Hazards and high beams flashing after locking, code 18 and 28 in LCM? 1997 740i

[THEhomelessONE]

A minute or so after locking the car, the hazards and high beams will flash, like the alarm is going off but no siren. I've read the LCM can be faulty or a hood switch can cause it. Finally got a new code that popped up.

Code 18 Connection to AHM, disturb. Quick search says it's some tow hitch module we don't have here in the States? The other code in the LCM is 28 Thermal oil level sensor, no idea how that has anything to do with the LCM but it's always there.

So what do you folks think? I'm out of ideas. The lights flash for a few minutes then stop. I think it does it at random hours but not sure. It does do it every time I lock it though. Battery is new and I can't leave it for more than a couple weeks without it getting pretty low or flat. Before it could sit for a month no problem.

[racer2086]

Few questions for you...

Does the siren work in general...like make noise? There are rechargeable batteries in it that go bad (especially in the pre-facelift cars with the wolf whistle siren). The wolf whistle has Ni-Cd and the newer sirens have Ni-MH batteries, which is why the new sirens tend to hang on way longer.

Also, the tilt sensors in the pre-facelift cars sometimes go bad and trigger false alarms. I asked about your siren, because it is possible the alarm is being tripped, but your siren is dead, so you don't hear anything only see the lights flash.

It does sound like you have a battery drain though, which can play all kinds of games with the electrical system and cause weird issues. May need to check/replace the battery and find the source of the drain.

[Mayorchuck]

Agreed. Sounds like a dying battery to me. I had one do the same thing years back.

[THEhomelessONE]

Weird thing is it only does it right after locking the car. I kept it inside the shop all day, never went off. The battery is a brand new Interstate 95r. Tested it after it sat around and it was about 1000cca. Interesting about the siren though, I'd rather not fix it in this case haha. But no I've never heard it go off. It would also do it with the last battery. Started happening after the rainy season, no water leaks inside the car, a bit near the battery though from a cracked tail light.

[racer2086]

Put the car in panic mode and see if the siren makes noise. The lights will flash and all just like if the alarm was set off. If the siren is dead, then the lights are flashing because the alarm is going off right after you arm it, which you want to fix. Since you have a pre-facelift, I would put a lot of money on the tilt sensor in the left trunk behind the radio amp. Replace it with a facelift tilt sensor (no liquid in the new sensors), and you will be good to go aside from the dead siren.

[THEhomelessONE]

Thanks racer, panic mode worked, light on fob was flashing rapidly, high beams and hazards came on but no siren. I'll try a new tilt sensor and report back. Most newer cars I mess with at work will keep a log of what set the alarm off, was hoping this generation had that feature.

[racer2086]

It does. You need DIS to look that up. INPA may do it too. Can't remember.

[THEhomelessONE]

Thanks, maybe I missed it I'll check again. Shop has a newer Autel Maxisys.

[racer2086]

It's kinda buried in the DIS menus. I'm pretty sure INPA will show it and be much easier to find.

[THEhomelessONE]

Hey was wondering if I could just unplug the tilt sensor? Thanks.

[racer2086]

Yes you should be able to. But you can grab a new version one out of the junkyard for cheap. The newer ones don't have issues like the old style with liquid.

[THEhomelessONE]

Thank you! So I unplugged the hood sensor, same issue after a few minutes. Fully charged the battery, unplugged the tilt sensor and it's still happening. Everything I've read says to check the hood and tilt sensors. My e38 doesn't have the motion sensor. I'm out of ideas Happens every time few minutes after locking the car.

[TheAngryBear]

Have you checked the siren?
The dying battery reference was to the battery in the siren not the vehicle battery.
Part of the system monitors voltage drop. A dead/dying battery in the siren will trigger this. Result being alarm going off.


2001 750iL DD74441
E65 fan & clutch, E65 headrests, Front First Aid Kit, Ultimate Cup holder

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[THEhomelessONE]

Ahh sorry I was thinking vehicle battery, but no the siren doesn't sound, so that was most likely the culprit. I ended up removing fuses 56 and 58 in the trunk by the battery and so far so good! Thanks for all the help everyone!