TDI Relay 109 Failure: Passat Won't Start, Light On

Hello everyone,

After searching the forum for quite some time, I'm still experiencing an electrical problem, and unfortunately, I don't know the underlying cause yet. I hope you can help me with this...

It's a 1996 Passat 35i, engine code 1Z.

During a city drive, the preheating light came on and the engine stalled. The preheating light remains on continuously, even after waiting for extended periods and attempting to start the engine, and the engine will not start.


- After supplying power to the shut-off valve, the engine initially started again and the glow plug light went out, but this is no longer working at the moment.

- Relay 109 was hot (circuit board damaged) and caught fire after the repair was soldered.

- Current measurement at the working group for the re-soldered relay 109 showed that it was still shorting and releasing a current of nearly 2A.

- The glow plugs are glowing with approximately 30-35 amps (fuse in the engine compartment is okay).

- No tax voltage at the shut-off valve.

- Initially, the fault memory could likely not be read due to the defective relay 109; this will be checked again later.

- Replacing the electrical component connected to the Zünschloss did not yield any positive results.

- The wiring behind the fuse box is in good condition.




"Could the symptoms, as described here, be related to the immobilizer system, and where is the corresponding control unit located in the Passat?"

"Could someone perhaps provide wiring diagrams for the glow plug system or similar?"


I think I'll still try to get a new relay 109 today and test it, but I fear it won't help me.

Where should I continue my search, in your opinion? Unfortunately, I don't have any more ideas at the moment without having to obtain some potentially expensive spare parts, which I wouldn't be able to return after trying them out.


Thank you very much for your efforts!

Ralf.