Andy1

I've got my radiator fans controlled by the PCM with the three relay Fbody scheme. Been working fine for some months, but suddenly stopped working. I have a manual over ride where I can turn on either low or high speeds with a dash mounted toggle switch. The manual control works fine, which leads me to believe the fuses and relays are all ok. I have a separate sender for my temp gauge, so I can see what's going on. So I'm thinking my GM temp sensor has gone bad, or I've got a poor connection or broken wire. Any thoughts or recommendations on how best to chase down the root of the problem?

Thanks,

Andy1

gofastwclass

iTrader: (2)

If the temp sensor wiring is broken or shorted it will run super rich. I think the PCM will say the temp is -38 degrees or something impossible to attain.

I would use something like HP Tuners or EFI Live to scan the vehicle and actuate the fans independently of temperature. You can also verify the programming within those applications, but the calibration can't change on it's own.

Even a hand held scanner will give you a coolant temperature reading, even if it can't do bi-directional communication.

Andy1

I don't have HP Tuners, but is there a way to test the coolant temp sensor? Resistance measured at certain temps for example?

Andy1

Fivetears

I'd disconnect your PCM Connectors and check for continuity (ohms resistance) between Blue connector Pin 42 and your respective Low Fan relay ground wire, and check for continuity (ohms resistance) between Green connector Pin 33 and your respective High Fan relay ground wire. A sender failure would cause other problems too.