I have a 2001 Pontiac Grand Am, 3.4L V-6. The cooling fans for the radiator will only come on when the A/C is turned on. Could it be a faulty relay? Does anyone have a wiring schematic they could share?

Well it is good that they do work when A/C is turned on! If I remember correctly, the fans wont normally kick on until the temp sensor reads around 225F.
Does your car over heat when stuck in traffic or at idle?

I think low speed is 221F, hi speed 235F....

As you can see from Soft Ride'* diagram, with lo speed, only the #1 relay is grounded, this put both fans in series, putting 6 volts on each fan...for hi speed, all three relays are grounded, changing the circuit from series to parallel and each fan gets 12 volts....

Thanks for the replies. I just bought the car and haven't had time to begin diagnosis yet. The previous owner said it ran fine around town but tended to run hot when under a load like climbing a long hill. He thought the radiator was partially plugged but again I haven't had a chance to check it out yet. I will update you once I get working on it, hopefully this weekend. He drove the car to my house (about two miles) and I took it for a drive, then let it idle while I looked it over and the temp gauge stayed steady at 220 degrees and both fans were running, with the a/c turned on.

Have you seen it run hot climbing a hill etc.?

Have you checked for obstructions in the condenser and radiator like filled with hay or bugs or birds or deer?

Here'* an update on my 2001 Grand Am GT 3.4L cooling fan inoperative except when A/C is on. I cannot get the fans to come on unless I turn on the A/C. then they run fine, even if I turn the A/C off. If I remove either the Fan #2 relay or fan mode relay, they shut down, then re-start when I plug the relay back in. Fan #1 relay makes no difference, they continue to both run. If I shut the car off and re-start it without the A/C on, the fans do not come on by themselves. I drove the car today about 15 miles, at speeds of 35 - 60 mph, made a few stops, etc and I cannot get the temp gauge to climb above 200 deg F. I verified the engine temp with my I/R heat detector, and right next to the temp sensor I got a reading of 206 deg F so I am thinking the engine was not hot enough to trigger the fans. It did not "boil over" and the water was not bubbling in the reservoir tank. Since it never goes above 200 deg F I am wondering if the previous owner removed the thermostat. I also tested the ECT sensor and it read 236-240 ohms at 200 deg F which is typical (normal) reading. I am going to check it in the morning with engine cold also.

I think my next step will be to take it out on the freeway and make a 50 - 60 mile run and see what happens. I am going on what the previous owner told me about the car, he said it overheated on long trips or in heavy traffic. He also told me he had replaced the intake manifold gaskets but I don't know how long ago or if the problem persisted after the repair. The car runs great, plenty of pep, will chirp the tires from a dead stop and does 0-60 in about 8-9 seconds (found that out today!)

I drove it today, up some hills and at speeds of 35-60 mph and I cannot get it to go over 200 deg F, I verified the gauge is accurate by measuring the temp right next to the ECT with my I/R heat detector. See my other post for other tests I have done, I am beginning to think the previous owner may have removed the thermostat. My next step will be to take it on the freeway for a 50-60 mile trip and see what happens.

Just idling the car should bring the temp up........once at normal operating temp, raise idle(in Park), to 2000 rpms.....temp should rise(if it doesn't, replace thermostat)........if you had no thermostat, the temp would get nowhere near 200F.....

Might be a good idea to replace the thermostat anyways. The PO might have removed it or put in a 180- or 160-degree unit or it might be a million years old . . . or it might be stuck just enough open that it lets it warm up and lets it flow enough coolant to keep it temperate under many activities, but not enough to allow more flow on long hill climbs.

As far as the radiator being plugged up, it doesn't happen too often these days but it is possible. How many miles are on it?