How ironic! Just as I put paid to the E39's rear parking-sensor issue, a front sensor goes on the E60... they do seem to be temperamental little things those same sensor-units used from the E38 up until 2008 - they can be working fine one moment and then just fail over night!
A few years ago one of my company directors had an E65 730Li, which started to spend a lot of time in our workshop under diagnostic. He blamed CANBUS issues and his symptoms were the car's electronics having a mind of their own, then as soon as one fault was rectified another would pop up straight away. I'm guessing the E60 uses the same technology as the E65, so can be forgiven for thinking mine might have the same issue seeing as the 'PDC' (parking-sensor) error came up the second I turned the key after fitting my new sidelight bulb...
Blown fuse?
The first thing to check, but mine wasn't blown and chances are yours won't be either, it's never the fuse with these BMW parking-sensors. The fuse is No. 21 in the glove-box, a green 30A.
Wet control-modules?
The sensors then fixed themselves for a day or two and then gave up completely, leading me to believe it was not just a failed bumper-unit. I hear on forums that intermittent PDC problems can be caused by a small amount of water being let in to the spare-wheel well while the boot is open and, without any drain holes, this can pool right where the PDC control-module is. Just a drop in the wrong place can cause erratic PDC behaviour and the module is fitted right at the bottom of here wheel-well, a bit of a design flaw, but it's only casually fixed in place on long wires so it's a good idea to move the module to a higher piece of ground somewhere else in the boot. I'll be putting up a guide for this as soon as I get round to it.
Broken sensor?
Yes. Those with vast experience tell me in 99.9% of these cases it's simply one of the bumper-sensors has thrown its hand in over night, which renders the entire system inoperable, as they work in a sort of daisy-chain. The only way to check which sensor is at fault is to kneel down at the front and rear of the car and put your ear to each sensor. As they work on a sonar principle the working sensors should emit a (pretty loud when your close) clicking sound. When you find the one that isn't clicking, that's your duff sensor - a lot easier than plugging the car into a diagnostic!
Sure enough, all my sensors were clicking away save for one - the front driver's-side centre one, ironically one that happens to be located under the headlight I removed to sort the parking-light issue, so I can perhaps see what happened there. It's too much of a coincidence for that sensor to fail right at that point in time, so it looks like I've disturbed something or allowed water into the back of the sensor somehow. I gave the wires to the sensor a good wiggle and traced them back to the loom, but still nothing, so got straight onto eBay and bought a replacement sensor. It's pre-painted in Titan-silver, having been pulled off an '04 E60 and was £33 delivered. This was a bit more than the E39 sensor, but I know it's the right part and it's still a lot cheaper than the £125 from BMW, plus the 2-3 week wait and fitting charge.
REPLACEMENT PROCESS:
For Front-Centre Sensors:
** This couldn't be easier. The official procedure and internet forums recommend removing the 'bumper-skin' to replace the middle-front sensors, which is basically the whole bumper. This is totally unnecessary! You can get to them through the lower grille and don't need to have tiny hands or be double-jointed. This is for non-M-sport bumpers, I assume the larger mesh-grille on M-sport models is attached from behind and would need the bumper to come off, but if it is detachable then this would be even easier. **
1. Remove the black plastic grille-bars from the lower grille by unclipping the horizontal bar from the lug at either side. This is done by lifting the bar and pulling it forward. The vertical bars simply pop off.
2. Reach into the grille aperture and up towards the corresponding sensor, you will feel the wires about 5-inches up.
3. Remove the wire-connector by pressing in the clip at either side and the plug should easily wiggle off.
4. Remove the parking-sensor from its mount by wiggling it from behind and slowly pulling it towards the rear of the car. At the same time, gently apply pressure to the exterior-face of the sensor with your thumb. Once it is about 2mm into the bumper it should slide out easily.
5. Push in the new sensor from behind, ensuring it is the right way up - that is with the single small lug and wire connector at the top (12 o'clock) - then plug the wiring connector back in and replace the grille-bars.
For Front-Corner Sensors:
1. Remove the headlight that is above the corresponding parking-sensor by referring to Steps 1-6 of THIS GUIDE.
2. The parking-sensor is located just beneath the outer corner of the headlight and is easily accessible from above. Refer to steps 3, 4 and 5 of the above guide to replace.
