Hi all, Before I go and start spending a fortune on parts I just wanted to put my problem out there, to see of any one had come arcoss it.
My 2005 GT has no cooling fans working, or sometimes one very very slowly. I have put it on VCDS and there are No faults related to cooling system and when I run the fans through VCDS they still either run slow slow or not at all (rocking) and still no fault code. The car is new to me and there is nothing in the History about cooling issues. My air con needs a re-gas I know but I can drive around all day. But hit slow traffic and the gauge goes to red quickly and I have to find some open road to cool her off.

Any thoughts or advice would be gratefully received (as long as it is not "sell Her" as I am in LOVE).

Thank you. mcs elec

 

Hello - These fan motors are high draw (30/40 amps @ full speed). Depending on how much they've been used in almost 15 years now (2005MY), and how much "elements" they've been exposed to, it might be that they're shot. If you can get to the fan pigtail, apply 12v directly to the fans, see if they still run slowly. If so, the fans are gone.

If they suddenly breathe life, then you'll need to look upstream. There will be a fan control module next in line. It is nothing more than a digital (sophisticated) relay and pulse rheostat. On the low voltage side it is usually 5v feeding the relays which switch 12v (high amp and heavy wire) to the fans. The ECU sends pulses on the 5v side at variable frequencies to produce a fan speed measured as a % of full speed. These fan control modules are transistorized, they get hot and burn up, so the FCM does get tired and "goes south".

Either of the above reasons could account for the continuously slow fan speed. A third possibility is grounding. If the earth side of the circuit has lost integrity, then essentially could end up with the same high resistance outcome.

As long as the ECU is producing the 5v pulses according to its MAP, and the ECT remains within an expected range, then there will be no codes shown in VCDS. I'll guess this problem has arisen while ambient air temps have remained cool. If, however, you reach Ambients more in the 25*C range and above, the ECT will cross a threshold and set a CEL.

My (wild) guess is FCM.

 

The fan control modules (one for each fan) are the silver boxes with the cooling fins. Your cooling fans should look like these. I believe Bentley used this same cooling system on 2004 to at least 2010:

 

Thank you so much for the information. I think it will be really helpful. I think I can see one supply to a Fan from up top.
Do you a standard PWM tester might be able to check out the FCM if I give I it 12v on the large wires 60amp supply and then use the PWM to give it 5v PWM .

I saw elsewhere that some of the Audi fan controllers are the same and interchangeable. Have you come across that?

Thanks again really helpful info.

 

Hope this can help also.

 

I would caution you STRONGLY not to "ping" the 5v. I am not sure here, but for a lot of these same systems the signal is actually a ground and not a +5v. In other words, the + supply is permanent, and the ECU signal completes a ground; therefore, you don't want to be pinging that signal on its earth side with a +v. The easiest half test of this circuit is just unplug at the FCM, bypass it, then feed +12V directly onto the fan motor leads for a short moment. If the fan runs full speed (like it is NOT doing now), then the fans are good. If you can verify the earth is good (it is often the closest/shortest grounding lug in the engine compartment), it leaves the FCM as the culprit.

On the low voltage signals, I have found bad wires on other model cars, but if the LV signal failed there would be a fault code set.

Regards the Audi crossover, cannot say for sure, but 99% sure the Audi or VW Phaeton FCMs are going to be crossovers.

 

Wow we posted at exactly the same time! And a good find! Well done!!

 

Just trying to help out when I can! I just need to sell this 750 so I can get some more goodies for Jade!!

 

If you want to take care of a quick check that is free - the two grounds for the fans are found on a single ground lug. They are G00081 (fan 1) and G00082 (fan 2). You'll have to hunt for the lug. The ground wires are brown and this diagram is for a RHD. Make sure you have a clean tight connection with wires in good condition.

 

Thank you so much for the Video, I am formulating a plan and I will keep the post updated .
Thanks again

 

Bwings, amazing info , thank you again . I have a plan now, I won’t test the FCM units, I have however found two working S/H Phaeton units for very little £££ so I have ordered and next weekend I will strip and test fans and one way or another I hope I will have all the parts to sort the problem I Checked Earths and all seems secure and corrosion free. I will of course update to the post when job is done. Thanks for the help , invaluable. MCS Elec

 

Hi all, just to add to this post and ask a bit more help, I have now found upon more detailed check that I have a current/voltage supply issue. The row of 50 fuses in the engine fuse box for fans/ air con and air pumps are showing 12v to 11.4v with engine off and nothing working, when I start vehicle the voltage drops down to 3volt or less then 0v. I obviously have a bad connection or damaged wire some where. The wiring that supplies those fuses is Red/brown stripe. But the online manual has no wiring coding, more of a parts list so I have no idea where to start, apart from engine fuse box and try to trace. Does anyone know of a common problem around this area. Or does anyone have a coloured code diagram so I can have a head start to trace this Red/brown back to where it is Good. Thanks for reading my rambling message for help.
Mcs elec

 

Look carefully what’s lying at the bottom , running through.I suspect it’s an aftermarket mod to run those wires and connectors off the scuttle floor which is under that unit
So now they keep bone dry .



The red dot is amazing, actually allows water to drip / flood the fuse box lid !! - how ridiculous?


It’s a “ common problem “ , indeed imho the route of all evil with theses cars due to water ingress .
Three levels
1- blocked scuttle drain
2- exposed fuse box to weather ,
3 - poor reseating and poor fusebox seal

1- One ,if not the main harness runs on the floor of the scuttle and under the HVAC , so it’s can get wet and corroded.easily with blocked drains .Many of the early cars had a mod done like in the pic above , a “splice “ and repositioning higher of this harness .

2- The lid of the box is flat water can settle on top .Those multiple pin plugs are sat on raised supports / clips but exposed to direct water splash - rain , snow melt , car wash , road spray etc etc.

3 - Fuse box lid is difficult to properly exactly reseat .If so how do you really know it’s actually water proof ?

Outside parking on other than flat flat surfaces obviously changes the water pooling ability.Ie if the car is tilted towards a corner because the centre drain ( even if it’s clear ) is relatively higher water will pool in the scuttle and slosh about next time you corner .

Most cars have drains in the scuttle corners easy to access and water from the wind screen just runs straight out .
Most cars engine compartment fuse box are NOT exposed to the elements AND better lidded and sealed , and there’s NO water drain above them .

rant over

https://www.6speedonline.com/forums/...enance-gt.html

I,am sorry I can’t help with the tech info re wires Bwings will be along soon .

I think mine (2003 launch modal ) has had by now a splice done .They reposition the main harness higher off the scuttle floor and through the HVAC air in .You might to able to see it in the pic above .

 

Right with you John.

 

Hi all, right I have found my culprit (photos attached). John I am in total agreement it is a Very very poor idea, from very very poor design. They are in Crewe for goddess sake. They have trees and get lots of rain, unless autumn got cancelled up there so leaves don’t fall off trees. How did they not think it through. Anyway I am attempting repair with out complete strip of HVAC unit. We shall see, if not I am off to Crewe to the R&D department with a pair of my home made ******** removers.