Cooling fans won't turn on...

[Theautoguy]

1994 Pontiac Grand Prix w/3100.

Both cooling fans will not turn on. I can say the relays, fuses, harness and temp switch are good.

I can mechanically engage the relays and each cooresponding fan turns on so I know the harness and fans are good. I've replaced the temp switch. The fuses check out good. I also swapped in a different PCM with no change.

I believe the PCM controls the grounding for the fan circuit so I don't think there is any ground to look for. Is there anything I'm missing here?

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[LSx S10]

Does the fan turn on when you turn on ac?? If you feel like throwing parts at it, there are two sensors. One is a one wire connector on the back of the engine, drivers side of the rear head, and that is the temperature switch for the dummy light. The other is up by the thermostat and is a two wire, that one is the ecm ect. If you have a scan tool that will work for that car, see what the ect is reading. Might find your problem right there. But if i were you i would just throw a sensor at it and try again. 11 bucks from autozone

EDIT: sorry missed the part about the temp switch being good

 

[Carls2001ws6]

I'd say check the relay coil wires. Are they getting a voltage to the magnet side to pull the contacts? Is it getting enough voltage (12VDC) to pull the contacts? If your getting a good strong voltage than I would replace the relays. Electrically you relay could be good, but mechanically the electromagnet coil could be shorted out and not physically pulling the contacts.

Where do those wires go to? To the PCM? You replaced the PCM and the same thing happens?

At the very least wire the fans directly to your ignition switch. This way they always have voltage as soon as you start the car. They always run but it could buy you some time. It's so damn hot right now that overheating could happen very easily.