I have a 2001 Nissan Altima. I seem to be having a fan problem. I started noticing that about 2 seconds after I turned the car off, the fans would come back on and run for ~25-30 seconds. I brought it in and my mechanic was thinking maybe a defective thermostat, so we replaced that. It still keeps happening, but now I’ve realized that the fans come back on anytime the car is turned off when the fans are running. If the fans are not running, they won’t come back on. I’ve been trying to pay more attention to what is going on and when I first turn on the car, no fans are on (at least not the high fan, not sure if there are more than 1) After driving around town, the fans will turn on. Normally, I believe the fan should then turn off once the coolant temp gets below a certain level. I let the car sit idling in the driveway for 15 min and the fans never turned off. I took it back to mechanic and repeated the idling for 15 min, fans never turned off. He checked the coolant temp with some sort of sensor and the temps were reading between 166-170 depending on where he aimed his device, so he said the fans should be turning off and it doesn’t seem like the car is overheating.
If he unplugged the temperature sensor, the gauge would go all the way to cold, but nothing changed for the fans, so he didn’t think that was the problem.
He took the fan relays along the edge of the car and swapped them around and nothing changed, so didn’t think it was a relay problem
He removed some sensor on the passenger side on the back part of the engine and the fans got really loud and really fast. When he replace that, the fans would go back to normal until the engine temp got hot enough to turn them on and then they wouldn’t go off again. He’s thinking that sensor might be the problem, but isn’t 100% sure. I think he said this was the cooling fan sensor or switch.
On a side note that may or may not be related. About 5 years ago the water pump broke. It started having the fans on all the time (even from a cold start), that turned out to be a faulty knock sensor. There was a knock sensor code and he replaced the knock sensor and then the fans went back to normal cycling. I didn’t have any problems until early last fall, when I started noticing my current problems. I didn’t worry about it until now, because as it got colder outside, it wasn’t an issue. So outside temperature definitely effects it.
There are no codes this time.