There are high and low speed fan relays in the underhood fuse/relay center. They are turned on and off by the PCM.
For some reason a relay may be shorted on or the PCM is getting wrong information about engine temperature or if the A/C-defrost is on or the PCM itself may have an issue. Any 'ck eng' light on or fault codes?
Sometimes the contacts stick, they weld together from internal arcing as the contacts open. Usually you can cycle them to unstick them. Then replace or swap relays underhood that have the same part number.
It could if it was a signal value out of the high/low range that the PCM allows, like an open circuit or short to ground. If it is still within a 'believable' or valid temperature value to the PCM, it shouldn't set the 'ck eng' light.
If a rad fan relay is pulled out with the ign on, it may set a code as the PCM sees an open circuit to the relay actuator coil.
I am puzzled by this. Both fans are coming on and I swapped around the relays with no success..Could there be another part of the circuit that is stuck open?
Also thought it may be the Engine coolant sensor. Does anyone have specs on what the resistance reading should be for this sensor. Not sure how to test it..If this is malfunctioning, could it give the wrong signal to the computer?
If it were the CTS, you should get a fault code. Nevertheless, the CTS is a steep negative-slope thermistor. Very approximate values would be: 15K to 22K ohms at about 25F to 30F ambient; 3K around 70F ambient; and with engine fully warm, about 600 ohms (as fast as you can shut the engine off and unplug the sensor to read it, the resistance will climb to over 1.3K).
Thanks everyone again, will try pulling the relays while the fan is running..
Interesting thing happened..Started car this morning and the fans did not come on. The temperature has warmed up about 10 degrees so I wonder if the relays have a threshold temperature before they stick?