500E Car locks itself when engine is turned on

[janos_z]

Hey everyone,

My car has a new quirk: when I start the engine, the doors lock themselves. If I start driving with the doors locked, the alarm goes off as the car starts moving. I can unlock the car from the inside by pulling up on the door peg. The doors also unlock themselves if I shut the engine off.

A few other data points: the engine must be turned on for this to happen. Nothing happens if I simply turn on the ignition (position 2). Also, I can lock and unlock the doors as normal with the keys from the outside. Last, the ignition tumbler was recently changed because the original tumbler had locked up, though I don’t think this issue started immediately after it left the shop. The car also had an aftermarket alarm/remote lock installed by a prior owner many years ago.

It’s not clear to me how turning on the engine would have anything to do with the door locks but I’m sure there’s someone out the smarter than me... Thank you!!

 

[gerryvz]

I think it’s the curse of too many BaT comments on other 500Es....

 

[gerryvz]

I think your issue is a failure of the aftermarket alarm system. Likey an issue with the alarm’s brain box.

I was thinking that as I read through your post until I saw exactly that !! You need to REMOVE that system from the car. ALL of it. Try to preserve and improve the likely butcher job the alarm installer did.

 

[janos_z]

Haha yeah, I should have picked a different BaT alias for all my comments. I considered unhinged something or other, but someone else beat me to it...

Thanks for the suggestion about the aftermarket alarm; I’ve been thinking of having it removed anyway. AFAIK the actual alarm part had been disabled already; it’s just the lock/unlock feature the previous owner (and now, me) kept using. I don’t get why simply turning on the ignition (without starting the engine) doesn’t cause the fault. Either way, the electrical stuff should be on...

 

[gerryvz]

It's likely that something failed inside of the alarm's brain box and so it is sending a door lock signal when it gets energized when the key is turned and the engine goes on (evidently there is an immobilizer in the alarm circuit, as well).

If you trace the alarm and remove it, and patch up where the wiring was spliced into the system, hopefully that will solve the problem. Not unheard of as an issue, as these electronics get old and something fails and it doesn't work right.

 

[janos_z]

Thanks for the guidance, Gerry. That all makes sense. I'll get the aftermarket stuff removed and report back.

 

[sheward]

My first 036 had the aftermarket system installed under the wooden passenger side footboard. You might take a look under there to start as it's an area that provides access to the proper circuits.

drew

 

[gerryvz]

Typically I see the alarms installed under the driver's side on the dashboard (behind the steering wheel area) or in the center console under the radio. Most of the time in the driver's side under the dash.

 

[janos_z]

I had my car checked out, and Gerry called it! The good news is that the system isn't fried; it just needed to be re-programmed. When the car was in the shop, the battery was disconnected, and this caused the system to revert to some preset that included auto-locking the doors -- which then somehow triggered the factory alarm. Once the audio installer figured out what model my receiver was, he could reprogram it to not auto-lock the doors, and all is well.