A4 B5 with S4 B7 engine: Fan spins much too fast

Good day.

I have an A4 B5 with an S4 B7 engine, and it's running fine overall, except for three communication errors in the engine control unit (ECU). These errors are:

18044 - Data bus driver.
P1636 - 008 - Missing message from airbag control unit.
18043 - Data bus driver.
P1635 - 008 - Missing message from the climate control module.
18058 - Data bus driver.
P1650 - 008 - Missing message from the instrument cluster.

The biggest problem seems to be the issue with the air conditioning. The fans are running at around 70% even when the engine is cold, which is very annoying. In measurement block 125 of the engine control unit, it's also apparent that the air conditioning system is not communicating with the engine. I strongly suspect that's why the fans are spinning up.

I've already tried a few things. The A4 is a facelift model, but from the year 1999, which means the CAN bus system wasn't fully implemented yet, at least not in the climate control and airbag systems, as the corresponding cables aren't present. I tried connecting the CAN lines for the climate control, but it didn't work. Tried plugging in a B7 speedometer, but it still doesn't work.

Since the climate control system is going to be removed, or at least only the control panel for the fan will remain, and a cooling function is not desired, I'm wondering if there's a way to simulate the climate control system (and possibly the airbag) so that the error messages disappear. It's questionable whether the fan will then work normally, but I'm hoping it will. Can anyone help me with this?

Best regards,
Sascha.

The common issue is that it's not specified which specific messages are being missed.

You could log the bus data on the relevant vehicles and then, as a test, send individual IDs from your vehicle.

Best regards, Rainer.