florianjohnson17

Mercedes M Klasse alarm problem

My 2001 Mercedes M Klasse with a gasoline engine is acting up. The car alarm keeps thinking it's break-in night, but silently. I get an error in the memory, but the actual alarm never goes off. Doors, hood, trunk are all closed properly. Could this be a power failure issue, like a glitchy car alarm or even a battery issue triggering a false alarm? The whole alarm system is basically without function. Any ideas?

4 comment(s)

Sounds familiar. I had a similar gremlin in my M Klasse. Check if your alarm control module is coded to activate the optical locking confirmation, using the indicators to signal locking/unlocking. If it is, that could be your culprit. A voltage dip, maybe from a battery issue, can scramble the coding and cause the alarm to act wonky.

Optical locking confirmation? Hmm, that's a new one on me. How do I check that? Is it something I can do myself, or am I looking at a trip to someone with the right software?

You'll need some diagnostic kit to check that. SDS or similar. Honestly, unless you're familiar with coding stuff, best bet is to get it checked at a shop. It's usually a quick fix if that's the problem.

Turns out you were spot on. Took it to the shop, and they confirmed the optical locking was the issue. Recoded the alarm control module, and it's been behaving itself ever since. Bill came to 45€, which is a lot less than replacing the whole alarm system. Thanks again for your help!

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