AUC and Temp sensors
 

HI im have been getting a Auc sensor error (even after replaceing with oem sensor) error for as long i have woned my E53. today my temp gauge went all the way right pulled over restarted the car and it went to normal. could the two problems be related and how?

The temp "non gauge" situation is a known bug happened to me a couple times in the 77k miles I had my e53.

AUC check the wiring I'm not sure the expected voltage values but you should be able to find the pin out and measure voltage. It's fairly common for a ground to come off in the engine bay so off it's a grounded device I would start there.