It's pegged at max, when driving, engine off, even when battery is disconnected. No movement at all.
Does this mean the sender or the gauge is faulty?

 

probably one of the connectors on the sender is broken; I mean not connected any more

Marton

 

Second the above post!

 

Well, I'm gonna go a different way. If the meter is pegged, with the batt disconnected, I would say you have at the very least, a gauge problem. So, key off, engine off, meter pegged you need to resolve your gauge problem first, then find out what caused the meter to peg. could be the sender, or depending on year, it could be the wiring harness across the front of the engine. We don't know your model or year, so that's speculation.

Doc

 

Oops, sorry guys, its a 88 S4 Euro.
I'll check the sender tomorrow. If it is, why would this happen? For instance, oil filter change?

 

As Doc Mirror said, gauge problem. I had a similar problem and found that a good whack on the pod released it i.e. the needle was going too far and physically sticking.

The reason for the needle going too high may be gauge, sender, grounds etc but the needle should still return to zero when engine is off. Mine was resolved during an instrument cluster cleanup and by cleaning the wiring at the jumper post under the hood - one of these fixed it, I just don't know which one.

 

The problem I found was two-fold. My sender had an intermittant connection, and when it passed through about 2-ish bar, the needle was pegged. Simple fix, R&R the sender. Next problem, the S4 cars have a large bundle of sensor wires, and the charge line from the ALT to the jumper post runing across the front of the engine. That is a hot area, plus the charge line gets a lot of current and runs hot, plus it's 18 years old, all add up to common insulator faults in the wiring. After checking the sender, then the gauge, you can dig into that harness and see if it's melted like mine was.

Doc

 

Thanks guys, superb advise!!
I'll start with the whacking (never thought I'd whack a Porsche!) and go from there.
You guys are great!
Ken

 

Da whack did it, its down now!
Now to see what caused this...
Thanks again guys!!

 

Problem solved! It was the oil pressure sender after all! I whacked the pod to bring the needle down to zero, replaced the old with the new sender, and I now have a working oil pressure guage thanks to you guys!
Cheers!!
Ken