Parking Distance Control (PDC) intermittent

[Phillip Biggs]

When I engage reverse gear the PDC will beep erratically whether I’m near anything or not. Kind of ‘beep,,beep,,,,beep,beep,,beep,,,,,beep,beep’ (if that makes sense). When I get quite close to an object it works normally; getting faster until I get a continuous tone. Very occasionally it works without problems.
I had the idea of unplugging one sensor at a time to narrow it down, but then none of them worked. They must be wired in series I suspect, or a safety feature.
I then sat in the boot and covered each one in turn to see if one didn’t work. But each caused a continuous beep.
The car is out of warranty so I’d like to fix it myself if possible. Has anyone seen this behaviour before and if so what fixed it?
Are we talking a single sensor becoming over sensitive, or the control box in the boot, or something else?

[///Matt]

It may sound stupidly simple, but are the sensors clean? If anything else, it is very likely just one sensor is failed...

[Phillip Biggs]

Thanks for your prompt suggestion.
I've read elsewhere that dirty sensors could cause a problem. I've assumed that they would have to filthy dirty to give false echo returns (and I'd have thought that would cause a continuous beep). The car has never been that dirty and has stilll shown the problem after a normal but through wash.
I haven't studied the sensors closely to see if any grit particles are wedged into one of them, but it would have to be very small for me to have missed it.
I'll check tomorrow anyway and brush them with an old toothbrush.

[Phillip Biggs]

Checked the sensors this morning. They were clean, but to be on the safe side I brushed them with a toothbrush. Still have the same problem. You think it more likely an individual sensor than the control box though?

[drz]

^^ Yes, it is more likely that either a sensor is going bad, or that an electrical connection is not making very good contact. The controller should be the sturdiest component of that system.

[Phillip Biggs]

Thanks for that. I'll let you know the outcome.

[Phillip Biggs]

Good news! Fixed it. It was a sensor going bad. I bought a new one (from eBay) and fitted it but later got the beeps again. So I then replaced the next sensor with the one I'd removed earlier and (touch wood) it's been OK since.
By the way, as I work on my car (an E46 02 Compact) I'm recording how I took it apart and then writing it up as a PDF. I've only done a couple so far and will put them up on my website for anyone who's interested.
They'll be on www.imagefair.co.uk/BMW in a week or so. If anyone has thoughts on sites that might list 'how to documents' then let me know.

[Phillip Biggs]

Decided to get on and upload the two PDf's strait away. www.imagefair.co.uk/BMW/BMW.htm
More will follow over time, including the rear bumper one - not that it's that difficult anyway

[Phillip Biggs]

Update. I started having that intermittent beeping I mentioned in my first post again. I ignored it as over winter I didn't want to work on the car. Then it got worse. The first time I put the car in reverse after turning it on I would get one long continuous beep for about 5 seconds then it would go off and I'd never hear another beep from it until I turned the ignition off and on again. I think it's the car telling me that the sensor has failed completely. So I bought another sensor (eBay again - god knows why these things are so expensive) and fitted it. This time because the fault was permanent I was quickly able to work my way along the line of sensors until I got to the faulty one. It turned out to be the forth one I tried of course and as it happens the one I replaced in 2005.

[bobdisk]

Bit late for you now? A way of checking reverse sensors is to pick a quiet place for this ! Turn on ignition but dont start the engine. Put it in reverse, then go and put your ear close to each each sensor in turn. If it is good, you will hear a faint clicking noise. No noise, no good!

[Phillip Biggs]

Thanks for that. I'll remember for next time.