P0481 cooling fan 2 control circuit malfunction

[stevenkeyte]

Was on in the car (2.5 auto, 2005 year) went for a short run and the temp gauge started to climb above the usual 9 o'clock position, I got home and whilst waiting for the car to cool down so I could investigate the 'overheating' further, I scanned the car with TOAF and the only fault was P0481 cooling fan 2 control circuit malfunction (I had replaced the original resistor three years ago for a Jules gold resistor) This was a new error code as I cleared all the codes a short time ago whilst looking at another fault.

After the car had cooled down, I did the demist test and to my surprise the fan came on, specifically, with the key in position two but the engine stopped, no activity from the fan, but with the engine running the fan turns.

I then enables the onboard instrument pack diagnostics and ran test 7.0 observing the temperature, at 100ºC the low speed fan started to operate, but the temperature continued to rise and at about 106ºC the high speed fan began to operate, I abandoned the test when the temperature rose to 109ºC

My personal thoughts are that the thermostat has failed shut - I inspected in the 'V' of the engine and there is no trace of coolant and there has been no loss of coolant confirmed by the coolant level having not changed in the expansion tank.

Any thoughts as to the likely cause of this behaviour?

Regards,

Steve

[SD1too]

Originally Posted by stevenkeyte

My personal thoughts are that the thermostat has failed shut ...

You can check for that eventuality Steve. Once the radiator fan starts running, feel the hose containing the bleed screw. You can find this beside the air cleaner. If it's cold or luke warm, that will confirm your thought.

Originally Posted by stevenkeyte

I scanned the car with TOAF and the only fault was P0481 cooling fan 2 control circuit malfunction ...

As your engine has a 2 speed resistor fan system, that's nothing to worry about. TOAF is reporting that the medium speed isn't working. That's because you don't have one!

Simon

[stevenkeyte]

Hi Simon,
After I posted my initial issue, I thought about checking the 'top hose', it's something I'll do tomorrow, now I'm reasonably certain that there is no issue with the cooling fan operation, as I said, I'm reasonably certain the issue lies with the thermostat, luckily I have a new set which I've had as a spare since I bought the car,

Steve

[SD1too]

Originally Posted by stevenkeyte

... I thought about checking the 'top hose' ...

Actually it's the bottom hose Steve! Our engines have the thermostat not in the flow to the radiator but in the return from it. So the hose I mentioned, with the bleed screw fitted, comes from the bottom of the radiator and delivers coolant to the thermostat.

So, if the thermostat fails to open, as you suspect, there will be no flow through it and the "bottom" hose will remain cold or luke warm. It should feel hot.

Let us know how you get on.

Simon

[stevenkeyte]

Hi Simon,
I've now had the opportunity to have a further look at the cooling issue and as you suggested the bottom hose (i.e. the hose with the bleed screw) is cold throughout the test.
At the start of the test, the ambient air temperature was 22ºC and the indicted coolant temperature was 18ºC (as given by test 7.0 on the onboard instrument pack diagnostics). The engine was started and the temperature was monitored, at 100ºC the fan commenced operating, a check of the bottom hose showed no discernable increase in temperature. I allowed the engine to run until the indicated coolant temperature was 105ºC, again the bottom hose was checked and there was no change in temperature, at this point I concluded testing and switched the engine off.
I am reasonably confident that the temperature sender fitted to the car is functioning correctly, as the coolant temperature at start was only 4ºC less than the air temperature.
My conclusion is that the thermostat has failed shut, or is stuck closed, either way, the next step is to fit a replacement thermostat (I already have one in my 'spares' box).
Regards,

Steve

[SD1too]

Excellent work Steve; I agree with your method and conclusion one hundred per cent!

If you haven't done this before I'd recommend removing the manifold chamber and L.H. bank inlet manifold for full access (as opposed to the keyhole method). This will also minimise the risk of breaking the curved and straight pipes which I recommend that you fit with new genuine 'O' ring seals (available separately, CDU 3858).

You might also need a pair of new serrated clips (PYC 101320) if they cannot be moved within their recesses. After reassembly be sure to move both of these outwards so that they are in intimate contact with the water pump inlet and the thermostat housing, then tighten the jaws firmly. This will ensure that you don't suffer future coolant leaks into the 'V'.

Simon

[stevenkeyte]

Thanks for that Simon, I'll order a couple of the serrated clips for the coolant pipe, for some reason, I don't have any with the new thermostat kit!

Steve