I cannot say for certain on VAG, but on most of these systems, the ECU signal is completing a ground (not a +5v), so you need to be aware, not to feed the signal with a +v. For the fans, they need to be powered +12v full time (only way they can run ignition off). Jumpering the two heavy cables in the harness going to the fans complete the circuit and what is being switched in the FCMs. If the fan motors are OK they should run with direct 12v.

If the fan motors turn, there are only three other possibilities:
1. Bad FCM
2. Bad, defective wiring, fan grounding especially check for a bad signal wire back to the ECUs.
3. Bad ECU

 

So todays update as follows:

Replaced a blown fuse 12 in the engine bay fuse box - it's a 10A that controls the Rad Fans although i'm not sure which specific aspect of the system it is protecting.

Once that had been replaced, the fans began to function as expected increasing in speed with radiator outlet temperature / engine coolant temperature. The duty cycle and fan speed also increased as expected with the AC turned on. Left the car idle for around 40 minutes and fans were doing a great job of keeping the ECT at around 93/94 degrees C.

Problem is, I am now back to the original fault. After i had performed the above test, i turned of the ignition and locked the car. it was 9 minutes later that the fans started up and continued to run at full speed for about 20 seconds.

So, something is causing the fans to trip in well after the engine is shut down and the ignition turned off. And something also blew the fuse 10A fuse 12.

Latest VCDS scan attached, but doesn’t show anything i would consider t be linked or significant.

 

If you're using the car, do another scan. See if anything returns, especially the U-code. I kinda disagreed with you on your post #14. Deleting a bunch of codes assuming they're a result of a low battery is not what I would have concluded, but if you understand what U-Codes govern, you're describing a recurring issue that is on the lines of a data intermittent failure(s). An intermittent code (failure) especially something like a CanBus intermittent might not immediately reappear; instead, might take certain conditions or a combination. I'm betting you haven't seen the end of the U-code.

 

Here is a suggestion for you.

Earlier it was discussed to examine the integrity of the electronics surrounding the ECUs, including connections and the engine fuse panel.

Take a look especially at the fusebox. See if there is evidence of water ingress (even if dry now).

Check the following:

Relays:
33 - EMS Current Circuit #1
35 - Ignition
38 - Engine Management System Accessories
40 - EMS Current Circuit #2

Finally, the large smoothing capacitor #34. This capacitor (as capacitors do) holds/stores a charge. and is used in battery management in the Bentley. it smooths out voltage ripple between the alternator and the main battery. Without this capacitor (in the event it fails), the ripples can lead to electrical faults.

Any of these components, if failed, MIGHT be causing your fan restart after ignition shutdown.

 

Neil , iam with Bwings on the engine fuse box susceptibility to damp and the route of all evil with these cars .
Like most newbys on here I did find this forum informative and figured out the whole scuttle thing was a problem easy to sleepwalk into .
Mines garaged when I can but it’s exposed in the winter to alpine weather , snow etc often when parked outside that needs clearing .
Wheres it gonna go ? Where’s the melt gonna go ?
I did a thread recently on “ scuttle drains maintenance “

i,am on my third year now and early on I had a minor issue that necessitated removal of the fuse box cover in the scuttle .
I was shocked how exposed it was , those multi pin connections sat on top totally exposed and crucially the flat top nature of the lid .
what I mean is water could ,depending on the parking angle / gradient of the car basically run back , to the side , any direction and if unlucky find in a Sod’s law way any poor lid seal .
lets face it the lid and it’s seal are flaky at best and there’s a knack to properly replacing it .
How do you really know it’s water tight ?

So with a bit of fire proof cloth that easily adapts I cable tied a cover to keep it dry , give it some weather protection .


Tie wrapped .

Scuttle cover in place


The main ECUs are tucked right under and I feel have adequate weather protection from rain / snow melt unlike the “ fuse “ box and the multi pin connect s sat on top .

 

Which begs the Question , Neil is your car or has it been parked outside ?
And if so what gradient if any ?

 

Red circle is a drain + Thx Bentley The bigger blue arrows are potentially where water can get in and errr fall directly on the fuse box , Thx again Bentley.

My cover protects this area from damp .

 

Yes the car is parked outside, on flat ground. When i opened that fusebox yesterday there was no evidence of any current or historic water ingress. The scuttle gets cleaned every time the car is serviced.

However, I will recheck it as soon as time permits. But for now my primary route of investigation is in relation to the following fault on the CAN Gateway:

1 Fault Found:
00470 - Company Comfort Databus in Single Wire
012 - Electrical Fault in Circuit

It would seem the CAN twisted pair is broken somewhere in the car, possibly between the CAN Gateway and the Wiper Control Module (similar fault there). i'll also check to the door modules as this seems to be a common place for wires to break. This broken CAN wire can result in modules not sleeping, and if ECU isn't asleep then it 'could' turn the fans on. Or is that too much of a stretch?

 

On an 00470 and a 2005/06 MY, the driver's door module was a common culprit. They were supposed to have been better after that, but the door module might be the module waking back up again after shutdown. Still awfully strange it would cause cooling fans to run, but based on what else it wakes up.....It's possible the ECUs come back online when the door wakes, and engine temps will definitely be above 107*C if the engine ran to op temps just 5/7 mins before....a bunch of "if/thens" but worth some investigation. Go in and isolate it, clear codes, go through the routine again, see if 470 comes back w/o the DS door module online.

 

I've only had my 2004 for 3 weeks and this may not be related to the OP's problem but mine only come on when the front bumper is off and the bumper wiring is unplugged ( parking sensors and outside temp sensor).

also whenever I write a car related part on my posts on this site the word turns blue and creates a link. Any ideas as to why? This has just happened when I wrote the 3 letter word starting with F middle letter A and last letter N !!!??

 

The site moderator is aware of the problem. As I write this certain words are still turning blue, I shall have to describe the part or function of the car until the site bugs are fixed. A shame as it meant my previous build repair thread about my Copart purchase had to be deleted.

 

Back to 00470 -

Neil - I want to mention that 00470 is a generic canbus fault (U-code). Even though a defective door module often created a 00470 on early MYs (basically, it ran on only one wire), any other system can do the same thing. Actually a very common 00470 is a wire break, and that can be anywhere. On Bentley, several wire breaks occurred at the harness that transitioned at the door hinge, going to the DS door module. I know of one situation where a shorted headlight washer harness caused it.

You mentioned the wiper control module, so you might know something that is sending you in that direction. Usually a clue is another code that is more specific and repeats with the 00470.

Good luck with it. I hope you report back the solution. Great forum data, albeit at your expense right now.

Best,

Steve

 

I certainly will report back - nothing worse that people investing time to help, and then the solution not being shared back

The only only module with a persistent CANBUS error is the wiper module. The wiper module on my RHD is under the scuttle behind the dash very close to the drivers door. From what i can see on the wiring diagrams, there is a direct CAN connection from the drivers door module to the wiper module. So a break in the door shut/hinge area is the first place i will investigate. But otherwise it will be a process of elimination, disconnecting comfort modules until the error goes away. Then traces the wires between the CAN gateway and that module to find a break.

Then, hopefully, fixing that error will also sort the fan problem. If it doesn't, well then i've fixed an unrelated fault - which is still progress

 

Yes, I think you're on the right track. And yes, the wiper motor and mechanism should be just forward of the driver's position and it is quite simple. I've had mine out w/o any tools. Give any cabling a good hard look Neil. If this popped up out of nowhere, then it could be either a bad/defective CanBus module, or a harness with a broken wire. Hope you solve it and would love to hear you're running again!

 

Have you fixed the problem yet? Is it the CAN gateway?