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Discussion Starter #1
Since I receive such a great answer to my last problem, here's the one other thing I'm facing (other than a CPS):

My Front PDC goes into an on-off cycle mode when I get close to an object. Away from an object, everything is fine. As I get close, I get a slow beep, then a bit faster, then...the system shuts off, the beeps stop, the light on the switch goes out... then it comes back on and beeps with increasing frequency as I get closer to the object then...it shuts off again.

The cycle repeats itself, about 3-4 seconds on and 3-4 seconds off.


Don't know if it's related, but the rear PDC is also acting up. I hear a very, very faint beeping, which acts as it's supposed to. The diagnostics say there is a gong error, so I assume the front and back beeps are generated from a different component, and the rear one is just bad. I don't know if that might be causing the front problem also.

Thanks for any help.

(yes, I did search, but I didn't uncover the radio answer searching either, so my search skills must need some work...)
 

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PDC consists of 12 different components:
4 sensors in the front bumper
4 sensors in the rear bumper
a front gong
a rear gong
a control unit
on/off switch on the dash

The sensors are all wired in series - if one goes bad then the system is supposed to flash the PDC light on & off as soon as it is engaged.

If your rear PDC if faint, then your rear gong is probably dying.

If your front PDC is cycling, then you either have a bad control unit or you have a bad sensor.

Checking the sensors is easy. Turn on PDC using the dash button. Get out and walk to the first sensor. Stick your ear in front of it. If you hear a faint ticking noise, that sensor is ok. No noise = bad sensor.

Hope this helps!

d-
 

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Discussion Starter #3 (Edited)
I'm fairly confident the sensors are working. I was in the shop when my SA had the GT1 software running and saw the sensor signal go from 0 to 100 for each of the 8 sensors as his assistant walked toward each one.

There is a stored code for the gong, so it sounds pretty certain that explains the rear. In front, if each sensor is getting a signal to the ODB2 port, I would think the sensor and wiring would have to be working. Perhaps a bad control unit.

Playing with it this evening:

When a sensor is first in range, it beeps slowly about 15 times, then cycles. As I get closer and it beeps faster, it beeps about 6 times, then cycles. Closer, two beeps and cycle, and right on top of the obstruction, one quick beep and cycle. The closer I am to the object, the faster it happens.

I'll post what's found later in case anyone sees these symptoms in the future.
 

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My rear pdc has never worked consistantly, but the other day when me and a friend took out the rear trim to get to the top of the suspension and then put everything back together my pdc now works all the time.
 

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Your SA couldn't diagnose the problem?

Anyway, the PDC control module cycles through the various sensors, they are not all on at the same time (1-2-3-4, repeat). When an item is detected in any given sensors range the PDC cycles through that sensor more frequently (1-2-3-2-4-2 for sensor 2) with the frequency increasing the closer you get.

I would suggest you perform a test on each individual sensor to see if the system still resets - you may just have a bad sensor that can't cycle as quickly as the system would like.

If all sensors are fine I would go ahead and replace the gong then the control module.

d-
 

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Discussion Starter #6
Sounds like a logical approach I can try myself.

To be fair, there was an unexpected brake job added to the state inspection and radio/pdc issues, so he ran out of time and I'm going back next week to fix.
 

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Discussion Starter #7
Can someone do me a favor and check something?

When you key is out of the ignition, can you still turn the PDC on, with it beeping as you walk around the car?

I was demonstrating what I had found earlier today, now my service guy called and said the car is acting oddly, doing the above. He's thinking there's an ignition switch problem and wants to go hunting down wiring problems.

First he's going to check a X5 with PDC to see if it does the same thing. It doesn't seem logical to have PDC active when the car is off, but I don't want to spend money chasing down a problem that doesn't exist.

Thanks
 

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Can someone do me a favor and check something?

When you key is out of the ignition, can you still turn the PDC on, with it beeping as you walk around the car?

I was demonstrating what I had found earlier today, now my service guy called and said the car is acting oddly, doing the above. He's thinking there's an ignition switch problem and wants to go hunting down wiring problems.

First he's going to check a X5 with PDC to see if it does the same thing. It doesn't seem logical to have PDC active when the car is off, but I don't want to spend money chasing down a problem that doesn't exist.

Thanks
When I remove the key (2003), the PDC light goes off ... and, pressing it, with the key removed, doesn't turn it on ... nor does it activate the sensors. They are totally quiet. (2002 "may" be different, but I doubt it. It would eventually drain the battery ... i.e., parking close to an object with the PDC ON.)

You have a problem.
 

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Discussion Starter #10 (Edited)
Checking in for an update and a question.

I brought the car to my dealer and asked to replace the rear gong. First, they wouldn't do anything without a $90 diagnostic. Then they told me it was a front sensor. My front sensors work fine, but they swore that was the problem, so another couple hundred dollars to replace. The update call - we replaced the front and don't get the same error code, but now you have a bad rear gong... Grrr.

Having to pick the car back up, and not a lot of spare time, I didn't get the car back to the shop for a few months. OK, time to replace the rear gong. Not so fast my friend - our diagnosis says it's a bad control unit. Ummm...why did you diagnose it differently last time. Umm... And what happens when you replace the control unit and you come back and tell me it's a bad rear gong? Oh, we're sure it's a bad control unit. Next day...we replaced the unit, and the error code is gone, but now we've determined that you have a bad rear gong... Grrr^3.

So I've had 3-4 "diagnoses" and 2 repairs that fixed nothing, and absolutely nothing to touch the simple component that is broken. Do repair shops no longer do what you ask them to do?

Anyway... anyone have guidance on replacing the rear gong myself? The online parts drawings that I found don't even list a rear gong for the rear PDC system (it's there on various M3 schematics, but not the E39 M5). (RealOEM.com BMW E39 M5 Park Distance Control (PDC))
 

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Checking in for an update and a question.

I brought the car to my dealer and asked to replace the rear gong. First, they wouldn't do anything without a $90 diagnostic. Then they told me it was a front sensor. My front sensors work fine, but they swore that was the problem, so another couple hundred dollars to replace. The update call - we replaced the front and don't get the same error code, but now you have a bad rear gong... Grrr.

Having to pick the car back up, and not a lot of spare time, I didn't get the car back to the shop for a few months. OK, time to replace the rear gong. Not so fast my friend - our diagnosis says it's a bad control unit. Ummm...why did you diagnose it differently last time. Umm... And what happens when you replace the control unit and you come back and tell me it's a bad rear gong? Oh, we're sure it's a bad control unit. Next day...we replaced the unit, and the error code is gone, but now we've determined that you have a bad rear gong... Grrr^3.

So I've had 3-4 "diagnoses" and 2 repairs that fixed nothing, and absolutely nothing to touch the simple component that is broken. Do repair shops no longer do what you ask them to do?

Anyway... anyone have guidance on replacing the rear gong myself? The online parts drawings that I found don't even list a rear gong for the rear PDC system (it's there on various M3 schematics, but not the E39 M5). (RealOEM.com BMW E39 M5 Park Distance Control (PDC))
Part #5: Trigger Contact PDC

It sits on your rear deck next to the 3rd brake light.
 

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Discussion Starter #12
Part #5: Trigger Contact PDC

It sits on your rear deck next to the 3rd brake light.
Thanks. I could have sworn they gave me a P/N with a description that said "gong" in it, but maybe that was just from all of the conversations.

Any info on how to access it - from the trunk or from the rear of the cabin? Perhaps it's obvious once I look, but I'm away for the week.
 

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Thanks. I could have sworn they gave me a P/N with a description that said "gong" in it, but maybe that was just from all of the conversations.

Any info on how to access it - from the trunk or from the rear of the cabin? Perhaps it's obvious once I look, but I'm away for the week.
The "gong" is under the front dash down by your right shin.

The rear speaker is accessed by removing the rear deck. Good time to upgrade your rear speakers / subwoofers, or at least make sure all the bolts are tight, and condition those hard to reach portions of your rear seats as you basically need to remove the rear of the car. As someone once said "BMW places the subwoofers and then builds the car around them"
 
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