Red LED on door lock always lit, VW Golf 3

Hello everyone in the forum!

"On my Golf 3 Variant (year 1995), I removed the alternator and disconnected the battery. After reconnecting the battery, the red LED on the door lock control has been constantly illuminated. This is still happening now, regardless of whether the car is running or turned off. The vehicle originally came with central locking, window lifters, and an alarm system. There are no error codes stored in the diagnostic memory."
Does anyone have a suggestion?

Best regards, Sascha.

A constantly lit red LED (at least in newer vehicles) indicates that there is an error stored in the alarm system. Can you access the alarm system using VCDS?

Is there really no error stored in the DWA control unit (and not in the engine control unit )? What happens during the actuator diagnosis of the DWA at the "LED" point?

If none of that works, I would simply disconnect the battery and reconnect it again. Perhaps the DWA control unit somehow got stuck (although I'm surprised you can start the car in that case).

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

Hello Guste,
I haven't found a separate alarm control unit (ACU). Just the immobilizer. And there's no mention of an LED anywhere. I've also wondered if the alarm system is specifically secured, although it would be strange that the LED always lights up. Disconnecting and reconnecting the battery didn't help.

Best regards, Sascha.

Zufällig im gleichen Zuge ein neues Radio eingebaut?
I'm aware of several cases where, after a change (e.g., system migration), certain IT infrastructure components like network services or data connections stopped working correctly.

Hello.
No, the Gamma radio remained untouched. I only removed the alternator because I needed to replace the water pump!
I can't find any diagnostic data related to LEDs or door contact switches in VCDS. There's nothing about it in WFS either; it doesn't have interior monitoring, and the central locking module isn't responding – could the problem be there? Because, theoretically, the Golf should have a central locking module, right? Everything else works perfectly fine, but this constantly illuminated LED is driving me crazy.
Has anyone ever encountered this error before?
I've seen before on a common Volkswagen Golf 4 model that the LED light stays on constantly, but unfortunately I don't know the cause.

I hope you can help me!

Best regards, Sascha.

It would be a coincidence, but...

- Possible cold solder joint in the vehicle's diagnostic control unit (if equipped - identifiable by the absence of a reading coil).
I would probably resolder those anyway, since they tend to fail quite often.
it could eventually lead to a failure of the DWA (Driver's Warning System) and prevent the vehicle from starting.

- Cable break in the wiring harness located behind the bellows between the door and the A-pillar?

Hey.
I'm familiar with the issue of a cold solder joint in the DWA module, as I experienced it with my old 35i. However, even then, it didn't allow the device to start up.
This particular Golf has a vehicle security system (VSS) and an alarm system (with a button located in the engine compartment).
"Does anyone know where I can find measurement data for the LED and alarm system in VCDS? Is it normal that the central locking control unit was not yet diagnostic-capable on the G3?"

Here's the error again:
The red LED next to the door pin is always lit continuously. It's on regardless of whether the door is open or closed, and whether the engine is running or not – it's always illuminated.

Has anyone else really encountered this error before?

Best regards, Sascha.

Quote:

Die rote Led neben dem Türpin leuchtet immer durchgängig. Egal ob auf/zugeschlossen Motor an/aus - sie leuchtet immer.

If connected correctly, the LED will receive a constant positive voltage (red/white) from the wiring harness in the door.

The other end connects via T32/9 (black/white) to T12/5 (red/gray) of the data cable.

Therefore, the assumption is that the black/white wire may be faulty due to a broken cable connection to ground or something similar.

Before checking that, I wouldn't proceed with further investigation.

"I find that interesting. I'll check for short circuits to ground and cold solder joints on the control unit tonight. What makes me suspicious is the fact that the error only appeared after disconnecting and reconnecting the battery. What do you think about the possibility that I damaged the control unit due to voltage spikes?"

Quote:

Was mich halt nur stutzig macht ist der Umstand das der Fehler erst nach ab und abklemmen der Batterie kam.

Me too . But you have to find something to do with your time somehow.

Short update.
"By the way, thanks for the pinout information!"
"When I unplug the connector from the control unit, the light goes out. All the solder joints look good. With the connector plugged in, there's a constant short circuit between red and gray wires when measuring continuity to ground. I'm going to leave the control unit disconnected for now and start searching for the faulty component."

Best regards, Sascha.

And here we go again!
Does anyone happen to know about the part numbers used for Roadside Diagnostics (RdD) control units?
The part number is 1HO 953 233D.
I could receive 1HO 953 233B.

Now the question is: Has the part number been replaced with a similar one, or can I not use this part at all?

Hello.
Here's some feedback regarding the solution to the problem!
I found a suitable part at a junkyard for 20 euros, installed it, and the alarm system is now functioning correctly again.
Make sure to pay attention to the correct part number, including any trailing letters.

Best regards,
Sascha

Hi TDI!

Vielen Dank für's Feedback zuerst einmal!

Have you opened the old standard grant application and taken a look to see if there's anything significant inside? If so, feel free to upload some pictures here.
The actual cause would interest me, because I still can't believe that something like that could happen when connecting or disconnecting a battery .

Best regards from Munich!

Hello.
Yes, I had the device open. I've seen some before with cold solder joints and other issues, but here everything looked perfectly fine.
For me, it was also the first time something like this happened. However, a friend who is an electrician said that this can sometimes occur, and that the risk of voltage spikes might be reduced by turning on the parking lights when disconnecting and reconnecting the battery.
"You never stop learning, and that's why I'm going to start doing things that way from now on."
Best regards, Sascha.