False alarms

Tony Francis

Tony Francis

Zorg Addict
British Zeds
Joined
Jul 22, 2023
Points
56
Location
South Somerset
Model of Z
Z3 1.8 M43TU
Still trying to hunt down the cause of random false alarm triggering on my Zed. I have changed the bonnet switch and repaired all the wires in the boot loom. The car managed 2 days of silence this week then the alarm went off again this morning for no reason - it’s parked on my driveway and I can see it from the front window so I know there were no scallywags about!
So a question for the collective wisdom - does the car store any codes that would tell me which sensor is triggering the alarm, and if so can I access that information through the OBD or any other way?
 
I had this problem, it was as Ant says the tilt sensor. It was completely under water. It was the aerial grommet letting in water. If you lift the boot carpet up behind the passenger side rear light you you find a well. If it has water in that is probably the problem
 
Thanks for the advice gents. I did look in the well where the tilt sensor is fitted when I was doing the boot loom, it was dry in there but I must admit I didn’t remove the sensor to check for corrosion. I’ll get in there again for a more detailed look!
 
Had a few minutes before work this morning so have been back in the boot to examine the tilt sensor. No wet in there, took it out & disconnected, no signs of corrosion, pins & plug are clean. If I tilt the sensor I can hear a rattle from it but I guess that is just the mechanism operating. so I have refitted it but left it unplugged, locked the car again and we will see what happens!
 
Well disconnecting the tilt sensor has not fixed the problem, silent for about 3 hours then went off again. I will plug it back in.
So back to my original question does anyone know if the car stores any codes relating to alarm triggers that can be read through the OBD that would help to identify which sensor is causing this?
 
Tony hi ..what about if you lock it with the key? Is there anything in the stack of service history related to the alarms or locks ? I am still perplexed that I never had this issue in 2 years of ownership.
 
Hi Ant, no nothing in the comprehensive maintenance records that seems to relate to any previous alarm problems . I have tried locking with the key and the remote, tried the two presses on the remote or two turns of the key to isolate the interior sensor, everything works perfectly, alarm indicator light flashes correctly. In fact everything on the car is working perfectly - apart from these random alarm activations. I am now wondering if it might be one of the door lock switches - i guess they can wear over the years.
 
Have you looked at the condition of your battery? My understanding is if the standing voltage drops below a certain threshold, the alarm can trigger because it thinks it's being tampered with. I've had false alarms when the car's been off the road a while getting work done. They stopped after the car was run a few times (i.e. battery charged back up).
 
Thanks for the suggestion, I did wonder about the battery voltage but Ant fitted a new Bosch battery a couple of years ago, the car isn’t used everyday but a couple of times a week at least, not short journeys, so it should be getting enough charge. I haven’t had any problems with starting or any indication that the battery might not be holding charge.
 
I would think.the problem is the drivers door catch switch. Simply down to the fact it will have much more wear than the passenger's side. You can try wrapping a few turns of insulation tape round the pin the catch locks on as a temporary measure.

Tony.
 
Even though you have changed the bonnet switch, try disconnecting it for a week and see what happens.
 
Do Z3’s have motion sensors? I’ve had a few false alarms with no apparent cause, but I did notice once that my suction phone mount had fallen off the windscreen into the footwell, which might have triggered an alarm if there was a motion sensor.
 
Thanks for the further suggestions gents. Obviously best to try one thing at a time so I will start with drivers door catch/switch as suggested by Tony. Appreciate all your help.
 
I don't think mine even has an alarm.... :(
 
Tempting fate here but the false alarm activations have stopped for 2 weeks now. Trouble is I don’t know why as I haven’t done anything else to investigate the problem. Not complaining though …….
 
Mine does that every now and then. Stops for months then does it again for a bit then stops
 
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