Audi A3 BKD 2007 non start, flashing brake warning and no ECU communication

[rocktheboat]

hi,

Looking for some pointers on this one please

Have a 2007 Audi A3 BKD engine. Has been fine until the other day - cranked, no start and the brake warning in instruments flashed up. After a bit of throttle it started and worked okay. Then the other day the fault re occurred but this time it was here to stay.

• Cant communicate with the ECU but can with other modules
• fans come on full speed almost straight away ( obviously engines cold )
• fuse check out okay
• swapped the relay "100" in engine compartment box for a known working unit - no change

I haven't got a wiring diagram but assume i either have a ECU power supply issue or the ECU is faulty

would appreciate some pointers please

[rocktheboat]

I would even appreciate if someone had a wiring diagram for this system and I could pin it out - thanks in advance

[Crasher]

The fans coming on show the fan controller (in the big fan) can see the what it thinks is a running engine but it cannot see a temperature signal so as a precaution it sticks the fans on at full blast. There is a command wire from the ECU to the relay which I have seen fail a number of times and the fault is buried in the harness so difficult to find, it is a stupidly thin (0.35mm CSA) and snaps. Message me your REG and email and I will send you the diagram.

[rocktheboat]

Ok I’ve done that thanks

what youve said makes sense but I’m always a advocate for a wiring diagram just so I can test it correctly

the relay in the middle of the engine fuse box has a “100” on it - I assume this is the ECU relay but I’m only guessing

I’ll wait for your email

[Crasher]

Bear with me, I just have to change a Corrado VR6 water pump first.

[Crasher]

Do you have the "low" as it is known engine bay electronics box with two relay positions, one with a metal bridge and one with a relay that has 100 on top and not four, is this correct?

[rocktheboat]

yes it looks as pictured

[rocktheboat]

ill await further instructions - ive had a read through the wiring diagram

[rocktheboat]

[rocktheboat]

So 12v at the red circles, then grounds at the top blue. The lower blue is the wire you said can break ( I know this will be 12v )