04 3 series BMW Rear Parking Sensors

kilclon

The rear parking sensors haven't been working for a while. Well they work the odd time but most of the time they just put out a continuous beep for a few secs when I go into reverse before going off. Is this something I can fix myself. Looking to sell the car now so is it even worth fixing? Its a 320cd m sport with 160000 miles

jayok

I had this problem on my 325Ci - it was the rear sensors over the exhaust system. To check, put the car in reverse with the ignition on but engine off. The closely put your ear to each of the sensors you should hear a "clicking" sound. If you don't then that sensor is gone. Get a replacement from flea-bay and you're off again.

Alanstrainor

jayok wrote: »

I had this problem on my 325Ci - it was the rear sensors over the exhaust system. To check, put the car in reverse with the ignition on but engine off. The closely put your ear to each of the sensors you should hear a "clicking" sound. If you don't then that sensor is gone. Get a replacement from flea-bay and you're off again.

Interesting! Must do that to mine when I get home.

jayok

Alanstrainor wrote: »

Interesting! Must do that to mine when I get home.

Yeah, the clicking you hear is the ultrasound being emitted from the sensors. Works with most. If you get clicking from all sensors but the unit still isn't working it's the control logic. Same strategy works with nearly all cars.

FWIW - BMW's sensors (Bosch) suffer in that the heat and muck above the exhaust seems to kills them. A common enough issue.

kilclon

jayok wrote: »

I had this problem on my 325Ci - it was the rear sensors over the exhaust system. To check, put the car in reverse with the ignition on but engine off. The closely put your ear to each of the sensors you should hear a "clicking" sound. If you don't then that sensor is gone. Get a replacement from flea-bay and you're off again.

Wow spot on. The drivers side one is gone. Are they difficult to replace?

jayok

kilclon wrote: »

Wow spot on. The drivers side one is gone. Are they difficult to replace?

Nope, there's a plug on the back of each sensor that you just plug out and then twist counter-clockwise (I think??) and out it pops.

You can do this if you're nimble enough without taking the bump off, but I couldn't For me, I just undone the left-side of the bumper and was able to reach in.

Took about 20 mins.

Alanstrainor

Legend! Mine have never worked, and I assumed it was a sensor but never knew how to troubleshoot it. Cheers!

kilclon

Just called BMW dealer for the giggle. Just under 200 notes for a new one. Ebay it is so.

unkel

kilclon wrote: »

Just called BMW dealer for the giggle. Just under 200 notes for a new one.

That's because they sell them in the original colours. And because they're the main $tealers, so yes they can!

On eBay for around half that if your colour is one of the more common ones. Or an unpainted one for about €25 shipped

jayok

kilclon wrote: »

Just called BMW dealer for the giggle. Just under 200 notes for a new one. Ebay it is so.

Reminds me of the conversation I had with the Dealer:

Me: "I'd like a rear sensor for my car"
Dealer: "What's the reg?"
Me: "03Dxxxx"
Dealer: "That's €200 incling VAT"
Me: "Oh I just need the one."
Dealer: "That's each"
Me: "What? €800 for rear sensors?!!
Dealer: "Yep, but they are genuine parts"
Me: "Er - no thanks"

Ebay genuine and my colour for circa €30.

kilclon

I haven't got the time or inclination to do this myself so how much should I be paying to get someone to fit the sensor. The whole rear bumper has to come off as I have the sport version. Just got a quote of €130 + vat and I thought it seemed ridiculous.

jayok

kilclon wrote: »

I haven't got the time or inclination to do this myself so how much should I be paying to get someone to fit the sensor. The whole rear bumper has to come off as I have the sport version. Just got a quote of €130 + vat and I thought it seemed ridiculous.

No it doesn't have to come off. Mine was an M-sport too. You need to unscrew the bumper from the n/s/r wheel arch and unclip the bumper upto roughly middle of the car. It will just hang off the back. The reach into where the sensor is, unplug the cable and twist out.

kilclon

Cheers. Would I have to jack the car up or can i do it on my back? Also, excuse my ignorance but what does n/s/r stand for?

jayok

kilclon wrote: »

Cheers. Would I have to jack the car up or can i do it on my back? Also, excuse my ignorance but what does n/s/r stand for?

Near Side Rear - that is the wheel at the back of the car nearest the pavement over the exhaust on the BMW you have.

Nope I didn't have to jack the car up or get on my back. Once the bumper was loose I was able to reach in from the top and get the old sensor out. That's why 130 + Vat is a bit too much for this! Honestly it was a 20 min job.

Bensmyth

Hi Guys.
My 320D E46 was the same, buzzer emitting continuously when in reverse for about 5sec.
I checked the sensors with my ear and diagnosed bot outside sensors were only barely clicking.
I bought two new ones from ebay (Aftermarket) and fitted them.

Now the buzzer does not go off when I put the car into reverse nor do the sensors work!
When I check them with my ear they are all clicking fine.

Is it because they are not genuine?
Anyone have similar issues?

jayok

Sensors need to be installed the correct way - i.e. you can actually put them in so the are not emitting the pulse with the correct shape. On the BMW ones I think there is a notch to ensure they are perfectly vertical, etc? Did you notice this?

BTW, when you say they are not genuine, all four sensors must be perfectly tuned for the modulator, are you sure they are correct?

Bensmyth

jayok wrote: »

Sensors need to be installed the correct way - i.e. you can actually put them in so the are not emitting the pulse with the correct shape. On the BMW ones I think there is a notch to ensure they are perfectly vertical, etc? Did you notice this?

BTW, when you say they are not genuine, all four sensors must be perfectly tuned for the modulator, are you sure they are correct?

They are fitted correctly as they would only fit the one way. I had the bumper off so I could see what I was doing.
I would say by listening that the two I fitted are not clicking as fast as the other two.
What do you mean by perfectly tuned or how do you do it?

Just to recap. All four sensors are clicking when I put my ear to them. But I'm no longer getting the warning beep inside the car to say there is a fault along with no beep when an item is placed near the rear.
The complete unit is OEM factory fitted and not an off the shelf unit.

delly

I have had the pain and suffering of a similar level with regards replacing sensors. I identified the one sensor over the exhaust that was causing the problem, so got an eBay replacement. Exact same symptoms as you, no fault beep, but nothing working at all. I then got other replacements from other sellers, thinking I may have the wrong type, yet it was the same result.

One thing to try is while the car is engaged in reverse, while ignition turned on, but obviously not engine, disconnect and reconnect each sensor one by one. Doing it this way, the sensors start to work after the reconnect, which is obviously useless but allowed me to see if any sensors worked ok. In the end I got it working by moving the two outer sensors and swapping with the inner sensors, resulting in three sensors working in total, but one inner one not, yet I get no error beep.

The long and short of it is that there is no exact science, but plenty of trial and error. One thing that other people online have said, who got sick to the teeth of eBay sensors, is that as soon as they went the main dealer route, no more errors. What one eBay sensor will work with another car, may not work with yours.

Bensmyth

Thanks Delly
I had noticed that too (When removing a wire from a sensor they would start to work) I'll try what you said and swap around the sensors to see if i can get them working.
I'll call the dealer today see what price new ones are. I'll post again when or if I get it sorted.

Bensmyth

Okay End of the road with this problem for me if anyone is Curious.
I eventually got back to looking into the sensor issue.

Putting an ear to the sensors (while car in reverse and key set to on) to listen for a sensor that is not clicking will not always work to diagnose a faulty sensor. Sometimes the faulty sensor will click too but will be slower or faint.
The next CRITICAL thing when ordering from ebay is to match OEM number's to your car. (There are websites that will do this for you)
I made this mistake thinking that all E46's had the same reverse sensor and discovered at my own expense that they don't.

After I actually bought and fitted the correct sensor that matched my car all is back working fine again.