Solved - Strange parking sensor problem

bladeowner

bladeowner

Senior member
 Yorkshireman in High Wycombe
Hi, My parking sensors have stopped working properly when the engine is running. Although sometimes the gong squawks a little like it's trying to beep. When I just turn on the ignition but not start the car they work fine. Each sensor is 'ticking' whether the engine is running or not and works perfectly with an obstacle - if I don't start the car. I have tried another gong and it's just the same. Any ideas anybody? I'm baffled. :?
 
Weird. If you think about the difference, the only thing is that the alternator is running. Do you get interference on the radio? I'm wondering if a suppressor is failing and you're getting interference on the 12v line.

The battery heading towards end of life can cause all manner of strange things, but this doesn't sound like that type of symptom
 
Hi, No there doesn't appear to be any interference on the radio. I have an oscilloscope but no probe at the moment and so I could check when I get one. I am thinking that maybe the PDC controller also gets a signal to say the engine is running?? - and this is a bad connection. As I mentioned, it seems like it tries to work. The reversing light comes on in both scenarios. Is the same switch used for PDC and the reversing light? Thanks.
 
bladeowner said:
Hi, No there doesn't appear to be any interference on the radio. I have an oscilloscope but no probe at the moment and so I could check when I get one. I am thinking that maybe the PDC controller also gets a signal to say the engine is running?? - and this is a bad connection. As I mentioned, it seems like it tries to work. The reversing light comes on in both scenarios. Is the same switch used for PDC and the reversing light? Thanks.
Click to expand...

That I don't know, but I'd suggest a dirty switch would give you the same symptom whether or not the engine is running.

I'd probably test the battery (as that's a simple thing to do if you have a meter) and then check the 12v line. You could also check for noise on the earth when the engine is running as that would also bugger up the voltages.

After that it's probably worth plugging into diagnostics for any errors. If you've got iffy voltages flying around there's a good chance something else will get upset.

Another giveaway is the rev counter "bouncing" randomly (the needle randomly skips up and immediately back to a correct reading with no change in revs)

You have an oscilloscope! Good man :thumbsup:
 
I checked the 12v to the gong and the voltage is pulsing when the engine is running. Other 12 V lines are fine as far as I can tell. I left the scope on it and started pulling fuses to see if another unit was causing it. When I pulled fuse 23 the pulsing stopped. F23 is a 5A fuse for various lighting circuits. The PDC worked ok then for a few seconds but the dashboard warning lights don't work with the fuse pulled and so this stopped it.
Obviously the gong doesn't like this pulsed DC and so for the interim I've soldered a 220uf capacitor inside the gong across the supply rail to smooth the dc- all now working.
So I still need to find out why this rail is pulsing. Anybody know a link for decent wiring drawings of the car?
 
bladeowner said:
I checked the 12v to the gong and the voltage is pulsing when the engine is running. Other 12 V lines are fine as far as I can tell. I left the scope on it and started pulling fuses to see if another unit was causing it. When I pulled fuse 23 the pulsing stopped. F23 is a 5A fuse for various lighting circuits. The PDC worked ok then for a few seconds but the dashboard warning lights don't work with the fuse pulled and so this stopped it.
Obviously the gong doesn't like this pulsed DC and so for the interim I've soldered a 220uf capacitor inside the gong across the supply rail to smooth the dc- all now working.
So I still need to find out why this rail is pulsing. Anybody know a link for decent wiring drawings of the car?
Click to expand...

Have you replaced any bulbs with LED's?

Mike
 
Ducklakeview said:
bladeowner said:
I checked the 12v to the gong and the voltage is pulsing when the engine is running. Other 12 V lines are fine as far as I can tell. I left the scope on it and started pulling fuses to see if another unit was causing it. When I pulled fuse 23 the pulsing stopped. F23 is a 5A fuse for various lighting circuits. The PDC worked ok then for a few seconds but the dashboard warning lights don't work with the fuse pulled and so this stopped it.
Obviously the gong doesn't like this pulsed DC and so for the interim I've soldered a 220uf capacitor inside the gong across the supply rail to smooth the dc- all now working.
So I still need to find out why this rail is pulsing. Anybody know a link for decent wiring drawings of the car?
Click to expand...

Have you replaced any bulbs with LED's?

Mike
Click to expand...

I did wonder about that myself but only fitted a few leds after the problem started. Anyway, the only leds that are lit are the sidelights as drl and they are on when the ignition is on but engine not running as well and it doesn't cause an issue then.
I ran the engine with alternator disconnected and the problem stopped and so it does appear to be the alternator.
 
bladeowner said:
Ducklakeview said:
bladeowner said:
I checked the 12v to the gong and the voltage is pulsing when the engine is running. Other 12 V lines are fine as far as I can tell. I left the scope on it and started pulling fuses to see if another unit was causing it. When I pulled fuse 23 the pulsing stopped. F23 is a 5A fuse for various lighting circuits. The PDC worked ok then for a few seconds but the dashboard warning lights don't work with the fuse pulled and so this stopped it.
Obviously the gong doesn't like this pulsed DC and so for the interim I've soldered a 220uf capacitor inside the gong across the supply rail to smooth the dc- all now working.
So I still need to find out why this rail is pulsing. Anybody know a link for decent wiring drawings of the car?
Click to expand...

Have you replaced any bulbs with LED's?

Mike
Click to expand...

I did wonder about that myself but only fitted a few leds after the problem started. Anyway, the only leds that are lit are the sidelights as drl and they are on when the ignition is on but engine not running as well and it doesn't cause an issue then.
I ran the engine with alternator disconnected and the problem stopped and so it does appear to be the alternator.
Click to expand...

Ok - I'll let you know when I've changed the rectifier and post before and after scope traces.

Mike
 
OK, after over 5 years I've actually cured this problem instead of a sticking plaster remedy. It turned out to be an internal fault in the GM5 module. I discovered a similar problem reported on M3Cutters from 2011 and so I'd been looking for a second hand GM5 module at a reasonable price for a couple of months as they are more expensive than similar but not usable E46 modules.

As soon as I connected the 'new' module I checked to see that the PDC was working properly again - which it was. Then you have to use SSS/Progman to initialise/program it to the car, then I re synced the keys to the car as the keys won't open the doors remotely with the different module, then I recoded the module with my preferences with Carly.

My main problem was with SSS/Progman as there is a bug in my version that doesn't read the battery voltage with a non standard diag head. The software requires the battery level to be above 13V before it will program. Luckily I had another version which seems to be hacked to fool the software.

Result :D Eventually.
 
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