I've ready every corner of the interwebz trying to find a solution for this problem and I've come up empty. I also have a Service Manual for this year and it's not been a lot of help.

Problem: Horn honking (pulse, not constant), Lights flashing and all doors locking will happen randomly when the car is off and unattended. This has been happening for more than two years. It is not temperature related. This happens when the Monty is outside and when it is in the garage. It happens in cold weather and hot. It happens in dry conditions and wet.

It is not the "Airbag contact short" problem. This is not a single long horn blast - it is beeping - and I can always stop it with a keyless remote button press. It has never happened when the engine is running.

The Monty will go months without this happening but when it starts it keeps doing it until I've either unhooked the battery or taken out the horn relays and let it sit for a few days (keeps happening but with horns deactivated I don't monitor it too closely). Eventually it will go back to the good.

This is what I know or at least think I know ...

1) I've eliminated remotes as possible source of garbage signals - remote batteries removed - still happens.

2) I thought that the doors locking themselves were part and parcel of the horn problem. They are unrelated. Today I verified that the doors lock themselves without the horns going off. Interesting data point - if I unlock the doors with the keyless remote they will relock themselves inside of 5 minutes. If I unlock the doors with the physical key (turn twice) the doors will not lock themselves. I've repeated the tests enough to verify this is true 100 percent of the time.

3) I haven't verified which horns are being activated when this happens but I believe it is all 3. It can happen with the Alarm/Theft Horn Relay removed, it can happen with the Horn Relay removed, but it can't happen with both relays removed (I'm only talking about the horns - the lights will still flash and doors will still lock). The circuit looks pretty simple - the high side wires go into the switch side of the horn relays and the ground side line goes through coil side of the relays and then to the ETACS. The ETACS switches on the horns by completing path to ground.

4) I've verified all door and the hood switch(es) work as they are supposed to although I guess an intermittent failure is still possible. I've stressed the wiring harnesses at all five doors with no observable problems.

5) Current battery was installed Sept 2014. Shows 12.4V no load and 14.4-14.7V with car running depending on load. Everything works on this rig - there are no other weird problems except one time when my wife said that the driver's side window did not go up after putting it down. I've not been able to verify that and it happened more than 2 years ago before we replaced the battery.

This is my current thinking:

Battery tests good but is starting to die creating uneven voltage conditions (I should reiterate this only happens when car is off). That's it, it's all I've come up with. Only because it seemed to be happening a lot right before we replaced the battery last time. 2 years isn't a long time on a battery but it's within the normal range and this car only gets driven about once every 1.5 weeks (only has 98k miles on it) so the battery goes a long time between charges.

Help? and Thanks in advance.

 

In case this can help someone else .... I had the Monty in for a transmission flush at the dealer because I was getting some torque converter slippage.

While working on my rig the tech got curious after listening to my description of this Alarm problem and at no charge spent some time trouble shooting. He claims that he found the problem was the hood switch and he was able to adjust it to eliminate this problem.

He didn't charge for the time he spent (so he's earned my business in perpetuity) and I'll be extra happy if I can go six months without the alarm going off.

On an unrelated note, it appears that TSB-03-23-2006 for torque converter shudder is spot on. I was experiencing that washboard rumble at 2k RPM in 5th gear when on flat or uphill and the transmission flush seems to have nearly eliminated it. Based on other posters it should disappear completely in another 50 miles or so.