One of my parking sensor's packed up before christmas and i have only just got round to changing it,

This DIY is broken into 4 sections:
1 - Broken sensor identification
2 - Rear bumper removal
3 - Replacing with new sensor
4 - Fault finding

I only used a few tools:
  • 8mm
  • 9mm
  • 10mm
  • T50 torx socket
  • ratchet, extension bar and universal joint
  • selection of flat head screwdrivers
  • trim removal tool

1 - Broken sensor ID
This is the easiest part, turn your key two 2, so the engine is OFF but the lights and heater is on. Select reverse and go round the back, with your head at bumper height you can hear the sensors clicking, all four sensors should click, the one that dosent is the problem

2 - Rear bumper removal
This is quite simple and took around 30 - 45 mins
Firstly i ran my car up on to two scaffold boards just to lift it up slightly, you can do it from the floor but its a bit of a squeeze

there is an expanding rivit in each of the wheel arches that needs to be removed, the pin pulls out then the rivit, a trim removal tool will help but screw driver is fine:

Then above the rivit in the arch there is an 9mm bolt

Under the back of the bumper next to the exhaust pipe there is anouther expanding rivit that needs to come out:

There are two 8mm bolts and a 10mm nut under the back of the bumper near the exhaust pipe:

Then three 8mm bolts and a 10mm nut on the other side, the whole black plastic bit will now come off

The deffuser can now be removed, it is just cliped on, start at the exhaust pipe and pop the clips out from the back of the bumper one at a time, circled in red, there a few clips.

it just pulls off

There are two bolts with a star head that need to be removed. one each side

Once the bolts are out the whole bumper pulls towards you and off, watch out for the parking sensor wires, they are cliped up and can be uncliped so the bumper can be moved

To replace, reverse

3 - Replacing with new sensor
The wire can be removed easily from the sensor, there is a clip that needs squeezing on the bottom side,
With two flat head screwdrivers you need to pop the two clips either side of the sensor while pushing on the sensor from the bumper side, it will pop out

My new sensor was black,

So i sprayed it to match the others

Pop the new sensor in the same way as the old one came out, push the wire on the back

If you flip the bumper up right so that it istn facing the ground, switch the car to 2 again select reverse and you can check that your new sensor works

4 - Fault finding

So after installing my new sensor, it worked for a few days then packed up again :(

So the story/saga so far....

Original sensor broke a few months back, I ordered a new from ebay for 25. Which i painted and installed in the bumper and worked fine for about 2 days then the PDC stopped again.

I thought I cant be that unlucky to habe two sensor go so close together, can i?

Diagnosed as before listened for the sensor that wasnt clicking, it turned out to be the replacement sensor from ebay

So this made me think am I just unlucky to get a dodgy sensor from ebay? or is it something more, with the wireing? or even the PDC control unit?

So yesterday I had the bumper off again for a bit of fault finding

So firstly I removed the new (faulty) sensor and I removed a sensor that was next to it on the bumper, that i knew was working because it was clicking

I swapped both of the sensor arround to check that the problem was not with the wireing/PDC unit. Thankfully the new (faulty) sensor did not click in its new position, and the known working sensor worked in the position the faulty sensor came from.

So im going to be sending the fault sensor back for a refund.

While I was on ebay I found two sensor dor 25 very close to where I lived. So while the bumper was off I poped over in the van to collect them.

So in my haste to return home I didnt check the sensor properly and when i got in I relised that the sensors were ever so slightly diffrent:
Mine is the one on the left

Not a problem i thought, I had read on the internet that the tag on the plug can be filled off and the plug fits the sensor fine, and works as it should:

Plugged it in tested it, No luck :(

This time, I dont get the continuous bleep to indicate that a sensor has malfunctioned as before. But when i selcte reverse i get the normal beep beep beep to show its working, then it starts to beep as if something is behind me. But its not constant, with out moveing and nothing behind me it beeps then gets quciker as if im getting closer, then slows down again.

However if i reverse up to something on the side that the 'good' sensors are, and ignoring the beeps from the faulty sensor, it functions as it should until i get the continuous beep

So now my patentence is wearing thin and I really want this just to work

I tryed the seccond sensor that I got locally, still the same problem.

So far I have tryed three sensors:
Original from ebay - worked for a few days
2 sensors from ebay with wrong connectors - works but irratically

Now im thinking that its maybe the PDC unit or the wireing again,
After looking at the schematics for the PDC wireing here:
WDS BMW Wiring Diagram System - 3 E46
go to: complete vehicle>body>signel and warning functions>parking aid> selct your model

As you can see on the schematics, it reffers to a sensor as 'converter' it has three wires, which is the three pins i have on my connectors.
One is +ive (u), one is -ive (m) and the other goes back to the pdc unit for distance measurment (return) (d)

So in theory, assuming its 12v, you should get 12v between +ive (u) and -ive (m) pins in the connector and 12v between +ive (u) and return (d) but 0v between return(d) and -ive (m)

I unpluged all of the sensors and bodged up some test leads and cracked the multi-meter out:

I measured for DC volts between each of the pins on each of the plug for all of the sensors

I got around 12v as expected between each of the pins on all of the pins, this proves that its not the wireing or PDC unit at fault

So now my problem is do I buy anouther sensor from ebay? or do i just shell out the 75 - 90 and get a new one from BMW considering i have already spent 50 on sensors from ebay, although i do hope to return them

Yesterday i went to BMW and ordered a new sensor for 91!!!!!! painted

I collected it today and fitted it and it works fine