Cooling Fans

[chilly13]

I need some help from the experts. My cooling fans won't turn on in the car and I've tried tracking down the problem. I'm kind of at a loss at this point. 2007 Pontiac G6 3.5l V6. Here is the wiring diagram for the cooling fans via Alldata. I've checked the fuses, used a power probe on the relays and they work, checked the fans with the power probe and they turn on, checked for any breaks in the wiring from the connector back to the relay's slots with the fluke, the relay and fuse slots have 12.6 volts going to them. I checked the ground from the right cooling fan. I also checked if the coolant temp sensor was working and verified it did with my little scan tool. I have not looked into the ECM or BCM wiring at this point. I am not a professional and certainly not good with electrical issues. Any help will be greatly appreciated. Do I need to chase wires from the fuse box if I have voltage to the correct relays and fuse locations? Any ideas will be greatly appreciated and ill start checking them off 1 by 1 if I have to. I don't want to wire a switch for the fans to turn on. I'd like to find the culprit. I have access to a fluke, power probe, and basic scan tool. Thanks everyone! If anyone has time to explain it, what do all the letters and numbers mean by the wiring in this all data picture. for example the yellow wire by the ECM says 410 Yellow 55 21 and under it says C3 and C2.

 

[75gmck25]

It appears that the cooling system sending unit sends a signal to the ECM, and then the ECM activates the high and/or low speed relay. It also looks like the sending unit is a simple resistive probe that works like most older cars, but it does not show any resistance values to use for testing.

Can you get access to the 335 Dark Green or 473 Dark Blue wires coming into that fuse block at the top? Or maybe you can pull one of the relays out and get access to the relay socket. What you are looking for is whether the ECM is sending a signal to those relays when the car heats up. If you never get voltage on either one of those wires, regardless of engine temps, then either the temp sensor is bad or the ECM has an issue.

AFAIK, all the numbers are just a wire numbering scheme to identify specific wires, and I think the C3 and C2 are probably terminal numbers in the connectors.

 

[Chuckster in NJ]

Try this: Disconnect the battery and wait 15 minutes then hook it back up.

 

[chilly13]

It appears that the cooling system sending unit sends a signal to the ECM, and then the ECM activates the high and/or low speed relay. It also looks like the sending unit is a simple resistive probe that works like most older cars, but it does not show any resistance values to use for testing.

Can you get access to the 335 Dark Green or 473 Dark Blue wires coming into that fuse block at the top? Or maybe you can pull one of the relays out and get access to the relay socket. What you are looking for is whether the ECM is sending a signal to those relays when the car heats up. If you never get voltage on either one of those wires, regardless of engine temps, then either the temp sensor is bad or the ECM has an issue.

AFAIK, all the numbers are just a wire numbering scheme to identify specific wires, and I think the C3 and C2 are probably terminal numbers in the connectors.

Thanks for the reply! I believe the sensor is fine because I watched it rise with the scan tool while the vehicle was on. As for the wires, i can pull the relay and access the tips, should I try to find the other end at the ECU? see for breakage?

 

[chilly13]

Try this: Disconnect the battery and wait 15 minutes then hook it back up.

the battery has been off, just did the head gasket and had to get a new battery

 

[wssix99]

My cooling fans won't turn on in the car and I've tried tracking down the problem. I'm kind of at a loss at this point. 2007 Pontiac G6 3.5l V6.

What is your problem? Are you overheating?

The fans are controlled by the ECM, which is smarter than us about this. It will command the fans on and off. ("Low" mode is one fan, only and "High" mode is both fans.) They should only come on when the cooling system overheats. If the system passively cools itself at a given speed or ambient conditions, the fans will stay off.

The Factory Service Manual will describe the conditions for the fans coming on and off in the troubleshooting section for cooling.


I have seen people having issues with overheating (on GM cars) due to pressure. If the system does not pressurize, then the coolant will boil at a lower temperature before the fans might otherwise come on. If this happens to you, I would start with a pressure test and also testing the radiator cap. (Particularly if the boil over is happening with temperatures in the low 200's)

 

[chilly13]

What is your problem? Are you overheating?

The fans are controlled by the ECM, which is smarter than us about this. It will command the fans on and off. ("Low" mode is one fan, only and "High" mode is both fans.) They should only come on when the cooling system overheats. If the system passively cools itself at a given speed or ambient conditions, the fans will stay off.

The Factory Service Manual will describe the conditions for the fans coming on and off in the troubleshooting section for cooling.


I have seen people having issues with overheating (on GM cars) due to pressure. If the system does not pressurize, then the coolant will boil at a lower temperature before the fans might otherwise come on. If this happens to you, I would start with a pressure test and also testing the radiator cap. (Particularly if the boil over is happening with temperatures in the low 200's)

Interesting, thanks for the reply. It isn’t over heating as far as I’m aware. It gets up to temp and stays there, as far as the gauge in the car says. Since I’ve noticed the fans, I don’t sit at full temp very long. I thought I could turn them on manually by using the blowers inside the vehicle eventually. The fans won’t turn on when the car is at full temp, they also won’t turn on when I try using the inside AC blowers. So you’re saying it’s possible that I haven’t met the conditions yet for them to turn on and they could be working fine. I believe my pressure is fine but I may try to do some of these tests just in case. I’ve always assumed Turing the fans on inside would eventually turn the cooling fans on. What’s your thoughts about that too? Thanks for the response!

 

[dscheidt]

I would bet there's an active test for the cooling fans accessible with a good scan tool. If the fans don't run, fix that. If they do, that establishes that the wiring is good, and the computer has control of them. Then, if they don't come on, you kow it's because the computer hasn't commanded them to. Troubleshoot that. . A newer car would probably have pids for all the inputs, but I doubt this one does, but it's either because the engine isn't warm enough, or it's getting wrong data. (but plausible wrong data. Most GM cars will default to max fan if the computer is missing data, or the data seems wrong.)

 

[Chuckster in NJ]

Just curious, are you the original owner? Did you just start having this problem? Why did you do the head gasket (over heating, high mileage, thermostat failure, etc)?
The reason I asked is because "IF" the car was pre owned the previous owner could have "toyed" with fan settings with a tuner or other reasons could have caused ECM issues.……. Maybe a "reflashing" of the ECM might help.

I am not familiar with your car but on my 2008 Challenger I was able to change fan temp settings with a Predator tuner. That hand held tuner did a lot of things to the ECM.

 

[chilly13]

I would bet there's an active test for the cooling fans accessible with a good scan tool. If the fans don't run, fix that. If they do, that establishes that the wiring is good, and the computer has control of them. Then, if they don't come on, you kow it's because the computer hasn't commanded them to. Troubleshoot that. . A newer car would probably have pids for all the inputs, but I doubt this one does, but it's either because the engine isn't warm enough, or it's getting wrong data. (but plausible wrong data. Most GM cars will default to max fan if the computer is missing data, or the data seems wrong.)

I bypassed all the wiring and got the fans on with a power probe. I seem to recall not getting voltage through to the connector. I have power to the fuse block and relay. I removed the relay and checked if they worked, they do in fact work, but when I reinstall I’m getting a low voltage at the wire connector that hooks up to the fans themselves. I could be measuring incorrectly but that seemed weird to me. The wires are not broken tho because I chased them back to the relay slot and got continuity

 

[chilly13]

Just curious, are you the original owner? Did you just start having this problem? Why did you do the head gasket (over heating, high mileage, thermostat failure, etc)?
The reason I asked is because "IF" the car was pre owned the previous owner could have "toyed" with fan settings with a tuner or other reasons could have caused ECM issues.……. Maybe a "reflashing" of the ECM might help.

I am not familiar with your car but on my 2008 Challenger I was able to change fan temp settings with a Predator tuner. That hand held tuner did a lot of things to the ECM.

I am the 3rd owner, first owner of if I recall was an older lady, 2nd owner was my sister and then myself. I don’t imagine anyone tuned it but that’s a very good point you make. I cannot verify if they worked in the past or not. I never had an over heating problem so I never checked. I only drive it to work and back which is just down the road. It never gets to temp honestly. I’ve had it 8 years and barely put any mileage on it. I’ve been chasing coolant leaks for a long time and finally an exhaust gasket failed and I thought I saw a drop of coolant come out of the flange. I was pulling into work when it happened so I just parked it. When I got it home, I pulled the plugs and 1 of the plugs was a little wet. I must say, very very slow coolant leak. Wrenching is just a hobby and I have 2 other vehicles so I got an engine gasket kit from mahle clevet and fel-pro on a wholesaler discount on rock auto and did the head gasket. I wouldn’t say it was a total failure but the gasket was certainly compromised. Anyways it’s all back together and all the new stuff I added along the way, water pump, oil pan gaskets, many coolant lines and o rings, injector seals…etc. I went for a test drive up the street and pulled over to check everything under the hood when it was at temp, the fans were not on. Confused, I drove it home and here we are

 

[Chuckster in NJ]

I am the 3rd owner, first owner of if I recall was an older lady, 2nd owner was my sister and then myself. I don’t imagine anyone tuned it but that’s a very good point you make. I cannot verify if they worked in the past or not. I never had an over heating problem so I never checked. I only drive it to work and back which is just down the road. It never gets to temp honestly. I’ve had it 8 years and barely put any mileage on it. I’ve been chasing coolant leaks for a long time and finally an exhaust gasket failed and I thought I saw a drop of coolant come out of the flange. I was pulling into work when it happened so I just parked it. When I got it home, I pulled the plugs and 1 of the plugs was a little wet. I must say, very very slow coolant leak. Wrenching is just a hobby and I have 2 other vehicles so I got an engine gasket kit from mahle clevet and fel-pro on a wholesaler discount on rock auto and did the head gasket. I wouldn’t say it was a total failure but the gasket was certainly compromised. Anyways it’s all back together and all the new stuff I added along the way, water pump, oil pan gaskets, many coolant lines and o rings, injector seals…etc. I went for a test drive up the street and pulled over to check everything under the hood when it was at temp, the fans were not on. Confused, I drove it home and here we are

Since you checked the obvious, I hate to be the "bringer of bad news" but I suggest taking it to someone with a comprehensive diagnostic scanner to see what is happening with the ECU. This will save you time and aggravation on testing things you can’t see.

 

[chilly13]

I believe you may be right. The relay slots are receiving the voltage, I’ve verified the relays work, but the connector to the fan isn’t getting full voltage. In fact it’s very very little. So I’m thinking u guys are right and the ECM isn’t sending its signal to turn it on. I’ll check for continuity I suppose to the ECM terminals but after that I think I’m SOL

 

[wssix99]

So you’re saying it’s possible that I haven’t met the conditions yet for them to turn on and they could be working fine.

I'm 99% certain this is the case. If you don't have a problem... then you probably don't have a problem.

This situation is common and people have come across it ever since GM went to computer control for the fans. (This saves power and improves fuel economy.)

To test the fans, you need a GM Tech2 scan tool or another higher-end scan tool with test functions. In the test menu, there should be commands to test the fans and the software will tickle the ECU to command the fans on (as it would during normal operation) and you should be able to observe the fans in "Low" and "High" mode that way.

I expect that with the cool weather right now, conditions are really nice and the fans aren't needed. If you come back on a 100 degree day, those things will be running, especially if you are at idle and no air is moving over the radiator.

 

[aka Larry]

The fans won’t turn on when the car is at full temp, they also won’t turn on when I try using the inside AC blowers.

I'm not a tech, but every car I own turns on both fans as soon as the A/C compressor kicks on.

 

[chilly13]

I'm 99% certain this is the case. If you don't have a problem... then you probably don't have a problem.

This situation is common and people have come across it ever since GM went to computer control for the fans. (This saves power and improves fuel economy.)

To test the fans, you need a GM Tech2 scan tool or another higher-end scan tool with test functions. In the test menu, there should be commands to test the fans and the software will tickle the ECU to command the fans on (as it would during normal operation) and you should be able to observe the fans in "Low" and "High" mode that way.

I expect that with the cool weather right now, conditions are really nice and the fans aren't needed. If you come back on a 100 degree day, those things will be running, especially if you are at idle and no air is moving over the radiator.

Wow, imagine this is the case. Could explain why the connector to the fan doesn’t have voltage but up to the relays is good. But shouldn’t I be able to bypass by manually turning on the blower fans inside the vehicle.

 

[chilly13]

I'm not a tech, but every car I own turns on both fans as soon as the A/C compressor kicks on.

My other vehicles as well.

 

[wssix99]

I'm not a tech, but every car I own turns on both fans as soon as the A/C compressor kicks on.

GM is different.

 

[Firebrick43]

Have you disconnected both the PCM and the relay and checked for resistance across both ends of the dk blue and dk green wires?

 

[chilly13]

GM is different.

This is a scenario I hadn’t considered

 

[wssix99]

Wow, imagine this is the case. Could explain why the connector to the fan doesn’t have voltage but up to the relays is good. But shouldn’t I be able to bypass by manually turning on the blower fans inside the vehicle.

The blower fan inside the vehicle is only for the cabin. The radiator fans only move air over the radiator to help it be more efficient.

Radiators move air over themselves passively via convection, but this is pretty weak. More air moves over them and they become more efficient when the car is moving forward. On really hot days, these passive types of air movements aren't enough and the fans make even more air move over the fins and we get more out of the radiator.

Old cars (including GM's cars in the '90s and older) would kick on the fans automatically under certain conditions. In the late '90s, GM started moving this control to the ECU for more efficiency. The LS Corvettes and descendent LS platforms all got this treatment and the G6 came along at the perfect time to inherit this stuff. (The diagram you posted functions the same as the LS cars of the era.)

 

[chilly13]

Have you disconnected both the PCM and the relay and checked for resistance across both ends of the dk blue and dk green wires?

I haven’t yet, last night I was looking into it. I think it’s pin 17 and 56 or 58. Going to do that today after work. Did u happen to mean ECM connector and chase it to the relay slots like in the image on AllData?

 

[Firebrick43]

I haven’t yet, last night I was looking into it. I think it’s pin 17 and 56 or 58. Going to do that today after work. Did u happen to mean ECM connector and chase it to the relay slots like in the image on AllData?

Yes, the ECM. Dont really need to chase it per sey. Just pull the relays and unlatch the connectors at the ecm and measure resistance between the relay pin and respective ecm pin. Yes to pins 17 and 58.

Also with the relays removed you should have 12v at the red arrows.

 

[dscheidt]

GM is different.

No, lots of fans are now entirely computer controlled. There's no good reason the fans need to run just because the AC is on, and plenty of reason not to run fans if they're not needed.

 

[kbeefy]

There is a good chance you just haven't gotten it hot enough to turn on the fans. When you monitor ECT with your scantool how hot is it getting? I've seen vehicles not turn on the fans until they were above 210.

A quick test I do is to Start the vehicle and turn on the AC. Not just the HVAC blower, but engage the AC so the clutch is spinning the compressor and the lines get hot/cold. That will put alot of extra heat into the cooling system without the car moving. Then watch the ECT and wait for the fans to engage.

It is also possible that you have an air pocket in the cooling system and the ECT probe is not reading correctly.

 

[walta]

No, lots of fans are now entirely computer controlled. There's no good reason the fans need to run just because the AC is on, and plenty of reason not to run fans if they're not needed.

The cooling must run whenever the AC compressor is running! The AC system requires air flow across the condenser coil in front of the radiator. This cools the high pressure gas so it can condenses into a high pressure liquid. In short with out the air flow from the fan the AC can’t cool the car.

OK, maybe the computer is smart enough to only run the fan when the car is stopped but I am pretty sure the OP is not testing the car while it is in motion.

Walta

 

[walta]

Yes, the ECM. Dont really need to chase it per sey. Just pull the relays and unlatch the connectors at the ecm and measure resistance between the relay pin and respective ecm pin. Yes to pins 17 and 58.

Also with the relays removed you should have 12v at the red arrows.

For me troubleshooting with an ohm meter is a last resort. Let’s get some voltage reading at the green and blue arrow in your diagram. For now, it does not matter what end of the wire you take the reading whatever end is easier to get at is fine. But get the reading when the car is warm enough the computer will have the fans turned on. 12V would indicate the computer want the fans off and less than 1V indicated the computer want the fan on.

Note turning on the AC should force the fans on.

Note when the low relay gets the 0 volt signal the 2 fans will be in serries and they should both run at half speed. If one of the fans is bad it will stop the other from running on low speed.

Walta

 

[dscheidt]

The cooling must run whenever the AC compressor is running! The AC system requires air flow across the condenser coil in front of the radiator. This cools the high pressure gas so it can condenses into a high pressure liquid. In short with out the air flow from the fan the AC can’t cool the car.

OK, maybe the computer is smart enough to only run the fan when the car is stopped but I am pretty sure the OP is not testing the car while it is in motion.

Walta

No, the condenser coil needs enough cooling to reject the heat removed from the car interior. That may require running the fans, it might not. Depends on ambient conditions, and speed. If it's 50f, and the climate is set to less than max, turning the AC on might not even engage the compressor, but even if it does, it may well be that there isn't enough heat to require the fan. In most situations, the fans don't need to run full out, because they're sized for whatever the worst expected condition is (probably stopped after a hard drive at high ambient temps), and you need less cooling most of the time. Running the fans only when it's required saves fuel and noise. There's no downside to doing it this way, because all of the sensors required exist for other purposes, it's just a little bit of software. (and the default strategy, in the absence of good inputs, is to run the fans at full speed the whole time the engine is running, which will both prevent the engine from overheating, and annoy the operator enough they take it in).

 

[chilly13]

Yes, the ECM. Dont really need to chase it per sey. Just pull the relays and unlatch the connectors at the ecm and measure resistance between the relay pin and respective ecm pin. Yes to pins 17 and 58.

Also with the relays removed you should have 12v at the red arrows.

Alright, just checked for continuity and we’re good at those connections. And yes, I do have voltage to those locations

 

[chilly13]

No, lots of fans are now entirely computer controlled. There's no good reason the fans need to run just because the AC is on, and plenty of reason not to run fans if they're not needed.

So you agree with Wssix99 and the cooling fans may not be turned on with my AC fans. I hadn’t ever heard of this until today. I have a 2015 Silverado and those cooling fans turn on with the AC fans on.

 

[chilly13]

There is a good chance you just haven't gotten it hot enough to turn on the fans. When you monitor ECT with your scantool how hot is it getting? I've seen vehicles not turn on the fans until they were above 210.

A quick test I do is to Start the vehicle and turn on the AC. Not just the HVAC blower, but engage the AC so the clutch is spinning the compressor and the lines get hot/cold. That will put alot of extra heat into the cooling system without the car moving. Then watch the ECT and wait for the fans to engage.

It is also possible that you have an air pocket in the cooling system and the ECT probe is not reading correctly.

This could make sense, let me work on getting some of this back together and hook it up.

 

[chilly13]

The cooling must run whenever the AC compressor is running! The AC system requires air flow across the condenser coil in front of the radiator. This cools the high pressure gas so it can condenses into a high pressure liquid. In short with out the air flow from the fan the AC can’t cool the car.

OK, maybe the computer is smart enough to only run the fan when the car is stopped but I am pretty sure the OP is not testing the car while it is in motion.

Walta

Yes I am testing in the driveway you are correct

 

[chilly13]

For me troubleshooting with an ohm meter is a last resort. Let’s get some voltage reading at the green and blue arrow in your diagram. For now, it does not matter what end of the wire you take the reading whatever end is easier to get at is fine. But get the reading when the car is warm enough the computer will have the fans turned on. 12V would indicate the computer want the fans off and less than 1V indicated the computer want the fan on.

Note turning on the AC should force the fans on.

Note when the low relay gets the 0 volt signal the 2 fans will be in serries and they should both run at half speed. If one of the fans is bad it will stop the other from running on low speed.

Walta

I guess I’m a bit confused. To check the voltage there I would have to pull the relays but don’t we need the relays in so they engage and we can get a reading. Forgive me because I am starting to get confused with all the wires here. Also, would starting the vehicle and letting it run without the ECM plugged in, cause some issues?

I think I may have answered my own question. I can pull the relays and see what the ECM is sending when it’s ready to correct?

 

[walta]

I say put every thing back the way it was then back probe the blue and the green arrows with the car hot running with the AC on full. with the black prob on a ground go into the back of a connector with a small pin and touch the red probe to the pin and note the voltage reading.

Walta

 

[chilly13]

Alright, with the risk of looking like a jacka**, here it goes. After I verified the continuity in the ECM wires going to the relays, I decided to double check the cooling fans were in fact turning on with the power probe. After it all checked out, I put everything back together and started her up with the scan tool on to watch the cooling fan command and the ECT. Here's the fun part, and you can speculate and make your own decisions with this information. Its puzzling, but I took a little bit of what everyone said on here. With the car starting to rise in temp, I turned the A/C on and blowers on high, watching the cooling fans and watching the scan tool simultaneously. Nothing was happening and I was starting to make my play on the relays and go to probe when I decided to wait until full temp. Right as the car hit 200 degrees, the fans kicked on and the command said it was at 55 percent. Both fans turned over, I couldn't believe it. I let them run for a while and turned the A/C blowers off. The command lowered down to around 30 percent or so. So now, I'm troubleshooting where I went wrong to spark all of this to begin with. This entire time I'm letting the car idle because not only for the fans, but I wanted to check for leaks anywhere in the head gasket job. Reading through all the replies, early on in the thread, Wssix spoke of the cooling system not being pressurized correctly as being a possible culprit. Looking back, when I initially found the fans were not turning on, I noticed I had a leak in the T fitting under the reservoir. I didn't think much of it at the time, just need a new fitting. The gauge on the car said we were at operating temp anyways, so I assumed the cooling fans were not working. So today, I believe in fact the cooling system was getting pressurized correctly since the T fitting repair and the car reached the correct temp for the ECM to command the fans. As for the A/C blowers not turning on the cooling fans, I believe in my car, 07 Pontiac G6 3.5l v6, they in fact do not have any action on the cooling fans BEFORE the car gets to temp. Once the car was at temp and the ECM was commanding the fans, however, I could manipulate the cooling fans speed/command with the A/C blowers inside the vehicle. Again, I'm up for speculation if anyone wants to chime in. With my truck, I can manipulate the cooling fans well before operating temp with the blowers inside. I apologize for my foolishness to take time out of all yalls day/night for responses, but I have learned a hell of a lot, and thank you guys for all the help! This forum keeps saving my **** over and over again. I hope that someone stumbles upon this in the future and possibly gets some info they may just need. Hell, could just be my G6, who knows! I'm taking it to work tomorrow, right down the road but I'm going to hook up the scan tool and try the A/C blowers again before operating temp to see if they do turn on the cooling fans. Just for my own peace of mind.

 

[no704]

Good luck with it! And remember the old saying “If it ant’t broke don’t fix it!”

 

[chilly13]

Good luck with it! And remember the old saying “If it ant’t broke don’t fix it!”

lol I feel dumb but am certainly grateful for all the help!

 

[no704]

And this is how we all learn. I can totally see your concern after all of that work and $$ into it.

 

[chilly13]

And this is how we all learn. I can totally see your concern after all of that work and $$ into it.

She’s running great now. Still have a small oil leak, the only thing I didn’t touch is the rear main. Not sure I can accomplish this on jackstands in the driveway though. Regardless, have some other projects I’ve been waiting to tinker with.

 

[Chuckster in NJ]

A few guys I know have used this on rear main seals with good results.…… May be worth a try for $16

BTW! Glad you got the fan issue figured out!