cooling fans / motors

Is anyone familiar with problems with the cooling fans? Mine seems to not want to turn on when the engine gets hot....but it will when i turn on the a/c. I checked relays and replaced my eng. temp. sensor by the intake.....when the sensor is removed, the fans automatically turn on to the high speed but when the sensor is in, it turns back off....

What is the temperature gauge reading? Normally, the fans do not turn on until the engine reaches over 220 degrees in normal driving conditions. The powertrain control control module (PCM) through output module drivers is what turns the fans on/off by controlling the cooling fan relays. It references to the engine coolant temperature sensor (ECT) to monitor engine temperature by sending a 5v reference signal to the ECT which is a thermal resistor that varies resistance and then sends the varying signal back to the PCM to determine whether fans should be turned on. If you disconnect the ECT the fans should go to the high position.

that sounds about right......my temp just keeps going up and up the most let it get to was 3/4 to the top before i turned on my a/c. I'm sure that it would go up even higher if i didn't. man, i really appreciated. If you have any more helpful comments, let me know. I will try to check on th pcm. Once again, thanks, nate.

I am having the same trouble with my 99 Alero fans work with A/C but not on their own.Did you ever fix your problem?Thanks

No, i sure didn't. I have been to lazy to try harder but I am still stumped on this problem. But I am planning on getting it scanned with a good scanner, that should pinpoint the problem.

Good morning - I hope this thread is still monitored. I just started trying to troubleshoot the same problem on my 1999 3.4L Alero (cooling fans do not come on unless the heater fan is on - engine overheats, but temperature gauge reads reasonable temperature.)

Has anyone had any luck with solving this problem?

bnaylor3400 had mentioned that disconnecting the ECT would cause the fans to go on - I was thinking, since resistance in the ECT goes down as temp goes up that bridging the wires on the ECT connector (zero resistance) would cause it to turn on. Please let me know what you think.

Also, I believe it was the same person (you are a godsend sir!) that mentioned that the ECT sends a signal to the PCM AND the temp gauge on the dash - does this imply that if the temp on the dash is reading expectedly, that the ECT is sending a 'good' signal to the PCM as well? (i.e. my problem is NOT the ECT?) I am running out to my car at lunch to try disconnecting it!

I have already checked all the fuses, relays, wiring connections, and everything is good. I am starting to sweat and shake in thoughts that this may be related to the PCM. Please god. . .someone tell me its not something to do with the PCM. PLEASE!! :)

Good morning - I hope this thread is still monitored. I just started trying to troubleshoot the same problem on my 1999 3.4L Alero (cooling fans do not come on unless the heater fan is on - engine overheats, but temperature gauge reads reasonable temperature.)

Has anyone had any luck with solving this problem?

bnaylor3400 had mentioned that disconnecting the ECT would cause the fans to go on - I was thinking, since resistance in the ECT goes down as temp goes up that bridging the wires on the ECT connector (zero resistance) would cause it to turn on. Please let me know what you think.

Also, I believe it was the same person (you are a godsend sir!) that mentioned that the ECT sends a signal to the PCM AND the temp gauge on the dash - does this imply that if the temp on the dash is reading expectedly, that the ECT is sending a 'good' signal to the PCM as well? (i.e. my problem is NOT the ECT?) I am running out to my car at lunch to try disconnecting it!

I have already checked all the fuses, relays, wiring connections, and everything is good. I am starting to sweat and shake in thoughts that this may be related to the PCM. Please god. . .someone tell me its not something to do with the PCM. PLEASE!! :)

We're still here. Whenever someone makes a new post all the ones that weighed-in get an email.

The PCM is a possibility if all else fails but before that there are a few things you can do. When you disconnect the electrical connector to the coolant temp sensor (ECT) and then fire up the engine within a matter of seconds both fans will turn on in high speed (you'll hear it). BTW - The temperature gauge does use the same sensor. And make sure the AC is off when you try this test. When the ECT connector is off the IP gauge will not work properly so it will be quite obvious that they share the ECT.

Now if you disconnect the ECT and nothing happens then that means the PCM may not be processing the signal from the ECT correctly. If the temperature gauge on the IP reads OK then the signal is outputting the ECT and getting to the PCM. It should be the yellow wire on the ECT electrical connector. The temperature gauge output is another pin on the PCM connectors to the IP gauge.

Another possibility is the PCM is working but the cooling fan relays are not working correctly but I doubt that because you can get the fans to come on when the AC is turned on to MAX and hi fan speed.

However, when the AC is off the PCM may not turn on the engine fans until it sees the engine temperature at around 220 degrees or so and higher. This is programmed into the PCM. Depending on where you live and as long as winter is over in your area sometimes going to a 180 degree thermostat helps. I recall someone had actually wired a switch to the cooling fan relays to turn on their fans.

Just for reference the ECT is located right under the thermostat housing on the intake manifold. The cooling fan relays are located in the engine compartment fuse box. The PCM is located under the driver's side of the dashboard to the left.

What signs do you have that the engine is overheating and what area of the IP gauge is the temperature reading?

THANKS!! I appreciate the quick reply. I will try this test tonight.

Fortunately for me, winter IS particularily long here *sigh* so even when sitting for a short while there is lots of cooling just in the air without the fans, and as long as the vehicle is moving, all is well. When it gets warmer outside, and when sitting for prolonged periods (more than a couple minutes) the temp gauge will creep above the half-way mark. Before I had this problem it would NEVER go any higher than half. The worst I have had it now is *nearing* the 3/4 mark. The engine is noticably hotter when this occurs. My short term fix was to crank the heater motor and hope the heater core pulled off some of the heat. Little did I know you could fire the fans full blast by cranking the AC! That would have been much nicer. . .

Strangely, I can get the cooling fans to come on (it seems at a low speed though) when the AC is off, but the heater fan is on (second or third speed setting, I didnt have enough time to test fully). I was just noticing this today, and it occurred to me that it is probably a safety feature. I will try with the AC on (holy cow - if I can remember where the button is!:grinyes: ) and see if the fans will come on high speed.

I tested all the relays by switching with others within the fuse panel (how convenient that they made some relays similar for different functions! They must not have been thinking about it!) Anyhow, they all seem to be functioning well.

I'm not crazy about having a hard-wired solution for turning on the fans, but if it *is* the PCM and it costs anywhere near as much as I expect. . .hmmmm.

I read another post you had placed re: the resistance across the ECT - I will try that as well and post again. Thanks again for all the help - it seems like quite a few Alero owners need it! ;)

THANKS!! I appreciate the quick reply. I will try this test tonight.

Fortunately for me, winter IS particularily long here *sigh* so even when sitting for a short while there is lots of cooling just in the air without the fans, and as long as the vehicle is moving, all is well. When it gets warmer outside, and when sitting for prolonged periods (more than a couple minutes) the temp gauge will creep above the half-way mark. Before I had this problem it would NEVER go any higher than half. The worst I have had it now is *nearing* the 3/4 mark. The engine is noticably hotter when this occurs. My short term fix was to crank the heater motor and hope the heater core pulled off some of the heat. Little did I know you could fire the fans full blast by cranking the AC! That would have been much nicer. . .

Strangely, I can get the cooling fans to come on (it seems at a low speed though) when the AC is off, but the heater fan is on (second or third speed setting, I didnt have enough time to test fully). I was just noticing this today, and it occurred to me that it is probably a safety feature. I will try with the AC on (holy cow - if I can remember where the button is!:grinyes: ) and see if the fans will come on high speed.

I tested all the relays by switching with others within the fuse panel (how convenient that they made some relays similar for different functions! They must not have been thinking about it!) Anyhow, they all seem to be functioning well.

I'm not crazy about having a hard-wired solution for turning on the fans, but if it *is* the PCM and it costs anywhere near as much as I expect. . .hmmmm.

I read another post you had placed re: the resistance across the ECT - I will try that as well and post again. Thanks again for all the help - it seems like quite a few Alero owners need it! ;)

Oh I see you're up North in Canada. The temp gauge on our '02 Alero GL2 (3.4L) never gets over the half mark and I'm in the desert Southwest U.S. I can see why your fans don't come on that often.

A PCM can be expensive new. Also a new one needs to be programmed or flashed by a GM dealer. But you can try a salvage yard but it must be the same for your year, model and engine size Alero. Also you can get a used PCM on EBay for $100 or less.

Another suggestion is to get another ECT sensor and try it. They do go bad or get out of calibration. So the resistance test may help. All you need is a digital multimeter. Maybe it is sending out the improper signal to the PCM but not enough to trigger the SES/CEL light. Plus they don't cost that much.

One other thing is to get the cooling system flushed. If you still have the original Dexcool coolant, it becomes worthless after about 5 years. You don't have to use Dexcool coolant. Companies like Prestone make Dexcool compatible anti-freeze. Prestone Exnded Life yellow container.

I think I have tried everything but obviosly not. When i take the ECT out, that is the only way I can get the fans to come on besides using the A/C. I have tried the relays too. Is there anything else anyone can think of? thanks all. Nate

Hey Nate - you can do what I eventually did. Sell it. Worked like a charm.

Here's what didn't work:
-New thermostat
-New ECT
-Cooling system flush
-Replacing relays
-Screaming loudly at vehicle

I stopped at the water pump. At that point I had just lost all hope in it, and for the life of me I can't see what the water pump has to do with the fan coming on. I am sorry to offend anyone, but life-after-Alero has been good to me. (now go find out how much the Alero has depreciated in its short life) :)

I think I have tried everything but obviosly not. When i take the ECT out, that is the only way I can get the fans to come on besides using the A/C. I have tried the relays too. Is there anything else anyone can think of? thanks all. Nate


Here is some info that may be helpful on cooling fan operation.

Cooling System Fans Description & Operation



The fan system includes the following components:

* Two (2) electric cooling fans (Left & Right)
* Three (3) fan relays (COOL FAN 1, COOL FAN & COOL FAN 2)
* Two (2) fuses (30 Amp Maxi fuses #6 [COOL FAN 1] & #1 [COOL FAN 2])
* All associated wiring & connectors

There are three basic modes for the fans: OFF, Low-Speed, and High-Speed. These modes are controlled by the Powertrain Control Module (PCM).

Fans OFF:

* When the coolant temperature is less than about 220°F (104°C) or
* The A/C refrigerant pressure is less than 190 psi (A/C off).

Low-Speed:

* When the coolant temperature is between about 220°F (104°C) and 230°F (110°C) or
* The A/C refrigerant pressure is more than 190 psi (1310 kPa) or
* When car is turned off and the coolant temp is more than about 284°F (140°C) and system voltage is more than 12 Volts. Fans will run for about 3 minutes.

High-Speed:

* When the coolant temperature is above about 230°F (110°C) or
* The A/C refrigerant pressure is more than 240 psi (1655 kPa) or
* When certain DTCs are set.

Other information:

* The thermostat for these cars normally opens at about 195°F (93°C)
* The "Engine Coolant Temperature" message should appear (on dash) if the engine coolant temperature is above about 262°F (128°C). PCM sends a message to the Instrument Panel indicating temperature.
* The "Engine Coolant Level" indicator should appear (on dash) if the coolant level goes below a certain level.

well, thanks everyone for you help. I will continue trying to get my cooling fans to work properly. If I succeed I will let you know. Nate.

I am sorry to offend anyone, but life-after-Alero has been good to me. (now go find out how much the Alero has depreciated in its short life) :)


LOL, once you drive off the lot your down $10k+ :rofl: And that's not a joke..

Well, looks like cooling fans are finally fixed! After trying everything, the last thing I tried was a PCM. I got one from Greenleaf Auto Recyclers for a little over $100. It was easy to replace. Its located right under the steering wheel. But when I swapped them and then tried to start my car, it would not start. So I looked up how to bypass the security on it......


If the car does not start after swapping PCM follow these steps

1. Turn key to "ON" position and leave for no less then 11 min.

2. Trun key to "OFF" position and leave for no less then 30 sec.

3. Try to start.

4. If it still does not work, repeat steps 1-3, up to four times.

My fans now work properly.

2001 Alero, 3.4 GL 97,000 Mi
I read through all the posts and there doesn't seem to be a same exact problem as what I'm having.
Last year while driving down the road I looked down and saw the temp gage dropped to cold. When this happend the rad. fans would run on high speed, with climate control fan off. A few days later the temp gage would read normal (half way mark) and no fans on. So I replace the coolent temp. sensor with a wells sensor. Had no problems until then.
Just last night was driving it and noticed the same thing, the temp gage was on the cold line, fans will startup on high right when the car is first started in the morning with the climate control off.
I was wondering if the coolent temp. sensor failed again or if there could be anything else. I still have a 1 yr. warr. on the sensor and could get another one. I don't know what the resistance is supposed to be on some temps though if I wanted to test it.
Any help would be appriciated
Thank You

2001 Alero, 3.4 GL 97,000 Mi
I read through all the posts and there doesn't seem to be a same exact problem as what I'm having.
Last year while driving down the road I looked down and saw the temp gage dropped to cold. When this happend the rad. fans would run on high speed, with climate control fan off. A few days later the temp gage would read normal (half way mark) and no fans on. So I replace the coolent temp. sensor with a wells sensor. Had no problems until then.
Just last night was driving it and noticed the same thing, the temp gage was on the cold line, fans will startup on high right when the car is first started in the morning with the climate control off.
I was wondering if the coolent temp. sensor failed again or if there could be anything else. I still have a 1 yr. warr. on the sensor and could get another one. I don't know what the resistance is supposed to be on some temps though if I wanted to test it.
Any help would be appriciated
Thank You

Sorry but please check the date and do not resurrect old threads. Best to start a new post. Thread closed.