I've been going through all the threads that dealt with this, and a few days ago I found one the gave a thorough testing procedure for the module, with what voltages to look for on what pin. I thought I had saved the link but apparently did not. I've just spent over an hour going through the threads with variations on parking assist, backup alarm, reverse alarm etc, and still haven't found it. Does anyone recall that thread and who the author was? There is a sticky that talks about the problem but doesn't have the detailed diagnostic procedure like the one I found. In my case all my sensors are silent and I get the 3 second warning alert when I go into reverse.

Hopefully someone knows which thread I'm talking about. There are an awful lot on the subject.

 

Vehicle info?

 

It's on my sig line but 2001 s-type 3.0

 

You did - my bad (that's what I get for replying to posts via mobile app)

 

OK, here is what I would do...

1) Check the harness going to the park assist module. (on rear of trunk - lower left side - for US models) I believe right side for non-US models. Disconnect harness (flip up connector) and make sure both the harness and module (held by 2 bolts) is clean, free of water and no rust on any connectors.

2) Two outside parking sensors only. (Jack up rear of car - secure) and check connections to both rear outer sensors - have a good flashlight and it's a lot of feeling your way around. (It could be a loose connector) Make sure connector is fully seated. Use di-electric grease before re-fitting connector or you might have a hard time getting the connector to fully re-seat in the parking sensor.

3) Remove both outside sensors - two tabs hold the sensor to the bumper and comes out from the inside of the bumper (and clean w/ QD electronic cleaner)

4) If the three items above doesn't resolve your issue - you have to drop the rear bumper to get to the two inside parking sensors. Same deal - check connector and ensure the connector is fully seated.

Each sensor has holes in them and they get "blocked" with road dirt, etc - again, happens more with the outside sensors then the inner ones.

Hopefully it will be an easy find and fix.

 

Well, having a good look at the schematic I decide to plow ahead on my own, although I didn't have a great deal of hope. First of all, the symptoms were the 3 second alarm, the red LED coming on in the overhead switch, and outside, no clicking or wheezing or chirping from any of the sensors with the ignition on and car in reverse.

I assume that all 4 sensors being addled is unlikely so it was someting with the module. The backup lights were coming on and I checked that wire to the module and it showed a ground, as it should. I had 12V to the module and a good ground. Given the the speaker was working, the self diagnosis was working, the overhead switch was working, all it pretty much left was the module. I pulled it out and found evidence of some minor water damage. I pulled the circuit board and there was slight corrosion on a few of the copper lands but I checked those, and they still gave continuity. I plugged it back in outside of the case and nothing got hot on the board while power was on. I followed the wire harness from the module back to the main harness, and didn't see any problems.

At this point, all I can see is the module being fragged. It appears to be getting the correct inputs, but with no outputs, except alarm. I'm always suspicious of blaming electronics as they are usually the most reliable part of the whole circuit, but don't know where else to look at this point.

 

Feel free to utilize the other "tips" I outlined beyond the module before replacing it. You can always go to a dealership and they can obtain the code(s) to tell you what is preventing the parking aid system from working..

Odds are its a faulty sensor..

 

Well, being strictly logical, what are the chances that all 4 sensors have failed? My understanding is that if one goes you can still hear the others. All 4 are silent. Two I can see from underneath and they are connected (something I can't take for granted because a series of POs have really done some crazy stuff on this car.

As far as the *********** goes, I can get a replacement module for less than the cost of them telling me what's wrong. I agree it would be good to unplug/plug the connectors to make sure they are making decent contact and not corroded, but it seems such a remote possibility I'm not sure it's worth the effort to pull the bumper cover. Now if someone can tell me it's not rare for all 4 sensors to give out, then I would consider it.

 

You do realize that the reverse parking aid system is on the SERIAL DATA LINK network.
The Parking Aid Module has DTCs logged in the module that will help with diagnosing the fault.

You will need dealer level diagnostics but GUESSING can get expensive.

bob gauff

 

Hmmm. I was pulling on the connector tonight, and the park assist alert light on the switch was going off and on, and the speaker was squawking. Seems there's a bad connection there. The module pins look okay, no corrosion, so I'm wondering if I have wires broken inside the harness. Everything looks good on the outside of the wires, so when people talk about problems with the harness do they mean the harness gets rubbed through, or do the wires break inside the insulation where you can't see it? If so, where do they usually break? There are a lot of 90 degree curves in the harness which could possibly eventually lead to breakage?

 

Generally it's not been the harness. Yours may have been wet but you'll have to investigate to find what's wrong.