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Old 06-15-2016, 03:17 PM   #1
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Unhappy I really need advice for these cooling fans

1990 cutlass supreme..NO cooling fans at all.

They both have power, i hooked them up to battery and they come on with no issues.

AC does not work, compressor does not kick on.

I have replaced fuses and relays

replaced Coolant Temp Sensor

replace engine temp sensor

Still no luck....wiring looks fine, no cuts or burns anywhere.

At a loss for ideas here, I live in las vegas and its going to be 110 this week so i need some sort of cooling, i really dont want to hook up a toggle switch to turn them on and off. Any suggestions on what else could be causing this?
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Old 06-15-2016, 10:19 PM   #2
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Well, disconnect the harness to the coolant temp sensor(one yellow wire and one black wire in the harness)....turn key to on.....with a voltmeter attached to a good ground, touch the female connector that is attached to the yellow wire...you should read 5.0 volts........if you do, now take a jumper wire, attach it to the same good ground, and attach the other end to the yellow wire connector.....your coolant fans (both), should now run....
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Old 06-16-2016, 12:35 AM   #3
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If the above method does not force the fans on, or you want to take a different approach, you can also force the vehicle in to field service mode by shorting pins A and B together on the ALDL terminal, and then turning the ignition to run (but don't start the car). This should force the computer to command all fan relays on. If the fans do not run at this point, there is an electrical issue that will need to be tracked down, so you will need to trace the circuit. This mode should make it fairly easy, because the PCM should be powering the relays, so you should be able to see where you are losing power.

If the fans do come on in Field service mode, then they are likely working properly, and the computer is not commanding them on, which should be addressed by what Tech II has offered. I can't recall if the 5 volts seen is the max hot or max cold reading however, so I am assuming he is correct on that.
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Old 06-16-2016, 10:59 PM   #4
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Sorry, I forgot a step......if the fans run in the test I outlined, now take the jumper, and jumper the yellow to the black wire.....if the fans still run, then the problem is the sensor, or, you are not waiting long enough for the fans to come on (to reach the threshold temp), or you may have a discrepancy between the coolant sensor, and the gage sensor, i.e., the gage sensor may be showing a higher temp then what the coolant sensor is......I believe the gage sensor has a single green wire to it, on the opposite side of the engine....you would need a scan tool to observe both readings....

Now, if the fans run in the first step, but not the second, then you either have an open in the black wire circuit, or a bad ECM....

Naturally, if you don't have 5.0 volts in the first test, you have an open in the yellow wire, or a bad ECM....

If you have a good 5.0 volt circuit, and a good ground sensor circuit, and the fans don't run when jumpered, then it'* either a bad ECM or it'* the relay circuits....
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