Skoda won't start: Troubleshooting guide.

Hello everyone, I'm having problems with my Octavia Combi 1Z3 1.9 TDI, manufactured in 2006.
The car starts very well, then I drive it, park it, and want to start it again after some time, but the starter motor turns, the car tries to start, but doesn't actually start. I take the key out and put it back in, lock and unlock the car, and eventually it starts again. Then it runs normally again.
My friend had the immobilizer deactivated, which also disables everything related to it, such as the key, the reading coil, etc., because if the car starts, it would run for 1-2 seconds and then shut off again.
Mine doesn't start.
Speculations from the workshop suggest that some kind of relay might be triggering it, but that finding the fault would likely involve a lengthy search.
Has anyone else experienced the same problem, or can someone help me narrow down the cause?
The engine control unit (ECU) was indicated in the error memory.

A search for the famous "Relais 109" relay was unsuccessful. Can anyone tell me more about it, or if it has a different name when used in a Skoda vehicle?

Try keeping the organ running continuously for a longer period and see if the motor then starts.

No, it doesn't, and then it won't start.

I'm trying to find out which relay in my car is responsible for the engine control unit (ECU).

Was steht denn 1: 1 übernommen im Fehlerspeicher des MSG? Autoscan?

What is the engine's model code?

I didn't read the error codes myself; it was at the workshop.
It simply displayed an error message: "Engine control unit fault."

MKB is BKC.

"Try disconnecting the coolant sensor and then try starting the engine... just so you know, that will store an error code in the system's memory."

And please have the fault memory read out using VCDS.

Hello,

Please do an automatic scan like everyone else here and set it.

Until then, everything remains speculation, and based on the information provided, it's not possible to offer any meaningful assistance. Of course, you can unplug cables from all the sensors, but why would you? This is a diagnostic forum, not a guessing game.

The BKC engine is known for having cold start problems. If you disconnect the temperature sensor and the engine starts, you know that it's likely experiencing this issue.

matthiasTDI96 wrote:

Hello, Please, like everyone else here, do a car scan and set it up. Until then, everything remains speculation, and (based on the information provided), it is not yet possible to offer any meaningful assistance. Of course, you can unplug connectors from all the sensors. But why? This is a diagnostic forum, not a guessing game.

and we please adhere to that .
Herbert.

Hi everyone, it took a while, but here's the scan of the car.

Hello!

It's a shame that the engine control unit isn't providing any information. Now it's like searching in the dark.

Unfortunately, I can't tell you what might be causing that or what you can do about it.
Were any tuning modifications performed?

Basically:
There are two common problems with that.

"Immobilizer" has already been mentioned.
You can also tell by the flashing indicator light. At least, that's the case with my Golf; it also generates a typical error message.

The second thing is that warm engines sometimes need a certain starting speed before they are allowed to start.

This can happen when the battery is weak or the starter motor is sluggish. It's also possible that the engine starts immediately in winter temperatures of -10°C, but it still doesn't provide enough power for a warm start.
Once, my Golf had a similar problem. In that case, it was simply the battery.

Wenn ich mir aber die Spannungswerte ansehe, die das Protokoll an anderen Stellen mitliefert, sollte man mal die Elektrik prüfen, ob die Bordspannung tatsächlich so niedrig ist, und das dann in Ordnung bringen. VConceived in Lima!

Values below 12V are already concerning, and if that's actually the case, it could be the cause of various problems.