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?


(https://flic.kr/p/2gqantC)https://live.staticflickr.com/1833/43190298644_900ece6b91_o.jpg (https://flic.kr/p/28Nzz4s)

[rocktheboat]

yes it looks as pictured

[rocktheboat]

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

[rocktheboat]

http://i22.photobucket.com/albums/b338/G340UTT/4F8F6788-5805-43CA-8E34-A873E493842B.jpeg (http://s22.photobucket.com/user/G340UTT/media/4F8F6788-5805-43CA-8E34-A873E493842B.jpeg.html)

[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 )

[Crasher]

Remind me tomorrow, I did write a long reply to this but it looks like I did not send it, probable got dragged off to do some real work.

[rocktheboat]

will do - I appreciate your help with this.

[Crasher]

If you have no power from the relay, jump pins 1/30-2/87 so as to directly power the ECU. If this makes it start then change the relay.

[rocktheboat]

I must have power going between 1 and 2 as the fan works until I take the relay out. I did jump 1 and 2 to test and now change.

However I have 12v @ pin 5,4 and 2. Don’t seem to have anything at 1 ( although the fan starts running straight away until the relay is pulled )

[Crasher]

We need to step back a circuit

[rocktheboat]

Ok -where now

[Crasher]

Tomorrow

[rocktheboat]

Ok

[Crasher]

You are going to have to take off the ECU chastity bracket and unplug it so you can test the feed to the ECU plugs pins.

[rocktheboat]

Okay, and what pins please mate. I’ll take off tomorrow night

[Crasher]

You need to check for ignition live (line 15) at pin 18 of the 94 socket plug (the large one) which ultimately leads back to fuse 2 in the dash side fuse board, I have seen these blow due to faulty brake light switches. You should check for ignition on (line 30a) power to positions 3, 5 and 6 (the larger pins to one side grouped and 1, 2 and 4 are the earths)of the 94 socket plug and if nothing, continuity back to fuse 13 in the engine bay fuse board which comes from the relay terminal 87 on the socket marked 2 on the board.

[rocktheboat]

Hi, I’ve finally got around to having another go on this -

Needed to remove the anti tamper screws on the ECU holder

Can you / have you got any more detail regarding the pins of the ECU plugs ? I know you’ve said the numbers but have you a picture or are there numbers cast into the housing ?

Really want to get the the bottom of this and really appreciate your help

[Crasher]

There are tiny numbers moulded into the receiving case of the ECU which you have to reverse in your head and look back at the plug to use, or on the reverse of the plug, when stripped down, the numbers are also moulded in but to view any of these I have to use two pairs of glasses and a watch makers magnifying glass, a consequence of getting old. This is why VAG insist on using plug in break out boxes which plug into the cars harness and then into the ECU, giving easy measuring access but these are rare, expensive and difficult to find so we all have the struggle so BEWARE, it is VERY easy to strain and damage the plug pins and they are awful to replace.

[KK26]

Hi @rocktheboat (https://www.vwaudiforum.co.uk/forum/member.php?u=259716) ( Crasher ), i have stumbled upon your post while searching the deep dark web for answers to the exact same issue you have described. I have stripped half the car and gone around in circles. Did you ever resolve your issue, id appreciate any help possible. Do you perhaps have any wiring diagrams to help me fault find? TIA

[Crasher]

Remind me of the issue, drank a few bottles in that time.

[KK26]

Hi Crasher

I wrote two long replies but did not end up sending them, then lost the messages :aargh4:

The symtoms were: Flashing on instrument cluster Park brake light and Transmission "PRNDS" and 3 beeps. Radiator fans turn on full speed.

I reached out to rocktheboat and he confirmed his ECU was at fault and was repaired. Car operational since the repair.

My ECU has also taken a dive. I managed to find a second hand unit from a GOLF 5. Plugged in and the symtoms have cleared.

My next step to to try transfer the setting over from Donor to new. I am learning each step of the way and would appreciate your advice. If my EEPROM is still ok, would it be as simple as removing it, reading flash storage (for safe keeping, just in case) then placing it into the new unit? Any code changes needed due to the ECU being from a VW Golf 5 and mine being an Audi A3?

All i have on hand currently is the HEX-V2 module. I am looking at purchasing an EEPROM reader. Any guidance on this if you have any please :beerchug:

[Crasher]

I only do this using the used ECU matching procedure with the dealer system ODIS, working on the ECU’s internals I leave to specialists.