Mercedes S Klasse Diesel AUC Sensor Issue

That's a weird one. I had a similar issue with my S Klasse. The air conditioning would randomly cut out, and it ended up being a faulty connection to one of the sensors in the HVAC system. Have you checked the connector itself for any corrosion or damage? Sometimes a little bit of electrical contact cleaner can work wonders. Also, double-check the wiring harness to make sure nothing is frayed or broken. If the signal isn't getting through, the blower motor will obviously not work. What error codes are you seeing exactly?

I gave the connector a quick look, but I didn't use any electrical contact cleaner. I'm getting a generic AUC sensor fault. Where exactly was the faulty connection on your car? Was it near the sensor itself, or somewhere else in the system? Any specific wires I should be paying close attention to? Is there a specific type of electrical contact cleaner you recommend?

Mine was right at the sensor plug itself. The pins looked fine at first glance, but they were slightly corroded. A blast of electrical contact cleaner and a small brush sorted it out. In terms of brand, I just used whatever I had lying around, nothing fancy. Given your generic error code and the fact that your blower motor isn't working, it definitely points to a connection issue. Honestly, chasing down electrical gremlins can be a pain. If cleaning the connections doesn't fix it, I'd recommend taking it to a reputable independent workshop. It could save you a lot of time and frustration.

You were spot on. I cleaned the connector with electrical contact cleaner like you suggested, and the blower motor is back in business! The cable or plug connection was indeed defective. The repair cost was around 95€ for the cleaner and my time. Thanks for the help!