2002 Impala no low speed cooling fans

I have a 2002 impala 3800 that I've had to the dealer and they can't figure out what is wrong with my cooling fans. Sometimes everything works perfectly and others I only have high speed at 230* They replaced the ecm and nothing the same thing. Seems that if they work I can shut the car off and next time might not work. So , AC works perfect if fans are on when fans don't work AC quits unless I'm driving. I found conflicting info on the BCM. Some say it has nothing to do with fans and others that claim BCM could cause this intermittent fan failure.
When working properly, the low speed fans are on when ac is on, if AC is off they come on at 215* off at 210* only time high speed works is on at 230* and off at 225* when low speed fail to operate.

What is causing my issue? What do you suggest? First repair was $450 with no results.

What did you get for $450?

A ECM that didn't change anything.

Well, obviously, the problem was not happening while in the shop.......and it looks like, this was their best "guess"....

and they should have informed you of this......that it wasn't happening now.....that they "think" it is the ECM/PCM.......and then the ball is in your court, as to whether that part is installed....

With a Tech II scanner, a tech can command the hi and lo speed fans on, to check those circuits........

I do not see where the BCM comes into play here, but I do not have a manual to look at what the BCM controls....

For A/C operation, the control head sends an A/C "request" signal to the PCM.....the PCM checks the reading of the A/C pressure sensor....if ok, it then grounds the compressor relay and also the relay for low speed control.....if the fans do not come on, especially when the car is not moving, then pressure in the A/C system will be increased in the system, noted by the pressure sensor, and then when the PCM "sees" this, it will disable the clutch relay.....then as you drive down the road, air flows across the condenser, removing heat, and lowering pressure to a point where the PCM "sees" this, and then grounds the clutch relay again....

PCM also "reads" data from the coolant sensor, and based on this input, grounds the appropriate relays(there are 3 of them in this configuration)......only one is grounded for low speed(in this case the fans are in series, and only get 6 volts each)....for hi speed all three are grounded, and this causes them to be in parallel, with each getting 12 volts instead of 6 volts........

the fan circuits are common to both both systems, cooling and A/C......a bad connection, and arced contact in a relay, or an intermittent ground(corroded connection or wire broken inside the insulation, can kill the circuit operation).......

So the tech could have commanded hi and low speed operation for the cooling fans(with the Tech II), turned on the A/C and it worked, and concluded it was the PCM.......

The first thing I would have done, was check the ground for the circuit....there is only one.......then I would try to create the problem while moving harnesses as the fans ran.....then I would have suggested replacing all three relays, BEFORE condemning a PCM, especially if there were no codes at all(14 years of opening/closing, the contacts in those relays could be bad)......and as I said, it could even be a wiring issue.....with the fans running, the harnesses should be grabbed and moved while the fans are running, to try and create the problem........the other possibility is a bad fan, especially when they are in low speed mode, because they are then in "series"......

This is one of the problems techs run into, when a car is brought in, for an intermittent problem......if it's not happening, and he can't recreate it, all he can do is check for a possible TSB(bulletin) that might apply to your problem, or if he has seen a number of vehicles come in with your SAME problem, he can "recommend" a fix.....

But a tech, and it's shop should not tell a customer, they know what it is, if it's a guess on their part...in some cases, they may be right.....but they should inform you that, this is their best "guess", and leave it up to you to make the decision, on whether you want to "pay" for their best guess.........

From my memory, W-cars (as is yours) wait until a/c pressure hits 175psi to turn on low speed fan(s). So just having a/c on is not a test for low speed fan operation- it has to be in hot ambient as well.

Again, the Tech II is the best tool to test with- it will show a/c pressure and fan status- and you can command all fan speeds as well.

Most all other GM cars - the fans come on with a/c request, just not W-cars.

I showed the tech it wasn't working with a scan tool of mine that shows temps. It was 228* and no fans working. He obviously can see they are not on but insists with my "rinky dinky little aftermarket tool" there isn't any way he can tell if it's calibrated correctly. Since the first week of May when I had the repair made I've only confirmed 3 times the fans were on correctly all other times it doesn't work so I find it hard to believe they were always working when they checked them. They had it a week each time I had it in there. I told them no low speed fans, high always work. He diagnoses no high speed tech ll wouldn't command high speed on so "found bad internal ground" replaced ECM high speed now working.
Before I took it to them I cleaned the ground up front and swapped relays it was still the same no low speed.

Well, obviously, the problem was not happening while in the shop.......and it looks like, this was their best "guess"....

and they should have informed you of this......that it wasn't happening now.....that they "think" it is the ECM/PCM.......and then the ball is in your court, as to whether that part is installed....

With a Tech II scanner, a tech can command the hi and lo speed fans on, to check those circuits........

I do not see where the BCM comes into play here, but I do not have a manual to look at what the BCM controls....

For A/C operation, the control head sends an A/C "request" signal to the PCM.....the PCM checks the reading of the A/C pressure sensor....if ok, it then grounds the compressor relay and also the relay for low speed control.....if the fans do not come on, especially when the car is not moving, then pressure in the A/C system will be increased in the system, noted by the pressure sensor, and then when the PCM "sees" this, it will disable the clutch relay.....then as you drive down the road, air flows across the condenser, removing heat, and lowering pressure to a point where the PCM "sees" this, and then grounds the clutch relay again....

PCM also "reads" data from the coolant sensor, and based on this input, grounds the appropriate relays(there are 3 of them in this configuration)......only one is grounded for low speed(in this case the fans are in series, and only get 6 volts each)....for hi speed all three are grounded, and this causes them to be in parallel, with each getting 12 volts instead of 6 volts........

the fan circuits are common to both both systems, cooling and A/C......a bad connection, and arced contact in a relay, or an intermittent ground(corroded connection or wire broken inside the insulation, can kill the circuit operation).......

So the tech could have commanded hi and low speed operation for the cooling fans(with the Tech II), turned on the A/C and it worked, and concluded it was the PCM.......

The first thing I would have done, was check the ground for the circuit....there is only one.......then I would try to create the problem while moving harnesses as the fans ran.....then I would have suggested replacing all three relays, BEFORE condemning a PCM, especially if there were no codes at all(14 years of opening/closing, the contacts in those relays could be bad)......and as I said, it could even be a wiring issue.....with the fans running, the harnesses should be grabbed and moved while the fans are running, to try and create the problem........the other possibility is a bad fan, especially when they are in low speed mode, because they are then in "series"......

This is one of the problems techs run into, when a car is brought in, for an intermittent problem......if it's not happening, and he can't recreate it, all he can do is check for a possible TSB(bulletin) that might apply to your problem, or if he has seen a number of vehicles come in with your SAME problem, he can "recommend" a fix.....

But a tech, and it's shop should not tell a customer, they know what it is, if it's a guess on their part...in some cases, they may be right.....but they should inform you that, this is their best "guess", and leave it up to you to make the decision, on whether you want to "pay" for their best guess.........

I agree I will not always be able to command them on with AC switch but regardless if I removed the AC system from the vehicle the low speed fans should still work off the CTS when it reaches 217* they only come on high speed at 230* faithfully and cool to 225* at this point the fans stop spinning until 230* again. At any point I can provide a ground at the relay and low will work.
I mention AC because when driving that's the first indication the low isn't working it high pressures and shuts down and won't work again until I can get air through it.
I realize the temp gauge isn't exactly accurate but you can obviously see when it's near 230* because it's 3/4 to the top at 200* it's just below half up to just over half. Usually runs around 218-220 on a hot day driving down the road with low speed NOT working when the low speed WORK ( vary rare but I caught it on video to prove at times they do work) it runs around 196-200 while driving with AC on. If it's cool at night I've seen it as low at 183* I have a 180* thermostat in it that came with the new lower intake gasket upgraded replacement kit.
From my memory, W-cars (as is yours) wait until a/c pressure hits 175psi to turn on low speed fan(s). So just having a/c on is not a test for low speed fan operation- it has to be in hot ambient as well.

Again, the Tech II is the best tool to test with- it will show a/c pressure and fan status- and you can command all fan speeds as well.

Most all other GM cars - the fans come on with a/c request, just not W-cars.

If the fans run like clockwork, on hi speed, then G101 is good(ground).....

Remember, in hi speed the fans are in parallel, in lo, they are in series....

I would be suspicious of coolant fan relay #2 ....1 and 3 are basically the same relay, with a single contact(relay has 4 terminals).....but #2 relay is different(relay has 5 terminals)....it has a double contact, meaning it switches circuits....if one contact is bad(for low speed), and the other is good( for hi speed), then you will not get lo speed....

Since you have hi speed, the ECM is commanding all three relays on.....on low speed only the #1 relay is commanded on, and we know that is good because you have hi speed......the other two relays are off, but like I said, #2 relay has two positions......and when off, the contact moves back to the low speed position.....if the contact is bad, you either have an open or a huge voltage drop at the contact, which will prevent enough voltage from running the two fans in series....you can verify the ECM is turning the low speed fans on, by disconnecting right cooling fan....this will be the one with the grey and white wires in the harness(the left coolant fan has light blue and black wires to it)....when temp reaches 220F, the low cooling fans should be on....disconnect the harness to the right fan, and with a test light to ground, probe the connector to the grey wire.....if it lights, you know the ECM is grounding #1 relay, and the problem is between the right fan and the left fan....could be a bad wire, or the #2 relay.....

Finally got it figured out! After nearly 3 months of fighting with the Chevy dealer, after about eight times of 50 mile round trips to pick up my broken car that was "fixed" the service manager finally agreed to check the car over with me present. I showed him the low speed fans did NOT work and high speed is all that would work. He confirmed for the first time that the PCM was not the problem and that he was sorry for being a "dick" to me. I showed him a service bulletin that said BCM was at fault for intermittent fan failure. They kept the car one more week replaced the BCM and fans are now fully functional and operate as they should. Best part is he saw us pull up and brought the keys out to me and again apologized for being an "ass hole" ( my wife and children were present) and that he backs his mechanics and they have never seen a BCM cause these issues. The bill for the BCM....NO CHARGE! he shook my hand and said he hoped that I'd still consider them in the future for repair work. If I can figure out how to attach the information on the BCM bulletin I will add them to this post.

Here is what I found and showed them to finally get it fixed.


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Finally got it figured out! After nearly 3 months of fighting with the Chevy dealer, after about eight times of 50 mile round trips to pick up my broken car that was "fixed" the service manager finally agreed to check the car over with me present. I showed him the low speed fans did NOT work and high speed is all that would work. He confirmed for the first time that the PCM was not the problem and that he was sorry for being a "dick" to me. I showed him a service bulletin that said BCM was at fault for intermittent fan failure. They kept the car one more week replaced the BCM and fans are now fully functional and operate as they should. Best part is he saw us pull up and brought the keys out to me and again apologized for being an "ass hole" ( my wife and children were present) and that he backs his mechanics and they have never seen a BCM cause these issues. The bill for the BCM....NO CHARGE! he shook my hand and said he hoped that I'd still consider them in the future for repair work. If I can figure out how to attach the information on the BCM bulletin I will add them to this post.

I'm kind of surprised and disappointed at the dealer for not finding this info to begin with. A quick bulletin search with your vehicles info, searching cooling fan, and the TSB pops right up. Should have been caught the first time in. Weird how you say that with low speed fans not running that the a/c didn't cool until there was sufficient air flow over the condenser. Some people don't think that cooling fans affect a/c operation. ;)

Agree, GMTech1.....when you can't fix your own cars by doing a simple search, that shop has problems...

Just checking back to give an update. Cooling fans still performing perfectly and the A/C is working excellent all the time. Thanks for the comments and hopefully this will help someone else.