TDI: Yellow Preheating Light Stays On?

Hello,

I hope I have fixed the error that was causing the yellow preheating light to stay on continuously.
For the umpteenth time, I described the problem to the ATU workshop.
(Trying to start the engine, but it won't start because the yellow glow plug light on the 1994 Passat TDI (260,000 km, top speed 200 km/h, range 1,900 km) is constantly illuminated, instead of turning off.)
Removed the 109 relay, short-circuited the socket with a cable provided by the ADAC. The engine started. After a few days, I reinstalled the 109 relay (one of the now three available) and the engine started normally. (And this somehow seems to be controlled by a random generator.) The mechanic specializing in electrical components for cars at ATU immediately suspected the electronic immobilizer. However, he doesn't have a wiring diagram for my TDI. I immediately searched for the control unit at home (it's located between the relay holder and the light switch) and disassembled it. Unfortunately, I couldn't see any obvious cold solder joints. Nevertheless, I resoldered all the relay solder joints.
And then, lo and behold, the engine now starts normally. The yellow preheating light only comes on briefly.
I will continue to monitor the starting behavior for a few more days, and then I will switch back to running in two-tank mode with 100% vegetable oil in the main tank.

Pöl_Passat

Ah, WFS.

It's stored in my engine control unit (ECU).

In addition, the indicator light doesn't flash when the "Wheel Function System" (WFS) is activated, such as when the small chip in the key is missing; instead, the engine simply turns off after a very short time.


Where do you get your information?
The university cafeteria often lets us down, so the T3 bus has had to run on diesel for quite some time now.

m;

'...the thing about the preheating lamp has nothing to do with the WFS (Warm Function System)... after the conversion to a 1Z engine, I didn't want to deal with all the hassle of learning the WFS, so I installed an engine control unit from an older 1Z model (without integrated WFS)... after the conversion, I also briefly had the problem of the glow plug staying on continuously without being able to start the engine... the diagnostic scan showed no errors... but after a few attempts, it went away, and now the car has been running perfectly for about 3/4 of a year.'

'Der frühe Vogel fängt den Wurm.'
1992 Volkswagen Golf III, fully equipped.
118,000 kilometers