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Discussion Starter · #1 ·
I have a problem that's getting more frequent... Used to happen a couple of times a year. The radiator fan will run all the time, from the second I hit the key until I shut off the engine. The resolution was (is) to disconnect the battery and touch the negative to the positive to clear the ECU - then all would be well (for a while, at least).

Now I'm doing it once a week. Doubtful that it's the temperature sensor since clearing the ECU makes it go away..... or not doubtful?

TIA
 

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You do not state that the indicated engine temperature is on the low side of normal. If engine temp is OK, then it could be that the fan is running continuously to compensate for a thermostadt stuck in the closed position, or some other defect in the cooling system. From your description of the problem, I understand that the fan does shut down when the ignition is turned off. If that is true, then the battery should keep it's charge OK. My cooling fan, in our 2006 Volvo S60-2.5T, is relatively quiet, and cannot be heard over the sound of the engine running.
 

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In my experience the fan can be heard over the idling engine when it's on an running. Under hard driving immediately before shutting off the car, or if your cooling temp was at the max point (near or around 220F) then your fan may run for a few minutes after shutting off the car since the temp sensors can continue to work even when the car is off. The fan should not run upon startup however, unless you have your A/C always on. Do you run your A/C constantly? If not, then look into what Eric above suggest and mentions... Good luck!
 

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Discussion Starter · #4 · (Edited)
In my experience the fan can be heard over the idling engine when it's on an running. Under hard driving immediately before shutting off the car, or if your cooling temp was at the max point (near or around 220F) then your fan may run for a few minutes after shutting off the car since the temp sensors can continue to work even when the car is off. The fan should not run upon startup however, unless you have your A/C always on. Do you run your A/C constantly? If not, then look into what Eric above suggest and mentions... Good luck!

No, the fan starts immediately, ("from the second I hit the key") until I shut the car off ("until I shut it off the engine") even when the car is dead cold. It runs 100% of the time. I can make it stop exhibiting the behavior by disconnecting the battery, but then after a week it does it again.

I only disconnect the battery to reset the ECU and make the fan behave normally, not because it is running after shutdown or I fear for the battery.
 

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I wonder if this issue would throw a fault in VIDA... If it begins running constantly after about a week after disconnecting the battery, it sounds like once all of the car's monitors are ready or the ECU is fully ready and settled, that's when it kicks in. I'm just thinking aloud here on this as an observation. Not sure what that could mean or be related to... But I think that if it were the fan itself, it would be doing this upon first startup after resetting the ECU... On our cars, replacing the T-stat includes the temp sensor in the package, and kills 2 birds with 1 stone. Not saying it's either of those but a stuck T-stat sounds plausible but I'm not so sure if it would run the fan immediately upon startup... How about when you turn on the ignition WITHOUT starting the car, does the fan run at that time as well?
 

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-if the temperature sensor is an RTD type, Resistance Temperature Detector, the resistance will climb with the temperature of the engine coolant. If the RTD sensor fails, and there is an open circuit, then the resistance is infinite, and the computer will think that the engine is overheated. If you can locate the temperature sensor, you might be able to measure the resistance with an ohm meter. This is a reasonable course of action. However, I have no explanation for how you can make the problem "go away" for a week or so by disconnecting the battery from the vehicle electronics.
 

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Discussion Starter · #7 ·
-if the temperature sensor is an RTD type, Resistance Temperature Detector, the resistance will climb with the temperature of the engine coolant. If the RTD sensor fails, and there is an open circuit, then the resistance is infinite, and the computer will think that the engine is overheated. If you can locate the temperature sensor, you might be able to measure the resistance with an ohm meter. This is a reasonable course of action. However, I have no explanation for how you can make the problem "go away" for a week or so by disconnecting the battery from the vehicle electronics.
Yeah, that's the part I can't get my head around. Resetting the ECU shouldn't affect a bad temp sensor. I used to be able to make it go away for months.... now it's becoming more frequent. In fact, I leave a 10mm socket in the spare tire well just to reset it.

Aren't Volvos wonderful?

Not to change topic, but the other unique thing my ride does has to do with "auto-up" on the windows. The passenger window, for the period of about a year, would not return to the up position. It would go up to closed, then go right back to where it started. If fully open, it would close, then fully open. If down an inch, it would go up to close, then back an inch. Whatever. One day, it started working perfectly but that same moment the drivers' side started doing it instead (and still does).
 

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From my perspective, it makes sense to use a computer to control something like the operation of a fuel injected engine, but no sense to involve computers in other systems where they are not really needed. When something goes wrong, it is difficult determine the cause, which could be a sensor that is connected to the computer, the computer itself, or the part that does not work, in this case a window with a mind of it's own. In the case of the engine, air temperature, the octane rating of the fuel, engine coolant temperature, driver accelerator pedal position, load, and rpms all would factor into the optimum amount of fuel injected at any point in time. A computer is appropriate for that application. I have a wonky window as well, that sometimes goes up, and then goes right back down, with no command from me. At the moment it is working OK.
 

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Discussion Starter · #9 ·
From my perspective, it makes sense to use a computer to control something like the operation of a fuel injected engine, but no sense to involve computers in other systems where they are not really needed. When something goes wrong, it is difficult determine the cause, which could be a sensor that is connected to the computer, the computer itself, or the part that does not work, in this case a window with a mind of it's own. In the case of the engine, air temperature, the octane rating of the fuel, engine coolant temperature, driver accelerator pedal position, load, and rpms all would factor into the optimum amount of fuel injected at any point in time. A computer is appropriate for that application. I have a wonky window as well, that sometimes goes up, and then goes right back down, with no command from me. At the moment it is working OK.
Yeah, I'm actually kind of amused by the window. And VIDA tells me something about a bad Hall effect switch, so even it doesn't know because if it was the switch how to the problem instantly switch sides????
 

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Hows the charge on your AC? I had mine do this before and turned out to be low on AC charge, i recharged it and fan returned to normal operation.
 

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Hows the charge on your AC? I had mine do this before and turned out to be low on AC charge, i recharged it and fan returned to normal operation.
Same issue with mine. Took it to the dealership and they confirmed it was low on coolant. They tested the system and found no leaks and a completely empty charge, which is weird because the AC worked when I bought it in March. The tech said it was "interesting".
 
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