Door Lock Monitoring: How It Works

Hello,

My Passat 3B occasionally fails to accurately detect whether the rear left door has been opened.
The following has already been done:
* B-pillar connector -> Contacts cleaned and lightly treated with contact cleaner.
* A broken cable in the area of the B-pillar is unlikely, because the looseness wouldn't be resolved if the cable were broken.
* Türschloss zerlegt -> Leiterbahnen, Microschalter, Steckverbindung optisch u. elektrisch i. O.
* Comfort control unit -> Connectors visually in good condition (no corrosion, no moisture, everything looks new).

According to the wiring diagram, one of the microswitches is responsible for both monitoring the rotating latch (the "Schnappi" in the lock, which wraps around the locking bar on the body) and controlling the puddle light.
Now, the following effect occurs: The puddle light always turns on immediately when the door is opened. However, the bit for monitoring the door latch mechanism flips with a delay. If the door is closed for several hours, it takes longer than 30 seconds for the bit to flip (the vehicle relocks). If the door remains open for about a minute, it takes approximately 4-5 seconds for the bit to flip. If the door is opened and closed quickly in succession, there is no measurable delay.

How can I further narrow down the source of the error?

Bye.
peace

P.S.: I had just written a post very similar to this one, but then it disappeared. If it reappears from the digital void, please delete the thread.

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How can I further narrow down the error in a meaningful way?

What about the connectors on the door control unit?

If I'm not mistaken, the signals from there are sent to the comfort control unit via a bus connection. If the rest of the system is working, the problem might be in the connector, or between the door lock and the door control unit.

Hello,

vielen Dank für den Hinweis. Die Stecker am Türsteuergerät habe ich nicht erwähnt - allerdings hatte ich die auch in der Hand, als der Aggregatträger ausgebaut war. Da sEverything is fine.

It actually continues via the Comfort-CAN after the door control unit. This is also indicated in the wiring diagram.

Bye.
peace

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I didn't mention the connectors on the door control unit - however, I also had those in my hand

.

Too bad you didn't resolder the joints on the door lock.
Possibly, he's losing mass somewhere due to contact issues at low currents. This doesn't necessarily mean that the puddle light is completely broken. Perhaps you could check the resistance between the light's ground and the car body when opening the door, and/or directly apply ground to the corresponding contact on the door control unit to compare the reaction, in order to rule out the door lock as the cause.

Okay, I'll take the door apart again sometime. But I need to build up enough frustration about the error first. X

Bye.
peace


EDIT: I've temporarily moved the door control module from the left door to the right door. The error code is now appearing on the right door. This strongly suggests that the problem is located within the door control module itself.
Can anyone by chance obtain a circuit diagram for the circuit board in the TSG? The part number of the control unit is 3B9 839 751 CA.

EDIT 2: Yesterday, I tried a different used door control unit. The error didn't appear with that one. When I reconnected the original control unit afterwards, everything was working fine again. It seems we can only speculate about the cause.

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One can probably only speculate about the cause using this method.

Okay, I still suspect a cold solder joint or a loose connection. Let's see how long this issue lasts.

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cold solder joint, or loose connection

. However, this is likely only in the area of the door control unit. I opened it and had the circuit board in my hand - visually, no error could be detected. I also subjected the part to quite a bit of stress (mounted it on the other door, tapped it, shook it, repeatedly connected and disconnected it, etc.). The error was always reliably reproducible.

Perhaps it's possible that the comfort control unit had some kind of software issue. I briefly disconnected its connector, but maybe not for long enough to trigger a reset. It's possible that the other door control unit then activated a different sub-program or set a different loop condition, which resolved the "near-lockdown" issue. However, it's impossible to trace back now.

Perhaps you are right, and the error will reappear.

Bye.
peace

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I had opened it and was holding the circuit board inside - visually, no errors could be detected

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In such cases, I always try to find a solution if possible.

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I briefly unplugged it as well, but possibly not for long enough to trigger a reset.

Surely, it should also be possible to reset the device (in case the error occurs again) by disconnecting the battery.

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Reset... by disconnecting the battery

. I also think that, unfortunately, the idea only came to me now, after installing the other TSG and gaining insights from that. Until then, I assumed that the TSG was electrically defective.

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if the error occurs again

Now things have to be okay, I've been driving around with a disassembled door for weeks

Bye.
peace