I have an 02 MCS, with the resistor modification that has worked perfect for several years. Last week the radiator fan quit working and fortunately I caught the temp gauge just as it started to rise. After the car cooled off I was able to drive it without the a/c running and the engine ran normal temp between 86-96C, based on the test mode reading of the water temp.

I checked the resistor and it was still ok and all of the fuses for the fan were fine. I swapped the fan relay with another same rated relay and had the same result no fan. Today I replaced the radiator fan and buttoned the car back up thinking the issue was solved......no radiator fan with or without the a/c running. At 106C no fan action. At this point I'm rulling out the fan assembly and the resistor.

Anyone know where the water temp sending unit is that triggers the coolant fan? I was assuming that it was ok being that in the test mode I can read the water temp. Apparently I was wrong on my assumption.

Any other suggestions are welcome.

 

Check the fan fuses & relays. Make sure swapped relay not only has same rating, but same diagram & part number. If you're reading from the test mode, ecu s getting the feed from the coolant temp sensor near the thermostat. So, chances of sensor not feeding isn't so high.
On a likely unrelated issue, when you bypassed the dead resistor, did you jump that lil' thermistor/diode in series w/ that huge green resistor? That fails on your low, too.

 

When I installed the heavy duty resistor, the diode was fine. Yesterday I installed a whole new fan assembly with the large green resistor. I took my resistor out until I need it in the future.

I also checked the relay that I swapped and all numbers match including the inked numbers printed on the top.

 

Don't think the diode is prone to failure, but actually don't really know what the diode is
really there for (?prevent back-emf spike to the relay when fan cuts on/off?).

 

From reading about our fans in UK boards a while back, that diode is said to be a thermistor. What it's there for is a mystery. Current flows 1 way through that resistor circuit & I can't figure why a diode is needed there.
Believe it or not, mine actually failed. Having the 2-plug, you can imagine the hassle of doing 2x the entire jump process. Now both hi & lo are back.

 

Having a thermistor in parallel with a 0.33 ohm resistor makes absolutely no sense
from an electrical standpoint.

 

^That too. So, anyone who can accurately verify the use & specs of that diode or thermistor, please share.

 

Great conversation on the diode, but that's not the issue here.

What triggers the fan? And if I'm getting a good water temp reading when I'm in the computer's service mode, does that rule out the temp sending unit?

 

I'm thinkin' fuses, connections, ground?.... as you're not getting power to your fan once it's supposed to be called. I think you already know how our cooling system works. Here's a refresher:

Thermostat begins to open at 89-92° C (192° F - 198° F) and is fully open at 103° C (217° F).

Expansion Tank Cap Cap pressurizes the system to 1.1 bar (16 psi) at which point the cap valve will lift to relieve pressure.

Cooling Fan

Radiator Fan is a nine bladed fan measuring 400mm in diameter, driven by a 350 watt motor controlled by the EMS2000.

Low speed is switched on at 105°C (221° F) coolant temp and off when the temperature drops to 101°C (214° F).

High speed is switched on at 112° C (234° F) and remains on until the system coolant temperature drops by 4° C (7.2° F, so around 227F) at which point the system will revert to Low Speed.

The cooling fan will also operate on Low Speed when the Air Conditioning is switched on and system pressure reaches 8 bar (116 psi). Should the Air Conditioning system pressure rise to 18 bar (261 psi), the fan will automatically run on the High Speed. Just make sure your A/C is functioning properly w/ enough refrigerant to create the ideal pressures.

If all else fails, why not wire it up w/ a fused manual switch on HIGH always?

 

Well I'm ashamed to say the problem was a small 5 amp fuse in the engine compartment. I checked all fuses with the fan markings but didn't check the other fuses. This one has an "engine block with a lightning bolt" as the designator.

Well now I have a new fan assembly and a 5 amp fuse

John

 

Keep an eye on that fuse....it is SHARED with the PS pump fan if I recall right....so if the PS fan gets stuck...grit in the bearings, a plastic bag, etc...the fuse will blow....leaving BOTH fans inop.
The PS pump is about a $600 item...so KNOWING the cooling fan is out is IMPORTANT!!
And Like I posted BEFORE in another thread on this with you(I think), MINI changed the wiring in 2005...and there are a PDF around on how to do the mod to split the wiring to prevent this from happening again....many cars were changed by MINI if they were under warranty when the change occurred.

 

2nd what Zippy said. Your symptoms simply pointed to power source. & Zip, if you have links to the PS fan re-wire, I'd appreciate it much. I have the 2-plug fan where the PS fan goes w/ the high.