Anyone out there know what the cause would be for my rear door lock not "locking" (retracting) when I hit the "lock" button on my key? When I manually lock the door, and I hit my "unlock" button, the lock slides up. Another point: When I hit the lock buton, the motor runs for about 8 seconds or so (it is coming from the trunk - passenger side) - it seems excessively long to run.

I am guessing the actuator or something is broken. Are there any quck ways to determine what this would be? I

 

No there is a quick way, You will have to test the continunity of the acutuator. The window could also have a bad lifter or it needs to be greased. As far as the trunk, You didn't mention what model your car is, but on a C Class the lock pump, power lock distributor and actuator are located on the driver side of the trunk. My parts list doesn't show if the pump is electric or vacuum, so the problem could be back there, I do know the windows are both electric and vacumn operated. I would look there, as the panels are relatively easty to remove, Go to an auto parts store and get a panel puller, looks like a fork with two prongs, these are a great asset when remove panels and panel clips. There are quite a few parts,. typical Mercedes, that the power windows use, in each door, so it your not a DIY and familar with these systems I would go to a dealer or shop.

Another point my right rear window would not go up or down with the button on the console. I had to push let go, push let go to get it up or down., but it worked with the key. So I disconnected the negative battery terminal let the car sit for 1/2 hour reconnected the battery and went thru the sequence of resetting all the options in the owners manual, one of them are the electronic key and the power window one touch feature.
DO THIS FIRST AND SEE WHAT HAPPENS. While your waiting change the batteries in the key. I was interesting how this reset most systems. the instant start feature now actually works 100% of the time.

 

Allen: As usual, you're an excellent resource for us!

 

Thanks, I am fortunate to have a insurance company parts list, which has part numbers and locations of systems. Got it on Ebay for $5.00. Comes in very handy. Also, when I look at a problem like yours, I start with the easiest conponent to access first and work thru.