[whitenblue]

Two months ago I installed an aftermarket hitch from etrailer.com with an aftermarket wiring harness that splices into the rear tail lights. When I tested my trailer everything seemed fine.

Fast forward to this past weekend when I tried to put my bike rack on. The rear bumper proximity sensors went crazy and emitted a constant tone as they sensed the rack. Clearly there must be a work around or some option to disable the sensors when the rack or a trailer is mounted.

That brought me to the following question. How does the factory BMW hitch and wiring harness work??? Wow. I just found the F25 hitch installation instructions online and I can tell you the factory hitch wiring harness and system is VERY integrated into the existing car.

So now I'm wondering about a few things.
1. By using an aftermarket hitch wiring harness and control module, will I lose functionality and/or destroy anything?
2. How do I get around the bumper sensor problem?

I'm second guessing my approach going aftermarket, but the price difference was remarkable. BMW quoted me $2000 installed. I paid $220 for the aftermarket hitch and wiring harness and did it myself in a few hours.

Thank you.

[najnad]

I have an aftermarket hitch on my X3 as well, I have the OEM hitch wiring harness, havent installed it yet. But from what I have read, even with OEM wiring the parking sensors will go off if you have a bike rack on the hitch.

The OEM wiring, once a trailer is plugged into it, will disable the rear parking sensors. Not sure there is a way to do that with the aftermarket wiring.

[dtox9]

Im new to the bimmer world... so I'm guessing that maybe your 35i doesn't have the same button by the gearshift to turn off the parking buzzers that my 28i has...

It's super convenient when the drive-thru is lined with bushes and when i get close enough to the window to get my food, the stupid sensors are screaming... LOL...

Is there something in bimmercode perhaps?
(yes - a pita to code your car every time you haul your bike... but....)

[najnad]

Why would the parking sensors go off in the drive thru? Mine only come on when in reverse or manually turning on the cameras. You could turn off the cameras with the button you mention, but then kind of defeats the purpose of having the cameras (surround view, not just rear view).

[HPR]

Originally Posted by najnad

Why would the parking sensors go off in the drive thru? Mine only come on when in reverse or manually turning on the cameras. You could turn off the cameras with the button you mention, but then kind of defeats the purpose of having the cameras (surround view, not just rear view).

The parking sensors are a bumper mounted ranging system and sound off because of some perceived obstacle being within a certain distance...18"-24" I believe. Cameras allow you to see the perceived threat but do not activate the alarm.

In bumper-to-bumper traffic mine sound off occasionally when someone behind me gets too close. Here in Colorado in the winter they'll also sound off during a heavy snow storm when snow and ice build up on the bumper(s).

[najnad]

Originally Posted by HPR

The parking sensors are a bumper mounted ranging system and sound off because of some perceived obstacle being within a certain distance...18"-24" I believe. Cameras allow you to see the perceived threat but do not activate the alarm.

In bumper-to-bumper traffic mine sound off occasionally when someone behind me gets too close. Here in Colorado in the winter they'll also sound off during a heavy snow storm when snow and ice build up on the bumper(s).

Must be an LCI thing...the sensors on pre-LCI only are active when the cameras are on.

Perhaps you have the driver's assist and its blind spot warning that is sounding the alarm?

[HPR]

Originally Posted by najnad

Perhaps you have the driver's assist and its blind spot warning that is sounding the alarm?

No blind spot warning system on the car. As I indicated, it's a radar based proximity sensor that will alert you when you're too close to something.

[FranzX3M]

The sensors should only go crazy when trans is in reverse and maybe park. Once you start driving it should stop. Its annoying but you have to live with it or get the BMW OEM trailer install kit and I think some programming may be required but I'm not sure. I think the module detects when a trailer is hooked up to the harness and suppresses the back up sensor. I never tried a bike rack, only a trailer. If the peeping continues when you are driving then have your tried to push the camera/park assist button on the center console by the gear selector and see if that stops it?

[Giznaz]

Plugging in a trailer light system is what turns off the alert from the PDC's.

No trailer lights, alarm sounds.

You could make a dummy plug with resisters to simulate a trailer, that will defeat the alarm. I purchased the resisters to make one, but haven't gotten around to making it yet.

I found the info online, don't recall resister value or where I found it, but it's out there somewhere on the interweb

Some of the newer cars alert when in drive if something gets too close. My wife has an I3 that goes crazy parking in the garage

[bpwj76]

I have a Curt hitch mounted on my X3 and when I have my hitch-mounted cargo carrier on there the PDC goes crazy, but only in reverse. It stops beeping once I reach approx 5mph or so. I wonder if deactivating the Auto PDC option in iDrive would stop it from doing that.

[whitenblue]

Guys,
First off let me thank you all for replying. Participation is what makes this work, and crowd sourced information is a very powerful tool.

Example - I didn't even know about the PDC button next to the gear shift! I'll have to try that out. I probably don't know 80% of what my X3 can do. It's hard to dedicate time toward being a BMW IT professional just to learn your car. Haha.

I have the higher capacity Draw Tite hitch from etrailer.com. And this wiring harness:
https://www.etrailer.com/Wiring/BMW/...leID=201738108

I didn't like cutting and splicing into the left and right turn signal wires, but I didn't realize there was another option. I actually called my dealer to inquire about OEM hitch and harness options and specifically asked the parts guy, "does the factory harness require splicing into existing wires?" He returned and said yes. After reading the factory harness installation procedure he wasn't lying; but it's just one splice into the right turn signal wire, the rest of the factory harness seamlessly plugs into existing connectors and modules ready and waiting in the car. Damn. That, and the BMW hitch module, is what gives the functionality to sense when trailer lights are plugged in. My harness just siphons off signals from the car's rear turn signal lights and relays them to the connected trailer. I should add my hitch harness is powered directly from the battery so it doesn't draw down the car's rear turn signals.

I guess I have two options at this point:
1. Buy the factory harness and redo it. Which is a lot of work, probably a few hours.
2. See if the PDC button gets me by.

Although those two solutions only apply to when I have trailer connected. If I just have my bike rack mounted I'm going to need the PDC button or a simulated trailer anyway.

[whitenblue]

One more thing. I just read the manual. in iDrive there is a way to turn off automatic PDC activation:

Cut and pasted from the manual
--------------------------------------------------
You may switch on and off automatic activation when obstacles are detected via iDrive:
1. "My vehicle"
2. "Vehicle settings"
3. "Parking"
4. "Automatic PDC activation": only with respective equipment.
5. "Automatic PDC activation"

The setting is stored for the driver profile currently used.

If necessary, switch off automatic PDC activation on obstacle detection, e.g. in vehicle washes, reduce false alarms.
--------------------------------------------------


So maybe that's another option for us.