My 2003 S2K's radiator fan is not turning on, making the car begin to overheat while standing still. I have the modifry ect mod, and while idling in traffic it will sometimes hit 5 bars, indicating 220°.

If you put the AC on, both fans turn on.

I shorted the fan switch relay with a small wire and that made the fan turn on, which makes me think the fan relay is good? I also swapped the fan and ac condenser relays to see if the issue persisted, and it does.

Put a new Fan switch in, and the issue is still happening. What could it be?

 

My diagnosis seems to point to the new switch being bad, if shorting the plug turns the fans on. Is there any way to test the switch without draining the fluid? Is there a way to use a voltmeter to test the old switch in boiling water? I can't find any resistance charts for the switch online.

 

Is the car actually overheating or is the gauge just reading high after you did the modification? These are On/Off switches that read 0 ohms or infinite ohms. I think my AP2 fans come on about 215°F which is in the 8-bar range on my gauges.

-- Chuck

 

The Modifry ECT mod changes the mapping of the stock gauge readout. 4 Bars indicates 205º and 5 bars indicates 220º. When 5 bars light up, the fans are not running. The fans should be running by this point I believe, info on S2Ki points to them coming on around 210º. And when driving the car, it runs at a steady 3-4 bars, anywhere between 180-205. When stopped for extended periods of time is when it starts to climb.

When resistance testing the old switch it was at 0 ohms at ambient temp. I can try throwing it in boiling water and checking the resistance I suppose, to rule out if the old switch was even bad in the first place?

 

Is the car actually overheating or is the gauge just reading high after you did the modification?

Normal range is 160° to 235°. 3 to 4 bars on the AP1 panel.

-- Chuck

 

The switch should read open circuit (high resistance) at ambient. Once it reaches 199F, it should be a short (0 ohms in theory).

To Chuck S' comment, my car never got to 220F nominal operating temp. Once the fans kicked in at 195-200F, the temps quickly dropped to 185F.

 

Hey Chuck,

Not really understanding the issue here. The fans should be on, and they're not.

99SH, thanks I'll have to do some testing, I'm leaning towards a bad replacement sensor.

 

Did some more trouble shooting. I put the old switch that I removed in boiling water, tested with a multimeter and the old switch does in fact work. I suppose the next step is to hit the upper radiator hose with an infrared temp gun and compare to the readings the OBD port is putting out?

Could the issue possibly be with the ECU, if the coolant temp is in fact displaying correctly, but the fan is still not turning on?

 

Have you done any coolant flushes lately? I was going to suggest burping the system (if there's air trapped) or you have a sticky thermostat.

 

Did a coolant flush when I replaced the switch, but the issue had been around before that. Car can run on track without any issues, it's when the car stops that it's a problem, so thermostat should be good.