# Relay Diagram



## Kofita (Jul 8, 2018)

Hello guys.

Continuing from my last thread. Replaced my thermostat coolant temp sens, fuse box, fan temp switch and the fan relay. My front fans still come on 100% if I put the coolant fan fuse in.

I tried to look under the steering wheel at the panel of relays in hopes to find another one there that could be broke but I've searched far and wide but can't find a diagram of the relay panel.

Does anyone have one or a picture of theirs? It's a 2001 225 Coupe.

Thanks guys!


----------



## PlasticMac (Apr 25, 2017)

Kofita said:


> Hello guys.
> 
> Continuing from my last thread. Replaced my thermostat coolant temp sens, fuse box, fan temp switch and the fan relay. My front fans still come on 100% if I put the coolant fan fuse in.
> 
> ...


Does this help? Looks like it maybe the Coolant Fan Control Module. Control seems to be solid state not relays. 
Mac.


----------



## Pukmeister (Dec 27, 2017)

According to repair manuals there are no relays for the cooling fan electrics.










Red/white wire powers low speed fan operation (via resistors) either from fan controller module output or radiator thermo switch (dashed lines in diagram).

Red/black wire powers high speed fan operation (no resistors) direct from fan controller module output.

Radiator thermo switch (Red/Yellow) provides a run signal for fan controller module to run fans at 100%.

I think if fans are stuck at 100% you need to probe for 12v output signal (Red/Yellow)from thermo switch to fan controller. If 12v present when cold then thermo switch is faulty. If no volts then I would assume fan controller module is faulty and providing unwanted power to fans.

Maybe pull the radiator thermo switch connector and see if fans stop ?

Reading your OP and seeing what you have replaced, something doesn't add up. Have you had an a/c gas recharge lately ? High pressure if overgassed might call for full fan speed to reduce a/c gas pressure. Either that or you may have a permanent 12v feed spliced-in somewhere in the wiring by a previous owner to bodge the fans to stay on.


----------



## PlasticMac (Apr 25, 2017)

As far as I can see, the fans are switched, using solid state "relays" which are integrated into the Fan Control Module "FCM", no electro mechanical relays involved. The radiator "thermal switch" is not a switch as such, it just sends a signal (by opening and closing), to the FCM. Mac.


----------



## PlasticMac (Apr 25, 2017)

After the fuse checks, I'd go for the connectors on the FCM, unplug them, check the contacts are clean and bright. Mac.


----------



## silkman (Jul 29, 2004)

The fan relays in the TT are in the fan controller box under the battery. Its a single sealed unit.


----------



## Kofita (Jul 8, 2018)

Bless you all for the replies.

After unplugging the thermal switch the fans still stay on so yes I assume a constant 12v current is running. He also installed the radio in a stupid way only found out after it drained my battery so this doesn't surprise me.

Changed everything I can in this circuit so now I'm waiting for an electrician to come and take a look.

Another issue is that even after installing my new coolant temp sensor my CC is showing 121 degrees but the ecu is receding the right coolant temp because I have a liquid boost gauge that shows me the correct temp. Is it possible that the coolant temp sensor is only giving out one correct reading or do we think that somethings wrong with the connection from the coolant temp sensor to the CC

Thanks once again guys!


----------



## Pukmeister (Dec 27, 2017)

Its sounding like somebody has frigged the run signal for the fan controller, causing it to force-run the fans all the time. Either that or you have a live short on the run signal or a faulty controller. A good electrician should be able to trace the wiring, probe for voltages and determine for certain what is happening.

If your liquid gauge shows the true temperature but the climate control does not, and assuming they share the same signal, I suspect somebody has been messing with the wiring to the climate module or it has a high resistance wiring connection (perhaps a poor or corroded termination)that is altering the analogue value from the sensor and thus fooling it into reading high, assuming a positive temperature coefficient transducer is used (higher resistance = higher heat reading).

Keep us posted with how things develop.


----------



## Kofita (Jul 8, 2018)

So you guys asked me to update you!

Rechecked everything still the same problem. Went to get my dash fixed. I was 100% certain the dash had nothing to do with the whole issue since the dash doesn't control the fans. Turns out that there was a short in the temp sensor that caused the CC and dash to say the car is at 121 degrees. The dash pod and fan control module aren't linked however the dash and ecu is. The dash sent a signal to the ecu that the car wa supposedly at 121 and the ecu overwrote all other sensors and put the fans on 100%

Now that the temps are back to where they should the fans turn on and off. 
You might know Patrick (totalelectronics) he was a great help and said that he's never seen something like this before. But yeah once again thank you all for the replies.


----------



## Hoggy (May 8, 2002)

Hi Kofita, Pleased it's sorted but if you had used an OEM coolant sensor it may have been solved long ago.  :wink: 
I know a dashpod fault can cause incorrect Code 49/coolant temps reading (Wak had it) but strange how coolant sensor faulty feed to the ECU caused the fans to run.
Always something new to learn with Audi systems.Vorsprung durch Technik
Hoggy.


----------



## Pukmeister (Dec 27, 2017)

Nice one, thanks for the feedback.

Your fault condition sounds like a rare occurrence but now its recorded in the forum the knowledge is shared and any future owners with the same symptoms will now have an idea how to solve it.


----------



## PlasticMac (Apr 25, 2017)

Looking at the circuit diagrams, there is a direct link between the dashpod and the Fan Control Module. The output from the AC, to the FCM is also connected directly, violet/yellow wire, to the instrument cluster "outside temperature display" circuit. I'm guessing that the same circuit deal with coolant temperature too. VDT indeed. Mac


----------

