vehicle is re-tested. This could mean the vehicle passing the emissions test originally but failing the re-test after the leak has been repaired. Major leaks in the system can reduce the emissions arriving at the tailpipe and give a false reading.

"Loud" systems may fail if they are clearly unreasonably above that expected from a standard system fitted to that model.