2003 1.6 BFQ Random Engine Shutdown - 17925 Main Relay Electrical Malfunction


Registered User
Driving steady at 70mph... suddenly dials drop to zero and engine shuts down. :flushed:

VCDS at roadside showed 17925 'Power Supply Relay for ECU (J271 or J363): Electrical Malfunction'

Car restarted and has driven normally for about 100 miles... (sigh, a serious intermittent fault :worried:)

Appears it relates to either a faulty relay, wiring, or an ECU problem...

I tested the ECU relay (429 in pic?) and it works perfectly.

I've cleaned the ECU earth point, which didn't seem corroded

I want to remove the ECU and check the connector for corrosion etc. However, the Haynes manual states:
'after reconnecting the wiring the basic settings must be reinstated by an Audi dealer using a special test instrument (!)'

Can I unplug my ECU to check the connector without harm? (obv. with battery out)

Have I tested the correct relay?

And has anyone else had a similar fault?

Thanks a lot



  • IMG_4008.JPG
    64.6 KB · Views: 1,198
  • IMG_4009.jpg
    81.4 KB · Views: 881


Registered User
Bump any takers?

Someone must have experience of removing and replacing their ECU. ..

A wiring diagram pointing to the relay in question would be great.



Registered User
I've had something similar, turned out to be a wiring issue. Some wires had their insulation cut years ago, and the "repair" wasn't waterproof. The symptoms slowly got worse as the last of the copper corroded away... Worth measuring resistance from battery to fuse, across fuse, and from fuse to ECU pin.
No idea about the specifics of the 1.6 engine though...


Registered User

Thanks a lot for the replies. Sorry for delayed response. Yes agree it should just be a TBA post ECU removal.

(Wow that linked thread is a monster)

I’ve managed to find a wiring diagram / schematic after a lot of searching.

Wiring tests ok... so I’ve sent the ECU off for testing.

Fingers crossed that will find a conclusive fault.

I’ve also ordered a new relay, just in case.

I did note my battery is maybe needing replacement (12.3V at rest). Possible this caused some error although I think I’m being hopeful here.

Will let you know how it goes.

Stuart B

Registered User
I have generally found when a battery is failing the first thing which stops working is the ability to start the car.


Registered User
Hello again,

So the ECU came back from the testing lab with no faults...

Good that I don't need a new ECU... bad that I haven't diagnosed the root cause.

I reinstalled the ECU and performed throttle body alignment and the car runs as normal.

However, I've recently had this DTC come up:

17700/P1292/004754 - Map Controlled Engine Cooling Thermostat (F265): Open Circuit

I've had this a few times over the last year and not worried about it.

Thermostat heating element resistance is fine (15.2 ohm).

So it could be the thermostat wiring...?

Interestingly, the wiring is (sort of) related to the problematic ECU power supply relay (J363).

Could these faults be connected?!

I've attached the circuit diagrams original and a simplified version.

Wiring checks out ok in terms of continuity.

I really need to locate the following connectors:

  • D52 "Positive (+)connection (15a), in engine compartment wiring"
  • G9 "Connection, in Simos wiring harness"
Does anyone know of a diagram showing these specific locations?

I don't want to have to unravel miles of cables.

Also I'm still uncertain how the J363 relay functions.... why does it need a relay anyway?



  • Simplified WD.JPG
    Simplified WD.JPG
    60 KB · Views: 1,097
  • WD.JPG
    121.4 KB · Views: 1,884


New Member
I have the same problem... When I drive my car(bfq engine) after 10min on driving, start the problem.when I push the clutch to stop the car engine shut down...