I have checked the exhaust and the only thing I could find was maybe the slightest of leaks at the joint between the cat and the cat back system. I couldn't even feel it blowing. I even held a piece of tissue by the suspect area and it wasn't blowing that or even changing the colour of it. The only signs of a leak was a black mark on part of the joint. Therefore, Along with the fact that it is post cat, I don't think this would cause the fault. Remember, the fault I have is with the pre cat sensor in the downpipe.
I also checked the sensor cabling and plug for any signs of damage, and it all looked like new.