Thread: Disco 3 viscous fan problem

Originally Posted by Sunny coast Chris

Hi All
Was wondering if anyone can tell me how to check the viscous fan motor, if that even possible.
Its on a 2005 4.4 v8 and the fan is running constantly, and the research i've done points to the fan being faulty.
I have checked the connector, the relay and fuse and all seem ok.
The battery light is illuminated on the dash but there are no engine fault codes showing.
From the information i found it sounds like its not just a 12V on/off power supply.
I cant find anything on how to test it, but as they are nearly $600 i thought i would seek some advice first!
Cheers

The fan always runs as it has an amount of viscous drag that keeps it always turning. The electrical connector then allows the fan to increase the bins up so that it can go up to 1:1. It is variable, IIRC variable voltage.

I am also interested to understand how it can be tested but I don’t believe there is a test routine in the GAP. I’ll go and read the manual and see what it says.

Ok. Manual confirmed what I suspected. Based on road speed, coolant temp, engine temp, AC system pressure etc, the electronic element of the fan is used to increase the fan speed. The fan has a speed sensor and based on the voltage sent to it, determines the amount of lockup.

So the ECU knows what RPM it’s aiming for and can sense that as it applies voltage to lock it up. It also detects an open circuit and logs a fault code. Presumably it could also log a fault for the fan not achieving expected RPM, but can’t confirm that.

I think it’s therefore unlikely you have a viscous fan problem without any faults logged, but as I said above, it’s possible if it wasn’t achieving the expected speed for the applied voltage, that this may not be logged and performance reduced

Hi Jeffster.
The way i understand it it works the opposite of an ordinary fan, as in the voltage is applied to the fan clutch to slow the fan speed down, not speed it up.
The problem i have is the fan is running at engine speed all the time as the revs rise so does the fan speed and the noise, so the car sounds like a jet taking off as im driving!
I found threads on some forums describing the same symptoms, some were caused by faulty relays and some were faulty complete fan units.
But i cant find anything on actually testing the fan/clutch unit.
I looked at all the inputs from the engine i could think of that might control the fan, oil temp, coolant temp etc but they all looked ok.

There's a solenoid in the fan clutch which takes the place of the traditional bimetal valve. The clutch has 4 pins. 2 are common high (from fuse 10 in the Engine bay box) via relay R6, one is the solenoid and one is a speed feedback to the ECU.
If you unplug the fan, you get the symptoms you have now, plus errors logged in the ECU. There are no plausibility errors for the fan. So the only thing the ECU knows is if the solenoid line is unplugged (open), shorted high or low.

That makes your particular symptom hard to test, because it's the natural state of the fan if unplugged or undriven by the ECU.

There's no point checking what would normally be seen as "aggravating factors" (temps and pressures) because I've watched all those closely previously and the fan still ramps up. The only thing worth looking at is the fan PWM output (Viscous fan PWM duty cycle) and Fan RPM.

On mine, cold at 1000RPM. With fan duty cycle > 65% fan RPM is ~500. With fan duty cycle < 30% fan RPM is ~1300.

If you were to apply 12V to pin A and gnd to Pin D of the connector on the fan you could test the solenoid, but getting test probes in that close to whirling spinny things isn't something I like the sound of (even though I'd do it myself).

When I start the car cold and let it idle for a bit, the PWM slowly creeps up from 0% to close to 100% and the fan slows down. If I turn the A/C on then as the high side pressure approaches 13Bar the PWM falls and the fan speeds up. That is reproducible for me anyway.

Ahem. Re-reading your first post, you say the battery light on the dash is on?

There should be fault codes stored as that lamp is driven by the dash looking at CAN bus messages.

Originally Posted by BradC

There's a solenoid in the fan clutch which takes the place of the traditional bimetal valve. The clutch has 4 pins. 2 are common high (from fuse 10 in the Engine bay box) via relay R6, one is the solenoid and one is a speed feedback to the ECU.
If you unplug the fan, you get the symptoms you have now, plus errors logged in the ECU. There are no plausibility errors for the fan. So the only thing the ECU knows is if the solenoid line is unplugged (open), shorted high or low.

That makes your particular symptom hard to test, because it's the natural state of the fan if unplugged or undriven by the ECU.

There's no point checking what would normally be seen as "aggravating factors" (temps and pressures) because I've watched all those closely previously and the fan still ramps up. The only thing worth looking at is the fan PWM output (Viscous fan PWM duty cycle) and Fan RPM.

On mine, cold at 1000RPM. With fan duty cycle > 65% fan RPM is ~500. With fan duty cycle < 30% fan RPM is ~1300.

If you were to apply 12V to pin A and gnd to Pin D of the connector on the fan you could test the solenoid, but getting test probes in that close to whirling spinny things isn't something I like the sound of (even though I'd do it myself).

When I start the car cold and let it idle for a bit, the PWM slowly creeps up from 0% to close to 100% and the fan slows down. If I turn the A/C on then as the high side pressure approaches 13Bar the PWM falls and the fan speeds up. That is reproducible for me anyway.

This doesn’t make sense to me as the manual makes the statement that if the fan is unplugged the vehicle will overheat and error will be logged, which to me says the fan is in a “looser” state without power applied.
To quote “if the electrical connections to the viscous fan are disconnected, the fan will idle, and the engine may overheat”

Originally Posted by Sunny coast Chris

Hi Jeffster.
The way i understand it it works the opposite of an ordinary fan, as in the voltage is applied to the fan clutch to slow the fan speed down, not speed it up.
The problem i have is the fan is running at engine speed all the time as the revs rise so does the fan speed and the noise, so the car sounds like a jet taking off as im driving!
I found threads on some forums describing the same symptoms, some were caused by faulty relays and some were faulty complete fan units.
But i cant find anything on actually testing the fan/clutch unit.
I looked at all the inputs from the engine i could think of that might control the fan, oil temp, coolant temp etc but they all looked ok.

See my post above after reading that manual

So today on the way home the battery light went out intermittently and eventually the engine fault message showed up on the dash.
Checked the codes and it showed P0480 Fan 1 control circuit, this is the first time an engine code has shown up since this started, the only codes up till now have been Body Control Module codes which appear unrelated.
Im starting to think the problem isn’t an issue with the fan clutch itself. When I did a reset of the engine fault code the fan slowed down and seemed to gain control for 5-10 seconds then went back to “racing” again. Also I noticed it does the same on start up only slightly quicker.