Hi all. 2010 S4 B8 here. I get a long beep when putting the car into reverse, which, if I'm correct, signals a fault in the sensors?

The reverse lights turn on, so the reverse switch is working.
There is no 'buzz' or 'clicking' from any of the sensors when in reverse.

I've heard that if one sensor is fault it just stops all of them from being used?

What's the best way to diagnose the fault sensor? OBD? Rear bumper off and test each sensor with a multimeter?

Thanks in advance.

Welcome Toby,

A forum search will come up with the information you need, but yes, one at fault and none of them work. Long bleep indicates fault. 
It’s identifying which one is question. 
Some have claimed all except the faulty one will make some noise - never found that myself. Squirting WD40 - no good. 
Diagnostics will identify the offender. 
You then have a choice of paying VAG north of £120 per sensor, or about £20 ish for an EBay one which is likely to have the VAG number imprinted on it. No brainier? 
Um, my experience - EBay one works fine during long periods of dry weather, but fails in damp or rain. So….

Regards,

Gareth. 

Was this information of any help to you Toby?

Yet another Post & Run time waster! 

 @Magnet could you clarify if you would need a garage scan (VCDS) to identify the faulty sensor or would a OBD2 scanner be enough? Thanks

Edited February 3Feb 3 by Tobias123

Welcome Toby and thanks for joining.

Not sure if OBD2 would - but possibly. Mine was identified with VCDS by a small provincial Audi specialist. 
I bought an EBay replacement sensor, marked with the VAG part no. Looked great, and worked for a while before deciding it doesn’t like Welsh rain! OK it was <£20 as opposed to Audi’s £120 +but….?

Does anyone have any good reviews on aftermarket reverse sensors?

Regards,

Gareth. 

Ok I might take mine to a garage then. Tricky decision regarding the sensors…I’ve seen the ones on EBay - tempting. But I guess I’ll have to make that decision after going to the garage. Will come back and let you know the results…no idea when though! Thanks Gareth