Strictly speaking the second O2 sensor is there to verify the functioning of the cat and to disable it in any way could be an MOT failure as it is illegal to interfere with the correct functioning of the anti-polution systems in any way. Since we interfere with it when we fit a sports exhaust I suppose it doesn't matter much if we also circumvent it by disabling the system that checks the correct functioning of the cat. innocent
If the O2 sensor was installed in the system correctly you would probably have a constant warning light and fault and that would be an MOT failure.

Just so you know.

Peter

[Linked Image]