Radiator cooling fan will not run

[Deeson]

Here's a good one... My 99 Alero's radiator cooling fan is not operating when the temp rises above normal. I replaced the temperature sensor and let it warm up and no action. I took a 12volt light tester and stabbed it into one of the wires from the sensor and the fan started running, basically added a ground into the system. It ran for a minute and shut off. Did this twice to confirm. Any ideas?

[BNaylor]

Welcome to AF.

Is this with A/C on or off?

[Deeson]

Originally Posted by BNaylor

Welcome to AF.

Is this with A/C on or off?

Update... With the AC switch on or off, I cannot get the fans to come on. After the car had warmed up, I disconnected the sensor and the fans started running. However, my in-dash temp gauge stopped working. I may need to breakdown and buy a manual to trace the wires.

[BNaylor]

The IP temp gauge works off the the same engine coolant temp sensor (ECT) so that is normal and disconnecting the ECT puts it in failsafe mode mode meaning both cooling fans will turn on after a short delay. You may have a PCM module issue since it controls the cooling fan relays and fans.

The fans turn on in low speed mode when the engine coolant temp reaches around 220 degrees and hi-speed around 230 degrees but with A/C on you should see the fans turn on more frequently regardless of the above.