I have a 2001 Audi S4, bought it last week, now my oil temp gauge randomly goes way down then all the sudden will go all the way to the redline, then back down. Also, the gas gauge is fluxuating a lot too. The other day I had half a tank in it, and when I started it later that day, it beeped at me and said I had only 10 miles left on the tank, so I went to fill it up just in case, and I could only put 8 gallons in it. We have checked the instrument cluster, and also hooked up a different one to it, and it still did the same thing. There are no DTCs either. Any clues?! Thanks!!

 

check the power output from the alternator to the battery

 

The oil temp issue is probably failed oil level sensor. Also where the temp signal comes from. Not common but ive seen it before. Also check the wiring thou. As for the fuel level it is probably a sender. After time they get bad spots in the resistor. So itll read fine then itll think theres no gas and then itll start reading ok again.

 

Sounds like you have access to the audi obd software and a hook up cable. Did you reset the readings? May come right back but it is a cheap try. Good Luck!