electric fan not getting power

A couple of days ago the idler pulley bearing seized and the pulley shattered, causing the belt to come off. The engine overheated pretty quick, and I did not notice the electric fan coming on. Today I got under the hood for some other stuff and tested this stuff while I was there.

If I turn on the AC or Defrost, the fan does not spin up. I put a voltmeter on the fan pins and got no voltage either. If I apply 12v directly to the fan (wires to the battery) then the fan spins up fine. So it would seem that the problem is that the electric fan is not getting any power from the plug.

I looked around but could not see where the fan wires come from. Any pointers?

Thanks

I read the relevant parts of the cooling chapter in the FSM and it says the fan is supposed to come on when the temperature hits 190 F, which is not happening.

It also said there was a relay in the power distribution center, so I went and looked there. The relay is identical to the A/C and starter relays, so I swapped them all around and all that stuff still works so the relay appears good. The FSM also says that a bad relay would kick a trouble code that could be pulled with the key trick, and there are no codes. There was also a 30 amp fuse in the PDC for the fan, and it also tests good with a test light.

At this point I need to see if the relay is getting 12v input, I suppose. I'm not a relay guru so any suggestions on ways I can test if the relay is getting signal and producing output would be appreciated.

|
- -
-

The relay plug should look kinda like that. The vertical slot and the bottom most slot are the ones that get switched off/on. So if you jumper those the fan should run if the socket is getting power. The far left and right pins from the vertical slot are the ones that control the relay. One pin would be positive and the other negative when the computer calls for the fan to turn on.

Slo-Sho said:

|
- -
-

The relay plug should look kinda like that. The vertical slot and the bottom most slot are the ones that get switched off/on. So if you jumper those the fan should run if the socket is getting power. The far left and right pins from the vertical slot are the ones that control the relay. One pin would be positive and the other negative when the computer calls for the fan to turn on.

Click to expand...

It's a 5-pin relay

I measured voltage on the outside lateral pair and got a constant .02

The middle pin is not used in this application. If the engine temp is hot enough for the computer to energize the relay and you are not getting power at terminals 85 and 86 (outside lateral pr.) then I would look into replacing the temperature sending unit located in the thermostat housing. Did you verify that you have constant power at the socket?

My bet would be on the temp sensor.

Depending on your year model you may have 2. One controls the gauge and one controls the fan and other fun stuff. One is on the head near the back and one is usually (Once again - depending on the year) screwed into the thermostat housing. Both can be had for around 10-20 bucks at the parts store.


(Darn Slo beat me to it... ) lol

It's not the temp sensor, since I have also tested the fan control logic by turning on the AC and defrost and the fan circuit does not get power then either. Anyway I replaced the temp sensor last year to address a constant code 21 ("too cool for too long") and the replacement sensor appears to be working (no other errors), but again that is not the problem point since the fan circuit gets power from the ECU and/or the AC compressor relay.

I am getting constant .02V ("point zero two") at the relay input so it seems the circuit is torn up

Here is some interesting reading, although I think it is about Renix wiring -- http://jeephorizons.com/phpbb/viewtopic.php?p=71583#71583

I should probably remove the PDC and probe for signal back there

Is there main power at the socket? Can you jumper the 87 and 30 pins to make the fan run?

Slo-Sho said:

Is there main power at the socket? Can you jumper the 87 and 30 pins to make the fan run?

Click to expand...

Yes to both questions. I just went out and ran a wire between those plug posts and the fan spun up. I also stopped by the shop that does the electrical and AC work on my Cadillac and talked to the mechanic there, and he hooked up a test light and got power. However his second test light hookup failed. His guess is that there is a ground fault which is preventing the relay from being fired, since the AC relay and ECM both fail to trigger. I interrupted him so I don't know if he was really thinking about it.

You're going to have to find out if the computer sends a - or + 12v to the relay to trigger it.

Has this problem been fixed? I am experiencing the same thing after installing a late model cooling fan I got off Ebay. It seems to pull considerabley more amps than my square bladed fan on my 91 comanche. I am concerned that the fan motor may have a problem causing this higher draw. I intend to do the circuit checks suggested but would love to know what you found out.

higher amps could mean its a higher horse motor, which is ok if ur fuse AND relay will handle it, or it could be faulty and drawing high amps due to drag. although im not a mechanic

A few days after posting, the fan came on when the gauge got up to about 235 while idling in hot weather. Then it started coming on more frequently. I did not do anything to fix it, it just fixed itself. I suspect the relay contacts were dirty.