new to forums, electrical problem...

[aleroguy85]

Hi, i'm new to these forums and i have a 2001 alero 3.4. the worst car ever. my cooling fans not working. checked fuses, replaced relays, replaced temp sensor. The fans do not kick on when the engine is warmed up, and therefore the car overheats; the fans do not kick on when the a/c is turn on full blast. i've test the fan motors twice and both of them tested ok. i've been at this for weeks and haven't made any progress. any thoughts? thanks.

[geoffinbc]

Ok so in this diagram you have 3 relays and 3 fuses. If your fans test ok then its obvious you have a power supply problem. The fans run is series on low and parallel on high. This gives you 2 speeds. On your car the fans are not tuned on by the AC switch. The PCM knows you have the AC on and it Knows the operating temp and turns the fans on accordingly. So What I would do is check each relay for 12V. Then turn on the AC and you should at least have low speed which means the other side of the relay coil should be grounded. Your option is to manually ground the relay and see if the fan turns on. If not the relay is dead. Do it to all 3. Each relay should be hot at ALL TIMES. If not you have a blown fuse. Each fan motor should have a path to ground at all times. You will see that in low speed mode fan one and fan two are connected in series through the mode relay, and ground through a 30A ground fuse. In high speed mode fan one and fan two are each given a path to ground making a parallel circuit and fan 1 now grounds out through the mode relay directly to ground. Fan two is always connected right to ground through the ground fuse.

[aleroguy85]

Thanks for replying and supplying the information. I grounded both of the cooling fan relays manually and they turned on. I tried grounding the 3rd one (mode relay) and nothing happened. I bought a new relay today for the cooling fan mode and still no results. rechecked the fuses and none have blown. if the computer controls when the fans come on then maybe it's the computer and it needs to be replaced?

[geoffinbc]

Well that is a long shot. You made sure you checked the ground fuse right? If you cannot get the fans to turn on manually by grounding the relays then the problem is not with the computer. There has to be a bad fuse, bad relay or broken wire.

To get low speed to work you need to turn on Relay 1. For high speed you need to turn on all 3 relays.

[aleroguy85]

update: so i figured it out. I think my temperature gauge is a little off and/or giving wrong temp. information. Since I checked all the fuses and relays once more, I decided to let the car sit until it reached the 3/4 mark on the temp gauge and see if the fan kicks on. Sure enough, in between the 1/2 and 3/4 mark the fan kicks on. The fan never used to kick on at that temperature before i started working on it. It could possibly be other things making it start at that temperature but I'm pretty there might be something wrong with the temp sending unit. Also considering my rpm gauge topped out for a day or two then reset itself.

[geoffinbc]

Well don't always go by what the gauge says. They are more of an indicator than a measuring instrument. If you have a scan tool or if you can get your hands on one you can check what the ECM is seeing. The fans should turn on between 106*C and 109*C. You can also use a laser thermometer to see what the temp of the engine is. They will set you back less than $50

[aleroguy85]

i went and bought a laser thermo today and checked the temp of the engine as it was warming up and until the fans kicked on. They came on when they were suppose to at around 106c. Only other thing is the fans don't come on when my a/c is turned on. Although my a/c doesn't blow cold air anymore, I didn't think that had to do with the actual rad fans kickin on. or does it?

[IsaacHayes]

The A/C fans will only kick on if they need to. If it's cold temp outside it won't kick them on. Is your compressor clutch engaging? If not then you have leaked out enough refrigerant that the pressure switch see's that it's low and won't engage the clutch.

In summary, A/C has to work (clutch engage) and it has to be a certain pressure/and or temp before it fires up the rad fans.

[geoffinbc]

Agreed. This is not your typical old school system where the fan comes on every time the clutch on the pump engages. The PCM commands the fan on as it sees fit.

Good news to hear your fans are working as they should.

[aleroguy85]

ah ok. those damn computers and their parameters lol. im just glad the fans kicked on when suppose too. thanks for the help.