[CudaPete]

Most likely the fan relay.

 

[ImperialCrown]

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?

 

[msg123456]

Thank-you both for your replies..No codes or lights yet. Is the fan relay located in the fusebox under the hood?

 

[ImperialCrown]

Yes and their locations (high speed relay and low speed relay) should be labeled under the lid or next to the relay itself.

 

[Bob Lincoln]

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.

 

[msg123456]

Thanks again everyone..I guess a relay failure would not give a fault code would it?

 

[msg123456]

Would I get a check engine signal if my engine coolant sensor was causing the problem?

 

[ImperialCrown]

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.

 

[chuzz]

You can swap the relays around and see if that's it. They're all the same number.

 

[msg123456]

Hi All,

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?

Thanks.

 

[Bob Lincoln]

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).

 

[ImperialCrown]

Both fans do run in the low or high speed mode. They are 2-speed fan motors.
If you pull a relay and the fans stop, that is the circuit (low or high speed) that is staying on.

 

[msg123456]

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?

 

[Bob Lincoln]

Not temperature. It's the kickback current that welds the contacts together, and eventually the stresses relax and the contacts break open again.

 

[msg123456]

Thanks again Bob,

I think I may as well replace both relays and see how that goes.

Appreciate everyones help.

 

[ImperialCrown]

For diagnostic purposes, it would be OK to swap the 2 relays with a couple of 'non-critical' adjacent relays of the same part number in the fuse/relay center.

 

[msg123456]

Sounds good, thanks Imperial.

Happy New year everyone