Has anybody had a problem with there cooling fan not turning on. All the wires are good because if you disconnect the ECT sensor the fan turns on and stays on all the time as a default mode. I just replaced my ECT sensor and it still isn't turning on. The only thing left in the PCM. I was just wondering if anybody has any input or confirmation to this message.

Got air conditioning? What about if you turn that switch on? (Should kick the fan on as well)

It doesn't come on very often on my car. Is your car actually overheating?

I don't know that mine comes on either come to think of it... whenever I am stuck in traffic for a while, my engine heats past the middle on the temp... once I start driving and get some air flowing it goes back down. Seems like my car shifts differently (automatic) when it is hotter too... almost like it's slower to respond. When does you car overheat (sitting in traffic, or while driving)?

No, I don't have A/C anymore. The needle on the gauge starts to go over the halfway point only while I sit in traffic. I just turn on the blower motor to cool if off. The fan is suppose to come if your going under 37mph and it's already at operating temperature.

TravCavZ24 wrote: Seems like my car shifts differently (automatic) when it is hotter too... almost like it's slower to respond. When does you car overheat (sitting in traffic, or while driving)?

thats because you have an auto tanny cooler built in the radiator. When the coolant gets hot in starts heating up the tranny fluid, this causes the tranny to shift funny.

My fan also turns on VERY late, I am going to be getting a larger aftermarket fan with a t-stat that makes it come on sooner.

Chris Pasco wrote:No, I don't have A/C anymore. The needle on the gauge starts to go over the halfway point only while I sit in traffic. I just turn on the blower motor to cool if off. The fan is suppose to come if your going under 37mph and it's already at operating temperature.

Uhh, since when? Mine never comes on, unless I turn on the A/C.. I never sit in traffic for more than just one light tho

my fan doesn't kick on until almost 3/4's of the way up, and that only happens in really bad traffic.


Desert Tuners

“When you come across a big kettle of crazy, it’s best not to stir it.”

I have a manual trans. The Fan use to operate normally. I already know it's the PCM but I was just curious if anyone else out there has had the same problem.

Chris Pasco wrote:I have a manual trans. The Fan use to operate normally. I already know it's the PCM but I was just curious if anyone else out there has had the same problem.

You are not the first person to have this problem. How do you know it is your ECU? The fan does not come on under 37 mph. Only if your AC is on, your car is at a certain temp (like 221F), and some CEL's will turn it on.

What are CEL's? The Fan is programmed by the PCM to turn on at certain times. 37 mph is the cutoff speed for when the Fan turns off. Haven't you noticed your fan sometimes comes on after you turn your car off. It stays on a little after to cool it down. Haven't you seen that sticker that stays "Warning: Fan may turn on at anytime". Also I do know it's the PCM because, if I disconnect the ECT sensor the "MIL" light comes on and automatically turns the fan on ALL the time. So that verifies that all the wires in the circuit are good. Second, I replaced the ECT sensor cause I thought that maybe it was out of calibration but it wasn't. The only other suspect is the PCM. And we don't have a ECU in our car. Chevy likes to refer to it as a PCM. Feel free to correct me. I do this for a living. Valenti Motors-Audi Technician. Watertown, CT

Chris Pasco wrote:What are CEL's? The Fan is programmed by the PCM to turn on at certain times. 37 mph is the cutoff speed for when the Fan turns off. Haven't you noticed your fan sometimes comes on after you turn your car off. It stays on a little after to cool it down. Haven't you seen that sticker that stays "Warning: Fan may turn on at anytime". Also I do know it's the PCM because, if I disconnect the ECT sensor the "MIL" light comes on and automatically turns the fan on ALL the time. So that verifies that all the wires in the circuit are good. Second, I replaced the ECT sensor cause I thought that maybe it was out of calibration but it wasn't. The only other suspect is the PCM. And we don't have a ECU in our car. Chevy likes to refer to it as a PCM. Feel free to correct me. I do this for a living. Valenti Motors-Audi Technician. Watertown, CT

Ok. No the fan does not come on at a certain speed. Also what year is your car? Yes when you disconnect a sensor the fan will come on because the CEL/MIL is on. CEL is check Engine Light. The computer does run the fan you are correct. If you have a ecotec car the fan might run when you turn the car off to cool it down (it is programed to do that), but has nothing ot do with the speed of the car. This also does not prove it is the ECU. Also the hole ECU/PCM crap give me a break we all know what I mean.

PCM, ECU, ECM, Computer, whatever..

It doesn't turn the fan on below 37mph. If it does, there's something wrong with your car.

I have GM service manuals. It doesn't mention 37mph for anything (I've read them enough times).

Oh, and if you're really a tech for a living... and you don't know what a CHECK ENGINE LIGHT (CEL) is... remind me never to bring my car to your shop

"Only if your AC is on, your car is at a certain temp (like 221F), and some CEL's will turn it on."

Some CEL"s. (Some Check Engine Lights.) I would have understood it better if you referred to them as DTC's. Diagnostic Trouble Codes.


First off, If your going to refer to certain aspects of the car's electronic systems, why don't you do it correctly. Second off, MIL is more of a common term. "CEL" is hardly used. But thanks for reminding me. Third, I didn't mean the Fan will come on under 37mph all the time. I'm just saying it will kick off automatically over 37mph.

My car is a 1997 Cavalier Z24. What is this certain speeds that you are talking about? I never said it would come on at "certain speeds". I said certain "times". There's different variables. But if you don't think it's the PCM, then what do you think it is?

Look, I am not trying to be a smart ass and step on anyone's toes. Seriously. I am just a specific person. I really appreciate your responses.

If you are so worried about when your Fan turns on, why not make yourself the switch an put in on or off when ever you damn will please.

my fan doesnt come on till after the half way mark if im sitting in traffic, never overheats tho..


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ayo 8 Iz Enuff

Ok, I don't know where you are getting these numbers and misinformaton, and frankly I don't care. I only come back now to this thread, to correct the mis-information.

Here's what the GM service manual has to say about it:

Quote:

Cooling Fan Operation

The Electronic Control Module (ECM) regulates the voltage to the cooling fan relay. The relay operates the fan when the engine coolant temperature exceeds 106 degrees Celcius or 223 degrees Fareinheit. The cooling fan will turn on automatically during extended idle conditions under 5 miles per hour. For diagnosis and location of the relay, refer to Electrical Diagnosis.

Okay? No 37mph cut off. No 221 F.

End of story.

...j

The infomation I got was from a MODUS scan tool.
When does your fan turn on?
Does it turn on when you use the A/C?
Does it turn on after you've been idling a awhile?
What temp on the gauge does your needle read when it does turn on?
Does it ever go past the half way point?

When does your fan turn on? Once in a blue moon from getting too hot. I live in cool climate Vancouver BC
Does it turn on when you use the A/C? Yes
Does it turn on after you've been idling a awhile? Only if I've been sitting in traffic for a long time
What temp on the gauge does your needle read when it does turn on?A bit above the middle point
Does it ever go past the half way point?It usually sits at the middle point, a bit higher if sitting in traffic

I've only ever once had the fan come on after I parked it.. but there are certain conditions for that as well.

Chris Pasco wrote:"Only if your AC is on, your car is at a certain temp (like 221F), and some CEL's will turn it on."

Some CEL"s. (Some Check Engine Lights.) I would have understood it better if you referred to them as DTC's. Diagnostic Trouble Codes.


First off, If your going to refer to certain aspects of the car's electronic systems, why don't you do it correctly. Second off, MIL is more of a common term. "CEL" is hardly used. But thanks for reminding me. Third, I didn't mean the Fan will come on under 37mph all the time. I'm just saying it will kick off automatically over 37mph.

My car is a 1997 Cavalier Z24. What is this certain speeds that you are talking about? I never said it would come on at "certain speeds". I said certain "times". There's different variables. But if you don't think it's the PCM, then what do you think it is?

Look, I am not trying to be a smart ass and step on anyone's toes. Seriously. I am just a specific person. I really appreciate your responses.

CEL is used on this site everyday CEL (check Engine Light), if you want to do it coirrectly so you say then it would be MIL (that is how the scantools read it). No reason to be a jerk.

Quote:

Okay? No 37mph cut off. No 221 F.

John thanks for correcting that info, I could not remember the exact temp it comes on.