W202 Alarm - very odd issue

grahamcol

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I've had my 1996 W202 C200 (pre facelift) for 7 years now and it has been a great car. Just lately, however, the alarm (actually the 2 main keys, I think) has started doing something odd. Long story short, if I alarm and disarm using the flat "emergency" fob all is well. However, if I use either of the main keys, I very often get a situation where the alarm will not arm (if disarmed) or will not disarm (if alarmed). Whenever this happens the red led's in the mirror flash for about 40 seconds - together, if I remember correctly. The c/locking works every time though. I've put new batteries in and done a re-sync etc, all to no avail. As I said, if I use the flat emergency key it all works fine 100% of the time. Could it be the two main keys are both in need of replacement ?
 

television

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Not a key issue at all, if the car unlocks then the keys are fine, more like a mirror or alarm fault
 
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grahamcol

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Not a key issue at all, if the car unlocks then the keys are fine, more like a mirror or alarm fault

Thanks as always Malcolm. However, I simply don't understand how it can be 100% perfect using the flat emergency key which I've used for 2 weeks now, yet it failed this morning using one of the "proper" keys. As soon as I used the flat key again it was fine.
 

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If locking with the remote key fob, then this arms the alarm / immobilizer .

If you unlock with the metal key in the door lock the alarm should still be set

I am not sure what this emergency thing is that you have
 


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