1Z Golf occasionally stalls (lack of control voltage at terminal 109)

Hello everyone,

A few weeks ago, I bought a Volkswagen Golf 3 TDI (1Z). I'm generally satisfied with the car, but it has a rather annoying problem with the electronics, which really takes away from the enjoyment of driving the TDI.

"During the ride, the engine occasionally shuts off intermittently, regardless of load, temperature, or other factors. Otherwise, it performs its function without any noticeable issues."
After approximately 90 seconds, it can be restarted again (whether the ignition is on or off), and it continues to run as if nothing happened – until the next malfunction.

Initial suspicion (after using the search function): Relay 109.
Okay, I tried the friendly approach, bought 109 [items/units/etc.] - no improvement.
Error codes checked: none found.

Next attempt, after a brief conversation with a master: Measure the voltage at the output terminal after it turns off. Multimeter in the car, and off we went...
Result: No voltage detected - after approximately 90 seconds, the expected 12V returned. (Ignition was on).

So, I temporarily bridged the cutoff device to the ignition circuit (terminal 15) for testing purposes.
Result: When the engine stalls, it continues to run (more or less *g*), but that's all, because the control unit is more or less switched off.

After some consideration, I finally installed my old 109 unit in the open position to see if it would close during the malfunction, and sure enough:
-> The tax voltage is missing (and returns to normal after the usual 90 seconds).

A look at the circuit diagram (at this point, thank you to my helpful colleague) shows that the 109 is controlled directly by the control unit itself. ZONK.
Since the control unit also receives a 5 signal from the ignition switch, I next had the ignition switch's wiring harness replaced -> no improvement.

I'm slowly reaching the limits of my knowledge now... Replacing the control unit and/or wiring harness is not an option due to cost (unless I find something cheap on eBay).

With the 109 bridged, the engine runs smoothly without any misfires, but I would like to fix the problem at its source.
I've also noticed that I've never seen the preheating indicator light up, not even for a second (the lamp itself is fine), even with the cruise control disconnected. Don't worry about it.

It all sounds a bit like there's a problem with the control unit, but maybe there's another explanation. What do you think?

Regards,
Bodo.

Hi.

If the motor runs when a 109 resistor is connected in parallel, it means that there is a constant voltage present at the relay input (terminal 30).

Therefore, the error can only be located on the "control side" = engine computer and the wiring up to that point .

There are definitely some potential weak points along the cable path: plugs, kinks, and even the central electrical unit itself...

You could, for example, try clamping a normal LED with a 1 kOhm resistor in place while driving with a bridged relay between ground and the connector contact G1/7, which is the switching line for pin 109.

When the engine is off, the LED should be lit; when the engine is running, it should turn off.

If the LED should ever light up or blink during operation, the interruption is located in the cable between connector G1 and the engine control unit (or in the engine control unit itself ).
If the LED remains off, there is possibly a break in the central electrical system between the relay socket and connector G1.

Furthermore, the wiring harness for the engine control unit (ECU) is also a possibility, as it's through this harness that the command "turn on power for the EDC" is received.
It runs from terminal 15, via connector G1/4, to pin 38 of the engine control unit.

If there's a misfire, the engine computer interprets it as a "misfire" and shuts off the engine.
It's logical that there's nothing in the error memory, because the engine computer thinks "everything is normal" .

"The usual 90 seconds" after which the engine can be restarted suggest a problem with the thermostat, and the relay itself gets quite warm when the engine is running. Therefore, a loose connection directly in the relay socket would be a strong contender.

Unfortunately, the initial warm-up stage of the engine control unit for the 109 will likely also be affected... however, one should then be able to vary the waiting time, for example, by adjusting the engine control unit .

Good luck .

Good idea, thank you.

I'll look into that right away. What I find interesting is that it always takes roughly the same amount of time before it can be restarted. If I disconnect the 15 (e.g., with the ignition key), it can be restarted immediately. That already points to the 109.
I'm also going to temporarily disconnect the sensor labeled "109" while the engine is running to see if that results in a 90-second delay.

Is it possible that the anti-theft system is involved here? He doesn't have an immobilizer yet.

Strange wrote:

If I disconnect the power supply (e.g., using the ignition key) from the control unit, it can be restarted immediately. That already points to the 109.

Hi.

This virtually eliminates thermal fluctuations.

Quote:

Could it be that the anti-theft system is involved here? He doesn't have a

immobilizer yet.

If the DWA electronically blocks the engine in an emergency situation instead of just making noise, of course.

However, that applies to the ignition switch (number 15), but not when the engine stalls. I can do whatever I want with the ignition, but the waiting time remains.
(Did I phrase that unclearly?)
The intention was that if the signal "15" is missing from the control unit, for example, due to a loose connection in the wiring harness, the waiting time would not occur.
Because if I normally turn off the ignition using the key, I can immediately restart the engine.

The LED part is mostly finished; I just need to reinstall the old relay to bridge the connection.
When not bridged, the LED only indicates whether 30 volts is present, and it seems stable and secure at times.

Strange wrote:

However, the thing about the 15 (ignition switch) does not apply in the case of a misfire. I can do whatever I want with the ignition, but the waiting time remains. (Did I phrase that unclearly?)

Hi.

Then, the suspicion remains that there was a problem with the temperature reading.

Keep us updated. Your case is something of an "exotic" here...

Hi,

I've now manually detached the 109. Result: sometimes it could be restarted shortly after, while other times it would restart immediately afterwards .
Perhaps I should do this more often and statistically record it...
But what about the thermal aspect?

I also installed the device with the LED. If I haven't misunderstood something, the LED is only showing a current of 30, which is flowing through the relay coil and the LED to ground.
So, it's always on when the ignition is on.

Okay, I also couldn't find anything similar in the search results.

Regards,
Bodo.

Strange wrote:

I also installed the device with the LED. If I haven't misunderstood something, the LED is only showing a current of 30, which is flowing through the relay coil and the LED to ground. So, it's always on when the ignition is on.

Hi Bodo,

No:
a) 30 is the constant-on setting, so the LED will initially stay lit continuously (therefore, it's better to only connect it while driving, but a car battery can usually handle a discharge current of around 10 mA for a few days ).

b) However, if the engine control unit activates the relay, it pulls the other side of the coil on the 109 to ground, causing the LED to turn off due to a "parallel short circuit" (when the ignition is on).
Specifically, this continues until a potential fluctuation occurs between the LED connection point and the motor controller, at which point the current flows again as in scenario (a).

Okay?

Hi,

*click* Yes, you are right. The whole thing works as expected. No signal from the control unit -> LED on, otherwise LED off.
But as is often the case with these things, when you're waiting for the error to appear, you don't see anything.
So far, the LED remains stubbornly off, while the motor continues to run.
I will let you know as soon as anything changes.

Regards,
Bodo.

So, I also had that problem before, on a Golf 3 with a 1Z engine, manufactured in 1994.
The engine simply stopped working and then started again sometime later.
I fixed the problem by resoldering all the contacts in the immobilizer control unit.
The immobilizer module is located somewhere between the steering column and the light switch.

They always told that story about the relay at the friendly place.

Good luck.

cs wrote:

I fixed the problem by resoldering all the contacts in the immobilizer control unit.

Hi.

. . . but the vehicle being discussed here does not yet have a WFS .

Hello,

It doesn't have WFS (Window Film System), but it does have an anti-theft alarm system. I've worked on it before, and I only found one solder joint that looked loose, which I resoldered. It didn't really help, though.
If I manage to get it out again with the built-in dashboard, I'll definitely overhaul them all.
So far, I haven't experienced any further issues. Maybe it's because of the pulling at the back of the ZE (Zündspule/Ignition Coil) or because I disconnected the connector from the control unit a few times (but it didn't look corroded).... I don't know.
However, I'm already wondering myself, because normally, since I've had the car, I've experienced an average of 1-2 instances of this problem per day.
However, the preheating indicator still isn't working. This is probably due to the control unit or the wiring (unfortunately, I don't have a wiring diagram for that). Relay 103 is also not switching.

Regards,
Bodo.

Strange wrote:

So far, I haven't experienced any further issues. Maybe it's because of the pulling at the back of the ZE (Zündspule/Ignition Coil) or because I disconnected the connector from the control unit a few times (but it didn't look corroded).... I don't know.

Hi Bodo,

It can be either.

Quote:

However, the preheating indicator still shows nothing. This is probably also due to the control unit or the wiring? (Unfortunately, I don't have a wiring diagram for that)

It's located between pin 15 and a pin on the engine control unit, so it doesn't actually share any connections with pin 109. It seems there's another issue here (blown bulb when it's not even an LED, broken wire, loose connector, etc.).

Quote:

. Relay 103 is also not switching.

When should it switch?

Hi,

I think it should glow, or rather, it should be glowing.
Unfortunately, I don't have a schematic diagram for that.
Hopefully, I'm not completely talking nonsense here .

Regards,
Bodo.

...no interruptions

Strange wrote:

I think that if it's glowing, or rather, should be glowing. Unfortunately, I don't have a schematic diagram for that. Hopefully, I'm not saying complete nonsense here

.
Hi Bodo,

I'm too lazy to walk to the car right now, but if the glow plug relay (number 103, position 2) has two really thick pins, then that's the relay.

The indicator light usually turns on for about 1 second each time the ignition is switched on.

HELLO

"I ALSO HAD A SIMILAR PROBLEM. A customer's Golf 4, model year 1998, with engine code AHF, suddenly stopped working. I replaced the relay (number 109), but it didn't fix the issue. Every time the preheating light didn't illuminate during starting, the car wouldn't start, and it wasn't possible to diagnose the problem. The error code 1552 didn't respond. Then, after an hour, it started working again. Finding this fault was very stressful. I checked all the power supplies, and they were all okay. The only thing missing was the voltage from the control unit (SG) to activate the relay 109. I then installed a used control unit, and the car has been running perfectly ever since."

GOOD LUCK WITH TROUBLESHOOTING.
MARCELLO