Alarm going off on some mornings - already replaced hood sensor and IMS

[andrewwynn]

Sun is in a different position every day and takes months to move significantly. The symptoms would align with my suggestion that the seasonal change of sun position is why it came about.

Maybe you can set up a time lapse camera?

I'm thinking a stray beam of sun is hitting the car just right perhaps reflected off a house window or anything that can reflect IR light.

Uneven heating sets up some thermal stress and something binds until it "pops" making enough noise to set off sonic sensor.

Consider the concept of a door getting warmer than the body and eventually the door seal will move with a pop (similar to earthquake at fault lines). My tailgate seal was making a horrible squeak every time I hit a bump until I wiped a little bit of spray lubrication on it. It could be something in the car like a water bottle. Temperature and pressure changes can cause them to crinkle.

I've read the motion sensor can detect a bee or moth so they are very sensitive.

[andrewwynn]

Originally Posted by randywei

I tried to monitor the sun and how it hit roof area near where the IMS is, but it looks like the car is actually in the sun for a good amount of time before the alarm triggers (when it triggers, since it doesn't trigger every morning).

I'm wondering if maybe some connection to the IMS is loose and when it gets cold enough, metal contracts so the connection becomes an open. Then when the temperature warms up (i.e. via the sun), the metal will expand and make a connection again and that trips the IMS.

My impression is the sensor is sensing something not a connect/disconnect. I think you'd get a code for the device going offline.

I'm thinking something is heating unevenly and causing something to either bind and release like described above or dimple like an old timey oil can. (like a door panel etc).

[randywei]

Thanks for your suggestions and insight, @andrewwynn . Once I get the car back from the shop (assuming they're able to replace the recently swapped out IMS for a new one, under warranty) I did want to run an experiment of parking the car inside the garage to see if that makes a difference. Perhaps I can setup a time lapse camera as well.

At first I thought it may have been a bug inside the car, but then I would've expected the alarm to go off at random times, not just on random mornings around the same time.

Then the recent time when the alarm triggered right before noon after I flipped the car's orientation 180 degrees really threw me off as that was the first time the alarm went off so "late" compared to its normal ~8:20-8:30am triggering.

I know I can workaround this issue by double locking, but I really want to get this fixed if I can...

[andrewwynn]

Also you do want your alarm to be fully functional. It's tricky when things are intemittent.

You can put some cloth tape over the sensor to soften it's ability to hear and possibly help confirm the sensor is actually reading something.

Here's a thought; before I recently replaced most of my rear suspension I would get creaks and pops out of my suspension after I got out of my car. Lasted over a minute some times. There could be a similar situation where the suspension is binding and popping.

If you can figure out the alarm goes off when sun hits a particular corner of your car you can possibly park in the shade for a while then move into sun and sit inside and listen.

[randywei]

I came across this thread:

https://xoutpost.com/bmw-sav-forums/...off-alarm.html

I wonder if this is it...I do use the BMW sunshade and have been using it since we got the car. I've noticed that the wife sometimes doesn't secure the sunshade as well as I do...could it be that as the car warms up that if the sunshade isn't secured well it moves just ever so slightly to trip the IMS??

[crystalworks]

Originally Posted by randywei

I came across this thread:

https://xoutpost.com/bmw-sav-forums/...off-alarm.html

I wonder if this is it...I do use the BMW sunshade and have been using it since we got the car. I've noticed that the wife sometimes doesn't secure the sunshade as well as I do...could it be that as the car warms up that if the sunshade isn't secured well it moves just ever so slightly to trip the IMS??

I also habitually use the BMW sunshade. But I believe our alarms get set off regardless of whether it is in use or not, though have not tested it. Flipping the X5's around (both E70 and F15) so the front of the truck is not in direct sunlight most of the day has a 100% success rate on both vehicles.

[randywei]

Originally Posted by crystalworks

I also habitually use the BMW sunshade. But I believe our alarms get set off regardless of whether it is in use or not, though have not tested it. Flipping the X5's around (both E70 and F15) so the front of the truck is not in direct sunlight most of the day has a 100% success rate on both vehicles.

Interesting...sounds like it may be worth an experiment to try flipping the cars back to facing the sun and not using the sunshade?

[andrewwynn]

I would most certainly look into the possibility.