both cooling fans on with sensor unplugged,help

[steve1ph]

hi, im still having problems with my cooling fans. they will not come on normally (at all). while i was reading through my service manuals checking and trying various things to get them to come on i discovered that both fans will come on and stay on when i start the car with the coolant temp sensor (below the throttle body) unpluged. i plug it back in and the fans go off an not work at all. as yall know the only time both fans would be on is if the a/c is on. but right now mine is not working. im waiting on a new condensor. sound like anything yall have come across? thanks. the car is a `90 .

 

[69MyWay]

stock computer chip, and coolant sensor?

If so, you do realize the fans won't come on until around 230 degrees when not using the a/c.

There is an easy fix.

Go to the fan relays on the driver side of the radiator support. You will find the little green wires going into the relays are the ground signals from the computer to trigger the fan. Splice in a hard ground to the frame, and the fans will run as soon as you turn on the key, regardless of temp.

My guess is you have a bad computer.

 

[Top]

Better would be to put a toggle switch in your dash somewhere between the hard ground Chris suggests and the relay. Then you can watch the temp and switch the fans on after the T'stat opens. No reason to run the fans before your T'stat opens. Just wear and tear on them.

Good luck

 

[Magmotor]

What you've described is perfectly normal operation for the ECM & fans. <see pic>
If the main fan won't come on after 224 degrees or so then the 'temp cooling switch' needs to be replaced, not the 'temp sensor'. If that doesn't solve the problem then the 'relays' are next: if not that, then the ECM needs to be checked for AC Request and Fan Request.

 

[steve1ph]

thanks

i think the first paragraph applies to me more so than the others. cause with the sensor unplugged which mine is the ecm is thinking bad sensor hence the fans on all the time. so im going to buy a coolant temp sensor and get back with yall.

 

[steve1ph]

xmay on that idea. if the sensor is bad then the ecm would turn them on any way. which is not doing with it plugged in.

 

[rrhayden]

The best way to check the operation is to jump the diagnostic connector. With the key off jump it like you are reading a code, then turn the key to the on position do not start it. Both fans should come on.

If they do the system is working fine. If not it sounds like the ecm because as you say both fans run with the sender un-pluged. This indicated the relay and fan have power and ground.

 

[C4ME]

What you've described is perfectly normal operation for the ECM & fans. <see pic>
If the main fan won't come on after 224 degrees or so then the 'temp cooling switch' needs to be replaced, not the 'temp sensor'. If that doesn't solve the problem then the 'relays' are next: if not that, then the ECM needs to be checked for AC Request and Fan Request.

OK I have a Fan Request flag indication on my car...What does that mean?

Thanks.
Joe

 

[Vettefan87]

Have you ran the car to about 225 to 230 degrees to see if the one fan comes one? That is the normal factory turn on setting for the fan, then the auxilliary fan kicks on at like 245. Good Luck


Justin

 

[C4ME]

Have you ran the car to about 225 to 230 degrees to see if the one fan comes one? That is the normal factory turn on setting for the fan, then the auxilliary fan kicks on at like 245. Good Luck


Justin

My problem is that the fan is on when I turn the key and does not go off. I had some odd wiring that had been done and have removed that along with replacing the relay which was our original diag. Still fan always on. So, I used my handy scanning software and noted that there is a perpetual fan request with the temp sitting at ~ 140 as the car heated up. I am thinking the fan request being set means that the coolent switch on the starboard side (right side to you non-sailors) is kaput. Not sure, as I have not gone out into the cold garage to complete the troubleshooting, but was just thinking out load.

Joe