'96 E300D door lock snafu - PeachParts Mercedes-Benz Forum

landev · #1 08-21-2011, 01:02 PM

Well... I've hunted about in the threads, but haven't run across the exact situation I'm having.

It seems that I am unable to lock my car, either via the IR or key lock, but can lock/unlock via the switch on the dash. Using the IR remote, the lights on the mirror flash, but no locking occurs. Also, neither the fuel door nor the trunk are locking.

I initially thought I'd get around this by locking via the dash switch, then getting out and locking the driver door via the key. As I found out, opening the driver's door after locking via the dash switch unlocks all doors pneumatically.

Manually pushing down all the door locks, then locking the driver's door via the key seems to work, but unlocking via the driver's door then does not unlock the other doors. The key also fails to close the windows and sunroof as usual.

So, in a nutshell, it seems that the locking pneumatics only work when I'm in the car... not much use, that!

Any ideas would be appreciated.

Thanks in advance!

-l-

DAR2KMR2 · #2 08-21-2011, 07:22 PM

I had a locking problem problem with my '96 a couple years ago .... not sure if it had the same exact symptoms you described but if my memory serves me right the key in the door lock worked on that door only and the lock switch on the dash worked everything. I started with checking the fuses (always a wise thing to do) and I found that one of the fuses in the fuse box under the rear seat next to the battery was bad. I forgot exacty which one but it may have been the one that powers the security system. In any case I replaced it and all was back to normal. I haven't had a problem since so I suspect something weird must have happened when the car was off and locked that blew the fuse.

David Roseman
Long Beach, Ca

landev · #3 08-24-2011, 04:35 PM

Well, I'd have thought a fuse would be disabling the whole lock system, but it wouldn't be the first time I've been wrong! I'll take a look at the fuses this weekend and see if that might be the problem.

I'll let you know what I find out.

Thanks much for your input!

-l-

DAR2KMR2 · #4 08-26-2011, 03:54 AM

I believe Mercedes designed the system so that a single failure wouldn't completely disable the door lock and security systems and lock you out of or lock you in the car .... it's a German thing .... reduntant systems for safety. Since turning the key in the lock not only activates the electrical part of the door switch but the vacuum as well .... you get limited functionality when one or the other fails. I think the same system redunancy is built into the switch on the dash ... different electrical circuit than the security system. At least that is what I suspect. Good Luck!

landev · #5 08-27-2011, 06:21 PM

OK... I've had a chance to look at fuses. As you suspected, there's a blown fuse (#3 in the block under the back seat.) I replaced the fuse and the new fuse blew immediately... short circuit somewhere.

I'm poking about in the Star manual now, but am not having alot of luck in determining the faulty component.

I'll keep you posted and let you know if/when I figure out what the problem is.

Thanks again for your help on this.

-l-

DAR2KMR2 · #6 09-01-2011, 11:04 AM

If I were a betting man I'd put my money on one of the key locks (doors/trunk). I'd critically look at each of the door locks/receivers to see if one is cracked/damaged such that water could get in and short out the electric part of the switch. If they all look fine I'd suspect the culpret is most likely the one you use your key in most. At least that is my guess.

landev · #7 09-01-2011, 11:56 AM

Thanks for the pointer. I was also thinking that it must have something to do with the dirver's door. I replaced the door check on that door earlier this year... 'didn't notice any issues until recently. I was just unsure about how the electronics worked... I'm assuming that the mechanical opening of the door actuates a switch. I'll dig into it at first chance and let you know what I find.

I'm coming up on a fairly broad service session in a month or so, with new shocks, springs, brakes, tranny fluid/filter change, blah blah blah. I may put things off until then, but would like to attend to it sooner. Running the farm, working full time in town, and the
"honey-dos" make scheduling working on the cars a challange. As this is my daily driver, I'll get is squeezed in somehow.

Thanks again for your input. I'll let you know once I get this figured out.

-l-

landev · #8 11-27-2011, 01:10 PM

Well I've finally had a bit of "free" time to work on this door lock foolishness... still no resolution yet. I found by tearing the driver's side door apart that I would have to drill out some rivets to get to the locking mechanism and I didn't have the new rivets nor the time to deal with it as this is my daily driver.

I did, however discover that the pneumatic mechanism is hissing at the driver's door when I unlock the doors via the dash mounted switch. I'm guessing that the actuator needs to be replaced, though it still has enough "oomph" to unlock and lock the door.

I found a diagnostic in the Star manual that told to check the control module voltages for each door. Unfortunately I have no idea where these modules are located, so if any has a clue...

Thanks much!

-l-