Key opens doors but does not disable alarm

[mymymy]

Hi,

recently (about 10 days ago) I unlocked the car with the key fob (a C250 TD estate 1996 model) and when I opened the door the alarm went off. It kept going off whilst the doors were open. SHutting the doors and locking/unlocking would not turn the alarm off. I noticed that when I used the fob the doors unlocked but there was no beep to say that the alarm was enabled\disabled. Eventually I gave up trying to fix it, shut the doors and locked them. Next morning I tried again, and the beep was back, everything was fine. For a couple of days. Thenit happened again. Again after a while it worked ok and has been fine for about a week. This morning same thing.

Any ideas what the problem/solution could be? Otherwise I'm gonna get pretty good at getting both the kids and us in the car in under a minute so it only goes through one cycle of the alarm.

Thanks for any help.

Sam

 

[bigasotonuk]

Hi,
Have you replaced the fob batteries, the alarm and locking are two separate functions, the alarm side being more voltage sensitive, locking will continue to work while the alarm won,t disable.
Have you got red & green L.E.D.'s in the rear view mirror and in the drivers door, both the red & green L.E.D.'s need to work in both positons, as it can cause alarm malfunctions.
The red L.E.D. in my mirror was inoperative for 6 months, then alarm developed a fault MB replaced the L.E.D. perfect again. I doubted the diagnosis as it had been perfect even with the L.E.D. blown. But their diagnosis in this case was right.