Strange Driver's Door Locking Behavior - Mercedes-Benz Forum

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post #1 of 11 (permalink) Old 10-30-2010, 08:42 PM Thread Starter
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Strange Driver's Door Locking Behavior

We've got a 2006 R350 that has an intermittent problem that's driving us nuts.

Every once in a while the driver's door won't lock and the interior light will not shut off. Now you might be tempted to say "well the driver's door isn't shut bozo!", and of course that's exactly the behavior that is being exhibited...but hold on. Here all all the things that WON'T fix it:
  • Open and close the door repeatedly. No difference, still won't lock.
  • Turn the ignition on/off. Still won't lock.
  • Put the car in and out of gear (without moving). Still won't lock.
  • Swear, stand on my head, speak in German, still won't lock.

Now for the one and only thing that fixes it every single time:
  • Put the car in gear, drive a couple of inches backward or forward.

The dealer cant' figure it out. The car has been in many many times for this (like probably 10) and every time they say "we finally fixed it", and every time within a few days it happens again.

This sounds like a sensor problem of some sort to me, something to do with the drive train since it requires actual movement of the car to resolve it. However since I don't have access to the firmware or the schematics I'm pretty much out of luck.

Any kind and knowledgeable soles out there have a clue what might be happening here? Like I said, the dealer sure can't figure it out!
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post #2 of 11 (permalink) Old 10-31-2010, 07:35 AM
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well what has been done so far that the dealer says they fixed it??? i would say the door lock may be the cause but i assume the dealer has already tried that
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post #3 of 11 (permalink) Old 10-31-2010, 05:40 PM Thread Starter
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So far the dealer hasn't been ale to do much of anything. They've changed some module in the door but it hasn't helped. As I originally posted, opening and closing the door makes no difference, but moving the car a couple of inches fixes it every time.

Somewhere there's a firmware engineer who knows the conditions that will cause this behavior. That person could probably solve this in 30 seconds. Unfortunately nobody seems to know who that person is...
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post #4 of 11 (permalink) Old 10-31-2010, 07:13 PM
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well if it has been in 10 different times as you say and the dealer said they fixed it, what 10 different things were done to be exact???? you mentioned a door module, assuming it is the driver door control unit. still dont understand why a door lock wouldnt be tried, but.............
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post #5 of 11 (permalink) Old 11-30-2010, 11:31 AM Thread Starter
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Problem Located (I think)

So after literally months of trying to diagnose why the door won't lock, countless trips to the dealer, leaving the car at the dealership for them to drive for 3 weeks, replacing nearly everything in sight including the door locks, the ignition control module, the security system, you name it....I think I finally found the culprit here and it's unbelievable.

The parking brake (or something associated with it).

Last night the car was doing the strange door-won't-lock thing. I did nothing but release the parking brake...suddenly the door would lock properly. Put the brake back on. Still worked fine. Did some experimenting and discovered that if I veeery carefully depress the brake while counting "clicks" there is one and only one setting where the doors won't lock. Every time.

1-3 clicks: doors work fine.
4 clicks: driver's side door will not lock and interior lights remain on.
5+ clicks: doors work fine.

I can't count how many thousands of dollars have been spent on trying to diagnose/fix this problem, not to mention the months of frustration! Now to figure out what it is about the parking brake position that's causing this (probably something as simple as a limit switch).

How's that for obtuse???
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post #6 of 11 (permalink) Old 11-30-2010, 02:14 PM
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Just for clarification - when you say the door won't lock, you mean that it will 'latch' and stay closed, but you cannot lock it? That's with both the interior switch, and the remote on the key? How many doors affected?

The central locking system has no connection with either:

1. vehicle movement in gear, fore & aft (post #1)
2. parking brake operation (post # 5)

So their involvement with your fault can only be 'co-incidental'...

I can understand that you believe that they cause the problem to disappear, but there has to be a more logical reason for this fault. Possibly an intermittent connection on one of the several modules involved in the CL system.
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post #7 of 11 (permalink) Old 11-30-2010, 04:01 PM Thread Starter
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Quote:
Originally Posted by keyhole View Post
Just for clarification - when you say the door won't lock, you mean that it will 'latch' and stay closed, but you cannot lock it? That's with both the interior switch, and the remote on the key? How many doors affected?
The problem is that, under the described conditions (parking brake 4 clicks), the remote control will lock all three passenger doors but will NOT lock the driver's door. Additionally the interior light will remain illuminated. You can use the remote to try locking/unlocking all you want, the passenger doors will all work properly but the driver's door will not.

This is 100% repeatable. Depress the parking brake one more click and the problem goes away, all doors lock (with the remote) and the interior light goes off properly.

Quote:
The central locking system has no connection with either:

1. vehicle movement in gear, fore & aft (post #1)
2. parking brake operation (post # 5)

So their involvement with your fault can only be 'co-incidental'...
1. vehicle movement required me to release the parking brake. When I re-applied the brake I obviously depressed it either 3 clicks or >4 clicks. The movement was a red-herring.

2. Again, this symptom is 100% repeatable and depends solely on the position of the parking brake. Depress the brake 4 clicks...driver's door won't lock. Carefully depress it one more click...driver door locks.

Quote:
I can understand that you believe that they cause the problem to disappear, but there has to be a more logical reason for this fault. Possibly an intermittent connection on one of the several modules involved in the CL system.
Obviously there's some sort of connection between the parking brake and the central locking system. My guess is that there is some sort of sensor (perhaps as simple as a switch) that is not fully engaging or disengaging. Clearly something is sensing the parking brake position and that something is tied into the central locking system. I'll bet that armed with this info the dealer will find the problem immediately.

Last edited by gbaker; 11-30-2010 at 04:18 PM.
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post #8 of 11 (permalink) Old 12-01-2010, 05:28 AM
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Originally Posted by gbaker View Post
1. vehicle movement required me to release the parking brake. When I re-applied the brake I obviously depressed it either 3 clicks or >4 clicks. The movement was a red-herring.
OK

Quote:
2. Again, this symptom is 100% repeatable and depends solely on the position of the parking brake. Depress the brake 4 clicks...driver's door won't lock. Carefully depress it one more click...driver door locks.

Obviously there's some sort of connection between the parking brake and the central locking system. My guess is that there is some sort of sensor (perhaps as simple as a switch) that is not fully engaging or disengaging. Clearly something is sensing the parking brake position and that something is tied into the central locking system. I'll bet that armed with this info the dealer will find the problem immediately.
I do not have your model in my WIS. However, I expect that the only electrical item concerned with the parking brake is the S12 limit switch that is mounted on the pedal assembly. This is routed to the Front SAM module. An indication of it's operation is on A1e7 at the cluster.

Does this panel indicator light coincide with your 'click' experiment on the pedal? If so, try disconnecting the output. That will prove something.

The only possible 'connection' between the parking brake and the CL system is via the modules that take signals from both of them.

I am aware (on my CLK) that the parking brake signal is 'processed' by the modules, because if you move off with the parking brake still applied, an error message is displayed at the cluster. This must be recognition of the brake status, and wheel movement via sensors. But why this should affect door locking is a mystery to me.
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post #9 of 11 (permalink) Old 12-01-2010, 03:48 PM Thread Starter
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Right now I'm going to let the dealer handle it and see what happens (and I'll try to get a full report from him). The warranty expired yesterday but we've got an open repair order so that this will get handled at their expense. I don't want to go disconnecting anything until the dealer gets their shot at it!

No matter how it turns out I'm going to be surprised. I still can't figure out any reason to have the door locks and parking brake tied together. Somewhere at Mercedes there's a firmware engineer with a very strange sense of humor!
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post #10 of 11 (permalink) Old 12-01-2010, 06:35 PM
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My stab in the dark

Have you looked around (aka searched) on the R-Class forum yet? Your issue might have been encountered and/or solved previously. I'd at least look there and see. I guess you're lucky to still be under warranty status. Are there any other dealers within a reasonable distance? There's always a chance that your dealer is giving your car to a rookie tech who might be embarrassed (or too cocky) to ask for help.

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