radiator fan wont turn on...

[BlackMage]

Admins feel free to move this, i wasnt sure where to put it. I am working on a 99 grand prix se with the 3100 series motor. The radiator fan wont turn on when it normally does and the engine begins to get hot. I checked all the relays, they are all workin as they should b, all fuses are good, power to and from the relays and fuses. The fans work, i ran jumper wires to them and they spin up. The coolant temp sensor is reading within spec, and there is also power at the connector to the fans. If I stick a pin into the connector(there are 4 wires, and one is hot) on one that is not hot, i can get the fans to turn on, but not at full strength. Any ideas as to what to check next? im at a loss here, im thinking faulty ground wire but i dont read any voltage on the ground side...does the computer control when to turn the fans on thru the ground?? maybe a bad ecu? thanks guys! -Will

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[jpacetti]

Maybe a bad coolant temp switch. Try removing the connector and see if the fan comes on. If it does then replace the switch. Otherwise the ecu controls the fan usually through the ccrm see if your getting power to there.