HELP! -- ML320 door locks and alarm gone crazy

Can anyone shed light on this problem with our 1999 ML320?
Normal operation of ML320 door locks: Door locks will self-lock when car speed reaches about 5 MPH, and stay locked until manually unlocked. Alarm
system is armed when car is locked via remote-control, and alarm will be activated if any door locked is unlocked from the inside (e.g., if someone is inside the car when it is locked).
Just-occurring, "crazy" operation of door locks: Door locks will self-lock as normal when speed reaches about 5 MPH, but soon thereafter, the driver door lock autonomously un-locks. If car comes to a stop, then resumes speed, all door locks will again self-lock (including the driver door lock), but very soon thereafter the driver door lock autonomously un-locks. This locking/unlocking repeats randomly as the car is being driven. When the car is parked and locked, soon thereafter the driver door lock autonomously un-locks, simultaneously triggering the alarm. If the car is left parked, the driver door lock appears to randomly cycle through periods of self-un-locking, then self-re-locking, each time setting off the alarm when it self-un-locks.
What's happening? There seems to be no fuse labeled as being specific for the locking system, which might be an easy way to at least solve the automatic alarm triggering problem. There seem to be at least two door-lock-related relays -- could one of these be defective?
Is this a common problem with a 1999 ML320? Anyone experienced this, and know the cause/fix?
Thanks!!
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This is a common problem. Look here for lots of details:
http://www.escribe.com/automotive/european/mbmc/search.html?query=door+locks
--

- RODNEY



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wrote:

Have the dealer change the lock setting so they don't lock automatically (supposed to be 9mph). I had the exact same problem and this fixed it. The dealer said that the 1999 model originally did not support that option but sometimes "accidentally" gets set on by a tech during other work on the alarm/locking system.
(My 1990 ML320 did not lock automatically until after the third time they tried to replace the locks and alarm. After picking it up from service I noticed the car locked at 9mph but it displayed the same things you describe. After three more days of poking around they told me the above and I did not have a problem since.)
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All models of the ML support automatically locking the doors at around 10mph. 1998 and 1999 models require a visit to the dealer to have the AAM programmed. On subsequent models (2000+), they added the ability for the owner to program the function through a certain series of steps involving the central lock button.

The problem is a defective door lock actuator sensor. What happens is that the door locks, but a sensor in the actuator doesn't recognize that the lock is engaged, so it release the lock. It is more likely to manifest itself when the automatic lock features is enabled because it will try to re-lock the door when the actuator sensor fails. This locking and unlocking can happen pretty rapidly, and is often called "machine gun door locks". Replacing the actuator is not an easy task. I believe that on the front doors, it requires some cutting and welding or riveting.
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- RODNEY



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