# Crazy fans



## Agoudine (Feb 19, 2005)

Cooling fans turn on and off for shirt periods (about 10 seconds) when engine is absolutely cold. It starts immediately after I start the engine in the morning. I don't think fans should be on with cold engine.
I suspect the coolant temperature sensor,but manual does not tell how to check and even locate it.
Please,tell me what do you think?


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## jserrano (Oct 27, 2004)

The coolant sensors are on the backside of the engine, passenger side.

Here is a picture,










The top sensor with two pins is for the ECU. The bottom one pin with one terminal is for the temperature gauge.

Disconnect the sensor and the fans should never come ON. If it does, then it points to a cooling fan relay or ECU problem.


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## Agoudine (Feb 19, 2005)

Thank you for the excellent reply and picture. 
I found the sensor and and did the test:
disconnected the wire from sensor and turned on the engine.
The fans turned ON immediately and did not turn off even after I stoped the engine and continued to work for pretty long time until I disconnected the battery! Then I reconnected everything and started engine again: fans turned on immediately and turned off with the engine.
What can I do to find out if it's a fan switch or ECU and fix it?
Besides it looks like one fan is turning faster then the other.


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## jserrano (Oct 27, 2004)

Don't forget that if the AC switch is ON or the ECU "thinks" it is ON it will fire up the cooling fans. Your AC compressor would've been running and you should had felt the cool blast of air. But just in case, remove fuse #6 (10 amps) which powers the pushbutton heating/cooling controller on the front dashboard.

Frankly, it sound like the ECU is causing the problem. You need to confirm the voltage at the backside of the ECU. The light green wire is for the HI speed and the light green/red for the LO speed. If the voltages are about 12V then it points to a problem outside the ECU. Otherwise, the ECU is likely to be bad.


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## Darktide (Jul 29, 2004)

I have a 2000 NIssan Altima... i'm having the same problem. Thanks for the info.


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## 2000SE (Oct 28, 2002)

Defrost can also cycle the fan/AC compressor. 
Sensors/relays don't last forever. They are cheap enough to replace. 
Also, make sure your coolant is topped off.


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## KDragon (Oct 9, 2006)

Sorry for digging up an old thread but I'm having a similiar issue i check the voltage from the ECM to the sensor and it reads 5.90 volts i should be at 5 is this to high? also I cant check the resistance on the ECTS because of its location and i don't have any teflon tape to re wrap the threads if i take it out. Any one got any tricks for checking it?:newbie:


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## KDragon (Oct 9, 2006)

DOH I just reread the first post my problem seems to be that the fans never come on even if its 80+ outside and driving for an hr+ mixed city and hwy.

The only time they turn on is if i disconnect the temp sensor then i also get a CEL light. I just replaced the sensor and theres no difference.

However if i put a 150 ohm resistor in the place of the sensor the fans fire right up w/out the CEL. The only thing i can think is its just not getting hot enough.


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