mkv golf tdi no glow plug light or power to ecu

[steveDay]

Hey Guys,
This is my OH car sorry for my first post being a problem thread!

Just recently when she has gone to start the car normally after the car has already started in the morning, she noticed the glow plug light didn't come on and the car would crank over but not start, she turned the ignition off and on again and then the glow plug light would come on and the car would start. Now I know the glow plugs aren't needed but my bit of research suggests when that happens there also isn't power getting to the ECU

I have a little OB2 reader and when I've got the same thing to happen ie no glow plug light, it can't communicate with the ECU. But when I turn the ignitions of and on until the glow plug light comes on it will then communicate with the ECU, but no fault codes.

Now I read on the Mk4 there was the infamous relay 109, I think the similar relay on the mk5 is 408 which sends power to the ECU, I've checked when I get the no glow plug light and it seems to be getting power and sending power to the ECU 12volts

I've also taken the battery out and the battery tray to check for bad earths and they seem all ok down there. I've also split the main fuse board in the engine compartment and the pins all seem fine.

one other thing I noticed when you get the fault is the fans will just kick in even when the temp gauge is showing cold, I don't know if that is related, it only does that when there isn't power to the ECU

any advice appreciated

cheers

 

[Henrick]

Check the 5 Amp fuses in the box under the hood.
Pull each one, check for clean and tight connection and re-seat it.

 

[steveDay]

I've taken apart the fuse box and split it and everything looks fine, I thought it might be fuse 458 which I think it's the main power supply for the ECU? but without a wiring diagram, it's hard to know!

 

[Henrick]

How frequently does this reoccur?

 

[steveDay]

It's actually been getting worse, I took it to a VAG specialist who has done some in-depth checks bypassing the ignition switch deleting the immobiliser. we are going to try a replacement ECU as everything else has been checked. ie fuses and relays

even the VAG expert is a bit stumped!

 

[firehawk618]

Too bad you're not in my area. My specialty is problems like you're having.

If the ECU doesn't show water damage then I really REALLY doubt it's bad but there's a slim chance.

Hopefully your specialist realizes that about all you can do with a used ECU is see if your CEL and glow plug light illuminate. The car won't stay running though with it due to the IMMO unless they know how to change the VIN and SKC in it.

 

[steveDay]

Yes I'm very much not local

He will programme the replacement ECU to the car if that's what you mean?

 

[Henrick]

O choose to vote for "the replacement ecu will not improve things" option.

 

[firehawk618]

Yes I'm very much not local
He will programme the replacement ECU to the car if that's what you mean?

Yes as long as you guys are aware a new / used one won't run without programming. But a new / used one should show the check engine light + glow plug light with key on so it could be useful to rule the computer out.

 

[steveDay]

All fixed guys, It was the ECU, replacement all programmed up to the car and working fine.

 

[Henrick]

Just wow...

 

[steveDay]

I have read up over the weeks on this fault, and a few times it has been the ECU. I was hoping it would be a relay or dodgy earth. Must be a circuit in the ECU that does the pre-checks before starting that fails, as the car never broke down, with the problem. just would never want to start up once it was warm, so a heat related fault in the ECU. A strange one for sure!

 

[Liammanu]

Please please help I think i have the same problem and I'm close to scrapping, mine is doing the same, very intimitent no glow plug light no engine management light but then sometimes they come back, how do i proceed in sorting it

I have read up over the weeks on this fault, and a few times it has been the ECU. I was hoping it would be a relay or dodgy earth. Must be a circuit in the ECU that does the pre-checks before starting that fails, as the car never broke down, with the problem. just would never want to start up once it was warm, so a heat related fault in the ECU. A strange one for sure!

Please please help I think i have the same problem and I'm close to scrapping, mine is doing the same, very intimitent no glow plug light no engine management light but then sometimes they come back, how do i proceed in sorting it