Random starting fault, not cranking, no codes, relay 645 trick

[Baltazar]

Hi there,
2-3 times a week my 2016 T6 (150cv) simply won't start in the morning (regardless of temperature, humidity level). Upon turning the key, the dashboard lits up normally but the engine doesn't try to crank. back in July and again last week, the official dealer could not find any codes and only suggested to replace the ECU. Since I wasn't ready to pay 2000€ yet I found a workshop that could clone a second hand ECU but unfortunarely this did not fix the issue. Interestingly while I was checking the fuse box I found out that removing and repositioning the 645 relay in its spot (terminal 15) fixes the issue most of the time! When it doesn't, then I have to wait until the next day when it usually starts...
I'm at a loss because the official dealer has no diagnotic, cloning the ECU did not change anything and the relay trick is not a sustainable solution.
I need my vehicle everyday and I've spent too much on rentals, any help would be appreciated!
Cheers,
Balta.

 

[oldiebut goodie]

Haven't you tried replacing the relay - appears to be quite vital:

Switching and auxiliary relay, identification number: 645, used as a relay for low/high heating power, fog lamps, fuel pump, heated rear window, start-stop ...
€6.45 · ‎In stock

 

[Baltazar]

I thought the 2 workshops that looked at the issue 3 times would have ruled this out as the cause of the problem especially since they told me to replace the ECU... anyway I have ordered a replacement to make the swap myself. that would be both hilarious and outrageous if the solution was that simple. thanks for the tip! I'll keep you posted.

 

[Dellmassive]

try swapping out the relay, - as above

and check the socket terminals for water ingress and corrosion.

and possibly spread terminals, causing poor connection.

 

[vdiksas]

Hello guys,

I have a simillar issue. Have you succesufully resolved it?

Thanks

 

[Baltazar]

Hi, not yet, swapping out the relay did nothing. Van was at the workshop (not dealership, expert in car electric, electronics) for 2 weeks for a diagnostic but it started flawlessly every single day so theycouldn'tsee anything. I took it back and of course the next day it didn't start... after ruling out all external factors (humidity, temperature...) it seems that the fault will more likely happen the next morning after a long journey. Do you notice the same?

 

[vdiksas]

Hi, not yet, swapping out the relay did nothing. Van was at the workshop (not dealership, expert in car electric, electronics) for 2 weeks for a diagnostic but it started flawlessly every single day so theycouldn'tsee anything. I took it back and of course the next day it didn't start... after ruling out all external factors (humidity, temperature...) it seems that the fault will more likely happen the next morning after a long journey. Do you notice the same?

I have a weird situation regarding this problem. I had both EGR and DPF deleted on my T6 2017 150hp (285k kilometers) and after that sometimes it would not start. No crank. If I would hold the key turned, it would crank but with (what I assume) little resistance. Like low compression.

The funny thing is that when the van does not want to start (I tried multiple times) - I plug my OBD device - go into Engine LiveData and then - 100% of the time I get the car running. That have happened +10 times already. No error codes.

I imagine that would have something to do with cam or crankshaft sensors. I have the car returned to the shop where they have done the EGR and DPF work. They cleaned some kind of valve which they assumed could be the problem because it closes when the engine is shut down. Sorry I could not recall what kind of valve exactly that is.

I am wondering what could be the reason for that and if someone have experienced something like this.

Thank you for your thoughts and ideas.