OBD accessories trigger the car alarm?

[esskay]

Wondering if others have noticed this phenomenon of OBD accessories triggering the OEM car alarm?

I have a 2017 FL S3. I recently installed a P3 gauge, which connects via OBD to read data from the vehicle. The car began to occasionally sound the OEM alarm when I locked/armed the car, for no apparent reason.

After much confusion and trial/error, I finally figured out what is causing it. If I have an OBD accessory plugged into the car’s OBD port (I tested this with the P3 gauge and a BlueDriver bluetooth OBD scanner), and I lock/arm the car twice in a row in reasonably quick succession, the car’s OEM alarm will go off. It didn’t matter whether I use the key fob or the smartkey door button, and it also doesn’t matter whether the car could sense the smartkey was in proximity (i.e. whether I’m standing right there or farther away).

The alarm doesn’t go off if I just lock/arm once, or with enough time in between locking. I only discovered this issue because of a strange confluence of factors — after an unpleasant experience many many moons ago with forgetting to lock my car at the time, I became paranoid about forgetting to lock my car. So I always double check that my cars are locked after parking. In the case of my S3, when you hit lock on the key fob when the car’s already been locked for a little while, it only flashes the blinkers (no confirmation beep). When you hit lock again, it’ll beep. So sometimes when walking away from the car, I hit lock on the key fob twice in a row in order to hear the beep. I don’t normally double-tap to lock, it’s just because my S3 won’t beep without it.

All good, car always behaved fine... until I installed the P3 gauge and the alarm started going off occasionally. I finally realized that when the P3 was plugged in, if I lock/arm the car twice in a row, quickly, it would trigger the OEM alarm. I plugged in a BlueDriver OBD scanner instead, and the same thing happens.

My theory is that Audi has some sort of OBD security sensor in the OEM alarm, and perhaps when arming the alarm twice in a row, it gets triggered by the OBD accessory the second time. For example, perhaps the first arming causes the OBD accessory to briefly emit a signal or read data or draw power or something, which the second arming detects thus triggering the alarm?

I didn’t uncover much on this topic by googling, though I found several discussions about BMW alarms being triggered by some OBD accessories (e.g. Valentine 1).

Anybody have any thoughts on this? Any suggestions besides unplugging the OBD port or avoiding double-tapping the key fob or door handle? TIA!

[esskay]

Hows the P3 wired? Where does it get its 12v from?

As I have it configured right now, the P3 is just plugged into the OBD port. I don’t have any other external sensors or leads on it right now, it just picks up data (and power) from the OBD port.

Similarly, the BlueDriver is a bluetooth dongle that just plugs into the OBD port, then you use a smartphone app to check codes, etc.

[aaronc7]

17 S3 here. I've used OBDLink, OBD11, Ecutek and now Cobb AP constantly plugged into it. Never had alarm go off once or any other weird issues.

[MikTip]

https://www.advanced-incar.co.uk/201...theft-protect/

[esskay]

Since P3 offers the OBD plug...I would ask them.

Or did you configure the OBD connections?

Wire it to different 12v /ground source.

The P3 gauge is connected via the OBD cable that comes with it. The car alarm also triggers when my BlueDriver bluetooth OBD scan tool is plugged in instead of the P3 gauge, so it’s not just the P3 gauge that this happens with.

[esskay]

17 S3 here. I've used OBDLink, OBD11, Ecutek and now Cobb AP constantly plugged into it. Never had alarm go off once or any other weird issues.

If you have a chance, while you have something like your Cobb plugged into the OBD port, could you try locking the car twice in reasonably quick succession to see if anything happens? Please try it when the car is already locked.

Everything is normal on my car except for when I double-tap the key fob or door button.

Thanks!

[aaronc7]

Sure, I'll give it a go tomorrow

[MikTip]

I'm guessing its a security measure VW/Audi has developed to counter thefts by using OBD devices...

Audi is very secretive about this stuff...

Perhaps contact P3...ask if they know any solution or reasoning for...

Contact your local Audi dealership...ask them if they can switch it off?

I've found info relating to...but no solutions...

[aaronc7]

I tried multiple OBD devices plugged in, was not able to get the alarm to sound or any other sort of abnormal behavior.

My car does a confirmation chirp every time I lock it though... I don't have to do it twice to hear it. Maybe this is a setting in the MMI but I don't recall seeing it.

That's the only thing else that stuck out to me vs what you said in your post.

[esskay]

I'm guessing its a security measure VW/Audi has developed to counter thefts by using OBD devices...

Audi is very secretive about this stuff...

Perhaps contact P3...ask if they know any solution or reasoning for...

Contact your local Audi dealership...ask them if they can switch it off?

I've found info relating to...but no solutions...

Yeah, the simplest explanation would seem to be that somehow it’s triggering an OBD alarm sensor. My solution thus far has been to try to avoid double-tapping the alarm. I just did it again last week at Walmart as I was walking away from my car and set off my alarm. Of course, I had parked way in the back the of the lot, so no one noticed. LOL

[esskay]

I tried multiple OBD devices plugged in, was not able to get the alarm to sound or any other sort of abnormal behavior.

My car does a confirmation chirp every time I lock it though... I don't have to do it twice to hear it. Maybe this is a setting in the MMI but I don't recall seeing it.

That's the only thing else that stuck out to me vs what you said in your post.

Thanks for testing your car so thoroughly! That’s very kind of you, much appreciated!

It’s interesting that your car behaves differently when locking. To put a finer point on it, if I lock from the door handles, I believe mine will always emit a confirmation chirp. But if I lock from the key fob, if the car has been sitting undisturbed for a little while, it’ll just flash the parking lights without a chirp. If I’ve recently locked the car and hit the key fob, it’ll chirp right away.

Yeah, I don’t remember seeing anything in the MMI settings relating to this, besides whether to chirp at all IIRC. My 2017 was manufactured early in the model year if that makes a difference.

[jnhalstead]

have you done any custom coding via obd11 or VCDS? if you have an open current do to coding it will set the alarm off. When I was doing my DRL as blinker on my 17A3, I had the coding wrong on the driver headlight and it would set the alarm off if I tried to lock it after the alarm was fully set.