AVF TDI im Passat 3BG: Kaltstartproblem | Posts 112+

The wiring harness hasn't been replaced yet because someone claims that if there's a contact problem, it will immediately trigger the EDC to store a fault code with the typical "PD-wiring harness error" message.
Should I not rely on it?

I've already tried the thing with the plug, but thanks anyway.

Greetings.

"Since I've already completed the troubleshooting, I can confidently say that the error isn't always stored. Two years ago, I dealt with a car that had a faulty wiring harness. Nothing helped by fiddling with it, and the error memory was also empty. It wasn't until I replaced it that things were quiet again, and you couldn't tell anything was wrong by looking at the old one!"

Okay, thanks. I guess I'll have to install the wiring harness too.

Best regards,

Hi.

Have you replaced the wiring harness yet?
I'm still having the same problem. I'm convinced it has something to do with the pressure elements and how the motor stops when turned off. I think one of the elements is leaking somewhere, and when it stops in a certain position, it leaks overnight. I've installed check valves in the supply and return lines, right before the tandem pump, but it's not working!
It's driving me crazy... and when it finally starts, which should take no more than 5 seconds, there's no smoke coming from the exhaust. There must be air getting in somewhere.

hmm

Hi!

"No, the wiring harness isn't installed yet. I've been using Ultimate and V-Power gasoline lately. Since then, the error hasn't reappeared. Maybe the fuel is "cleaning" the parts that are causing the problem. Perhaps the seals are behaving differently. I have no idea if it will help in the long run."

Greetings.

Hi.

I've only ever used "ultimate" fuel since I've owned the vehicle.
Often, it lasts for weeks, and often it malfunctions in the mornings and evenings.

Hi!

Yes, I experience the same thing.
I almost think it might be related to the tandem pump. It's just a guess. Maybe I'll have it replaced, along with the wiring harness for the PDs. Now that it's getting warmer again, the problem probably won't reappear for months.

Greetings.

Anyone experiencing starting problems with this A4 model should try something to rule out a possible cause.
Specifically, there's a problem with a diode in the light switch that burns out. This then confuses the car's onboard electronics when the ignition is turned on, which is why it takes 3-5 seconds for the car to start.
To rule out this error, the light switch should be turned on before starting.
Then it should start immediately, assuming that was the cause of the problem.
I tested this myself with a colleague, and it was 100% reproducible.
He had previously replaced everything that was suspected of being faulty, until he received this tip from a VW mechanic.
"New light switch for 90 euros, and the problem hasn't reappeared since."

Hi,

The Passat probably doesn't have the same type of headlight switch as the A4. Because, in my case, that method unfortunately didn't work. I was already familiar with this "insider trick."

Greetings.

Hmmm.

I've read about the light switch issue before, but someone needs to explain the whole thing to me.
I don't see any explanation for the starting problem... Also, it seems that the lighting on the switch is defective in every other A4, at least in the upper right area.

Regarding the tandem pump, I've already replaced the seal! By the way, there are two of them, and one of them had a continuous leak.

Best regards,

This is not an LED, but a semiconductor diode.
The error is not visible if any of the LEDs are defective.
As I mentioned, this condition confuses the ship's electronics, which is why the engine starts with a delay.
However, since the Passat uses the older light switch design from the A3 and similar models, it's probably not the cause of the problem in the Passat.

Hello,
That's quite a peculiar problem you're having. Question: What is the vehicle's mileage?
Could you please try starting the car in the morning like this? First, let it pre-glow, and then start it in second gear. I'd be interested to see how it behaves during startup. Best regards.

Have you already replaced the wiring harness? Mine is starting to do that again.

"Without a tachometer sensor (G28), it won't start... check the scan data above."

After more than 4 years, I doubt there will be anything more coming from this.