Audi A6 C7 CGQB – the heating has stopped working. The car has a diesel auxiliary (parking) heater, which would start automatically every time the car was started in cold weather. What happened is this: in the morning I started the car, the heater also started, and it began blowing warm air. After driving about 10 km, the heating disappeared, the heater failed, and there are active fault codes in the engine and climate control modules: U111100.

The car is at a service center, but they can’t find anything. It only blows cold air. Diagnostics cannot connect to the parking heater.

What could have happened? Wiring issue? Control module failed? Please help.

That fault code and the fact they can’t connect to the module would mean a loss of 12v feed or earth or complete-module failure, canbus wiring fault seems unlikely as would expect to see communication missing faults in other modules. 

 

I would hope they have tested the module for a power and earth feed on the plug. Canbus can be checked for resistance or with a oscilloscope and all being good it points module having failed 

 

Looks like I’ll probably have to take the car to another service 😁 But why is there no heating ? Does it fail to start the auxiliary circulation pump? Or is the problem elsewhere? Both hoses going to the heater matrix are cold.