Non Starter, 17925 - Power Supply Relay for ECU

So today i tried starting the 24V lump, And it wouldnt start

I have the following VAG-COM VCDS Code:
1 Fault Found:

17925 - Power Supply Relay for ECU (J271 or J363): Electrical Malfunction
P1517 - 004 - No Signal/Communication

Now i have removed the 2 relays in the engine bay and using a 32 relay in the ECU socket as per rubjonny. I dont think this is the issue though as i am getting 12V on ECU pin 3 which i think is the main feed for the ECU? This comes from G1/10.

Im not sure this is the issue as the ECU seems to be powering up.

I have also checked 12V on the coils through the single plug (Black/Purple cable) and thats fine.

Not sure on the injectors though. They are going to G2/08 and are only reading 2-3v at the T14a plug (Red/Purple wire)
On turning the engine over this seems to go negative , Pretty sure thats not right?

What can you suggest for me to try or test please.

Im pretty happy with the 1 code so far though, There was a couple of others but i think that was due to a dead battery. 100 later the engine turns over very well!

Thanks
Mat

 

I can't remember the actual diagram, but the ECU switches on the relay to suppy a larger current back to the ECU - likley it can't see it switching, the ECU switcheds it by earth

do you have a live on pin 85, or 86?? the other one should be the ECU switch

 

Wow, Thats complicated!
Does anyone have a pin-out for the ECU plug?

 

that should read Din 85 or 86 of the relay of the ECU power supply , fed from 30amp fuse 37 of the std fuse box - same relay that feeds the coilpack in OEM install

 

I will check that tomorrow

One thing i have in my mind so far is the ECU power.
Looking at the diagrams and posts tonight there should be 2 connections for power for the ECU, A constant and a Switched.

I know i have a constant on T121/3 but cant remember what feeds that, But im pretty sure i have a single black wire tucked away in the loom. One of them should feed T121/62.

 

Do you have a link to this diagram?

I have long de-installed my copy of etos as it took up too much space.

J393 is the central convenience unit relay so is not applicable.
"J271" relay suggests the PCM has not sent the ground signal to the relay control circuit via KL85 to switch on the output stage to coils, lambda heaters and so on.
The relay control circuit should also have a live on KL86, which should feed back on the ECU. ( I am talking this off the top of my head based on standard VW format and a diagram for your 24v motor would help confirm)

That ECU is not seeing a return resistance on the appropriate pin T121/?? and is reporting that diagnostic.

 

Thanks toyo, I have e-mailed you the diagram.
Remember I have removed both relays from the bay and wired it back to the CE2 fusebox using a 32 relay.
I think what I'm looking for is switched live on T121/62

 

good to see your at the start her up time,shame it didnt start.

 

From your diagram, this is how the PCM is powered by relay J271

KL30 -> T121/62 and J271 pin 1. Permanent live ( for keep alive memory. Stores aircharge, ignition and fuel adaptives, allows current flow through T121/23 during 'key on')
J271 Pin 2 KL 87 -> T121/3. Switched live to ECU as well as Coils and VVT solenoids ( dependant on KL85 going low).
J271 Pin 5 KL 85 -> T121/23. ECU earth to relay control ( the fault is suggesting up this is not working)
J271 Pin 4 -> Switched live to fuel injectors ( dependant on KL85 going low).

 

so it looks like its just an earth problem on ecu?

 

I doubt there is a disconnection at T121/2 and 1 (PCM earth). If that was the case diagnostics would not function.

 

KL30 -> T121/62 and J271 pin 1. Permanent live ( for keep alive memory. Stores aircharge, ignition and fuel adaptives, allows current flow through T121/23 during 'key on')
That one i have to check. Diagnostics only work with the key but does the ECU allow diag with the key off from standard?

The ECU is earthed by T121/2 & T121/3, I have checked all them. One thing i picked up somewhere else is that the chassis of the ECU should be earthed, Does this sound right? Might is just chucked on the ECU plate so i doubt it is earthed itself.

 

I cannot see how T121/3 is an earth. Switched supply +12v KL87 from J271 to PCM, coil packs and vvt solenoids via "f" track.

I have combined the pages to make it easier.

 

I agree with Toyotec here, pin 23 is switching on the relay to feed battery voltage to pin 3 & the coil packs
if your getting a earth on that wire looks like the relay isn't switched on, and showning a earth from the other consumers ( trust the force on that one!)

Edit : explains orignal fault code relay not right?

 

Ok so i have checked the 2 connections on the ECU.
I have:
T212/3 - G1/4 & T121-62 - G2/9
Both these connections are fine so i guess like RJ says, Its just a code because that relay has now gone.

My problem is with the T14a and the injector connection i think.
My current setup is this:

Engine loom: Car loom:
T14a/5, None T14a/5, Red/Purple - G1/10
T14a/8, Red/Purple T14a/8, Black/Purple - G2/4

I dont have a connection engine side for T14a/5 which is listed as "switched live to injectors" so it must be using pin 8.
Should i be using G1/10 for T14a/8 really?
Obviously im using G1/10 for T14a/5 which i dont need now as my engine does not use that connection.

 

Oh, and yes the fuel pump primes and I'm sure it's running when cranking as I had a leak on the fuel rail and it ****ed out when cranking. I can't hear it but im sure it is.

 

I am getting quite confused about what is going on having read both the 24v diagram and the fact that you are integrating this powertrain in a MK2 Golf with a late central electric fuse box.

The ECU always has a live feed, as in a MK4 it is woken up via CAN i.e. when you open the door to prime the pump. The logic in the ECU disconnects the internal connections to Power and earth after a time out.
The warning with the J271 relay, or lack of, can be made to shut up if you like with an alternative circuit to power the ECU.

To/From BDE J220	Golf CE2	Description
T121/62	Pin 4 from Digi relay (Pos 3) or H1/1	Permanent +12v with 20A fuse
T121/3	G1/10 (need Digifant relay fitted)	Switched +12v
T121/23	*With alternative PCM power up relay	ECU earth signal to J271 control
T14a/8	Z1	Injector supply +12v
T2/1	G1/4 (KL15)	Coil pack/VVT/intake tuning flap
T121/58	N/A	CAN H (Pin 6 on a J1962 CDC)
T121/60	N/A	CAN L (Pin 14 on a J1962 CDC)
T121/65 -> T6/2	G1/3 (Assumes F/P realy in Pos 12)	F/P relay ECU earth signal to J17
T121/54	N/A	VSS from cluster that daisy chains with ABS/ESP module or gearbox sensor (02J)
T121/43	??	W Warning to cluster module MIL 1J K83?

*Alternative PCM power up for T121/3 to clear fault.
Obtain a 4 pin automotive relay and connect:
KL30 -> Permanent Live
KL87 -> T121/3 only not T2/1
KL86 -> G1/14
KL85 -> Triggered by T121/23


Originally T14a/8 is powered by J271 via pin 4. If this relay is missing or is substituted for another that is not activating or has no link to this connection your injectors will be closed.
However the suggestions given above should get the engine started

 

Wow, great post! Thanks!

So the simple solution is to swap my T14a/8 to Z1 to power the injectors.
I can live with the code, it is a track car after all and it won't throw up an MIL I dont think.
I have not wired in an MIL light yet but will do it now I know which pin it is.

 

come on dose it start then.