Engine Management light - second/rear Lambda?

This morning i was drivinng to work and the light came on, so nipped to local fairly friendly place ( charged me a tenner to read fault code and give me 500ml of oil)

and he said it was a error code from the rear lambda sensor, behind the cat?

I know when i last had a service i think the wires to it had been touching exhaust or something and were a bit scorched, but still working ok?

he reset it and i drove back about 10 minute trip and it hasnt come back on. I do know my exhaust is blowing a bit, i was just trying to think of a good excuse to spend more money on a blueflame exhaust instead of £115 on oem one. Not sure she'll buy the lifetime warranty on being Stainless Steel as this oem one lasted 10 years lol

Do you think the exhaust blowing - not very badly, but you can just hear it. would cause this error or is the lambda sensor going too?

if i get new back box is this reachable to be cleaned or anything?

Allan