What actually triggers the radiator fans? Need some diagnostic help

[manhertm]

So after sitting for years, I'm slowly got my car up and running again. I originally parked it because of an overheating issue, which I later found was related to a cracked water pump impeller. I did a timing belt service and found some broken blades on my radiator fan. I bought a used fan set with shroud and spliced them to the FCM. So now the car is running, but I take it around the neighborhood to see if everything is working properly and it still overheats. I figured it was air in the coolant system, but I noticed the fans weren't turning on at all even with the car overheating. So I figured maybe I got some bad fans or a bad FCM. I bought another used fan set with FCM intact, so no splicing. Hooked it up, check the fan relay in the ECU box to make sure it was good(it looked perfect, no water issues in there) and went for another spin. The fans still aren't coming on. I read that for the AC to work, the auxiliary fan must come on. I cranked the A/C to the coldest and turned the vent fan all the way up and the fans still aren't moving. What else can I double check here. I'm ready to take it to a shop, but I feel like it'll be some minor issue I'm overlooking. Any suggestions?

[old guy]

Normally the fans are controlled by the fan control module based on a signal from the CTS in the lower radiator hose. However, if the fans are not coming on when the A/C is activated that would indicate a problem with the fan control module.

[manhertm]

I did get a
"16502 - Engine Coolant Temp. Sensor (G62): Signal too High
P0118 - 002 - Lower Limit Exceeded"

I've got a new lower sensor on the way, but I supposed I should just get a brand new FCM and eliminate the chance of it being bad. Is there any way to check the FCM for being faulty?

[gedrosselt]

You could check for a voltage to the fans with a multimeter when the fans should be on, or you could put 12v direct to the fans and see if they spin. In my case, the large fan shorted and blew out the FCM, so I have to replace both. Hopefully I can find a way to replace the fan w/o removing the radiator.

[eljay]

Normally the fans are controlled by the fan control module based on a signal from the CTS in the lower radiator hose. However, if the fans are not coming on when the A/C is activated that would indicate a problem with the fan control module.

I am bumping this thread instead of creating another with the same question as the title of this one... although my question/issue is just the opposite to the OP: my fans come on full speed right away.
While doing my coolant refill after a flush, I noticed that the moment I started the car (with engine completely cold), the radiator fans come on full speed immediately. Now, I had the heat on "HI" as I did a few warm up/drain cycles. So, is this the expected behaviour if I have the heat on high? Or should the fans be off at startup and only come on once the engine has warmed up fully to keep the coolant temp in check?
Torque app does not show any codes related to the cooling system, so should I assume the lower CTS is fine?

Edit: the temp gauge seems to behave fine and even with just idling goes up to the middle within 5 mins or so and stays there steady.

[old guy]

The fans come on high at start up when you have a DTC for a cooling system malfunction. That will not stop until you fix the issue and reset the DTC's. Use your TorquePro to reset all codes. Even if it isn't showing one. I suspect that will clear it.

[eljay]

The fans come on high at start up when you have a DTC for a cooling system malfunction. That will not stop until you fix the issue and reset the DTC's. Use your TorquePro to reset all codes. Even if it isn't showing one. I suspect that will clear it.

Thank you. The only codes I'm getting are misfire on #2 (P0302) and #1 (P0301) and random misfire (P0300). I have reset them during my first coolant flush and they came back just from idling the car, but the fans came on as well. Should I replace the lower CTS? Is it possible that the CTS connector got moisture inside from having the coolant drain over it a few times? Each time, I never disconnected the harness. But I suppose I would be getting some short-circuit code for that, wouldn't I?

[old guy]

Before you start replacing parts you should monitor MB-130, 131 and 132 and see how the cooling system is performing. I have outlined the process and what to expect in several previous posts. Unfortunately I don’t have time at work to search them out. If you don’t find them earlier I will find and link them tonight when I get home.

[eljay]

Before you start replacing parts you should monitor MB-130, 131 and 132 and see how the cooling system is performing. I have outlined the process and what to expect in several previous posts. Unfortunately I don’t have time at work to search them out. If you don’t find them earlier I will find and link them tonight when I get home.

No worries. I've seen many of your cooling system troubleshooting posts, so let me do some reading. Unfortunately, I don't have a way to monitor measuring blocks. I'm on my last flush with distilled water and plan to fill in the G12 mix next, so if I have to replace the lower CTS or something else, I'd rather do it now to avoid having to drain coolant again later. I think getting to the lower CTS will be more painful with the bumper back on.

[eljay]

OK. I managed to get my hands on a VCDS and logged 130-131-132 blocks.
Besides temperature, I didn't see any duty cycle values on block 132. 131 showed "Load %|. Is that the thermostat duty cycle?

Here's what I observed:
- fans started right away with the engine.
- For the first time, I got very good heat from the vents at idle and even before the temp gauge reached middle.
- The engine outlet temperature kept going up, while rad temp stayed at 18C.
- 10 mins of idling brought the cluster temp gauge to 12 o'clock and it was rock-steady there the whole time.
- I then experimented and turn off the cabin heater to get the engine temp up quicker to see if the rad starts to go up.
- while I had the cabin heater off, I looked at my rad fans and they were stopped! So, I went back in turned on the cabin heater and checked the fans and guess what, they came on! I repeated this two more times with the same results. Within 5-10 secs of turning cabin heat on/off, the rad fans followed.
- engine temps eventually reached 102C and then I saw the rad temp go to 20C.
- engine temp was fluctuating between 97C and 102C and in that time rad temp went up to 24C.
- when the rad temp started to increased, I saw the Load % on block 131 increase and fluctuate. I saw it as high as 65% and around 35%. The starting value when I started the engine was 3.9%. It eventually returned there.
- the rad temp never went over 24C.
- cabin heat was good the whole time.

So, what can I conclude from the above?
It seems that both coolant temp sensors are working fine, correct? Is my t-stat working too since it did circulate water into the radiator when needed? I was idling the whole time, so I didn't run high engine speed like I would with driving.
The only puzzling thing is the fans coming on full with the engine start. But they do shut off and seems to come on with cabin heater on HI.

[old guy]

Congratulations! You cooling system is operating normally. And yes the duty cycle is the thermostat heater. When you turn the heat on the A/C also becomes engaged and that is what runs the fans. By running the A/C with the heat it helps to dry the air. If you turn off the heat or if you push the econ button with the heat on you should see the fans turn off. Or at least until the FCM decides it's time to start cooling the radiator because the outflow in the lower radiator hose is getting hot.


Edit: And I apologize. Reading back through the last few posts I realize that I didn't look close enough at what you posted. I should have picked up that you had the heat on high from the initial start up. It's one of those things that I just take for granted that when you run the HVAC everything gets engaged. I should have spelled it out a little better. Like either leave the heat off or hit the econ button.

Even then there will be a difference if you have a cooling system DTC. With the A/C on or off the fans will both be on and will both be running in the high speed rather than the low speed mode.

Sorry for the extra work! But look at it this way. You now have a really good understanding on how the system functions!

[eljay]

Congratulations! You cooling system is operating normally. And yes the duty cycle is the thermostat heater. When you turn the heat on the A/C also becomes engaged and that is what runs the fans. By running the A/C with the heat it helps to dry the air. If you turn off the heat or if you push the econ button with the heat on you should see the fans turn off. Or at least until the FCM decides it's time to start cooling the radiator because the outflow in the lower radiator hose is getting hot.


Edit: And I apologize. Reading back through the last few posts I realize that I didn't look close enough at what you posted. I should have picked up that you had the heat on high from the initial start up. It's one of those things that I just take for granted that when you run the HVAC everything gets engaged. I should have spelled it out a little better. Like either leave the heat off or hit the econ button.

Even then there will be a difference if you have a cooling system DTC. With the A/C on or off the fans will both be on and will both be running in the high speed rather than the low speed mode.

Sorry for the extra work! But look at it this way. You now have a really good understanding on how the system functions!

I can't believe you had me do all of this work!!

LOL, I kid I kid and I much appreciate all of your help. I 100% agree that this helped me understand how the cooling system works. Slowly, I'm starting to build some understanding of this internal combustion engine stuff. :)

This certainly saved me throwing parts at it and confirm all is well in the cooling dept.

Thank you old guy!

[diagnosticator]

The two rad fans are controlled from separate controllers. The A/C condenser cooling fan, the smaller right side fan, runs whenever the A/C compressor is active. The condenser fan is controlled by commands from the HVAC control module to the fan control module. The larger rad cooling fan on the left, is controlled by commands to the fan control module from the engine ECU based on inputs from the coolant temperature sensors. If the main rad fan starts up and runs on high speed as soon as the engine is started, is caused by a cooling system malfunction with a DTC stored. The A/C condenser cooling fan does not run fast if there is a cooling system malfunction.