So recently i did a head gasket change and series of other work on my 08 mini cooper. After re-assembling i started to get error code p0036, heater bank 1 sensor 2 error. It wasn't always on, i could go a week without getting it, sometimes 5 minutes. Logically i replaced the post cat O2 sensor as this was the one throwing the code but within an hour or so of driving i got the same error code. I assumed it may be fuse related but i checked the fuse and there's no visible issues. I didn't replace the pre-cat sensor as it had been done less than 20k ago and it wasn't getting any errors relating to it. The only other thing i can think is its a grounding issue but i don't exactly know where its grounding at. Im going to try and find the ground and clean it off and see if its an issue there but i doubt it. In the mean time if anyone else has experienced anything similar or has any other suggestions it would be greatly appreciated. Thanks!