Cooling fans will not come on

Tiny
MIKECARWILE
  • 1999 CHEVROLET MALIBU
  • 80,000 MILES

Changed water pump, thermostat, coolant temperature sensor, flushed system, checked all fuses and relays, bled air from system. Fans come on when A/C is turned on, fans come on when coolant temp sensor is disconnected. BUT will not come on during normal operation without using A/C. Dash gauge works fine and with the needle hits 2 marks above mid way coolant comes out of reservoir tank every time. Any suggestions

First thing I did was to replace the cap. Have no idea as to the temp boil point. What elses is there to replace? I think I've replaced everything possible to include new coolant when it was flushed and pressure checked.

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Monday, June 4th, 2012 AT 5:27 PM

35 Replies

Tiny
SATURNTECH9
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If you unplug the coolat temp sensor and the fans come on you know the circuit is good.I would like to know if the ecm is reading the correct coolant temp. You would need a scan tool that reads live data to check that also a infared temp gun to compare actual temp to what the temp the ecm is seeing and reading

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Monday, June 4th, 2012 AT 5:48 PM
Tiny
MIKECARWILE
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If the ECM isnt reading the correct coolant temp then I asume its a bad ECM?(Bascially its the only part that I havent changed in the cooling system) so I might as well purchase one instead of buying all this test equipment that may tell me its bad? Thanks again.

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Monday, June 4th, 2012 AT 5:54 PM
Tiny
SATURNTECH9
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You missed my point the wiring might be good enough to put the fan into default mode doesnt mean its good enough to read the correct values back to the ecm. When I diagnose a problem I always check everything not guess and start replacing parts. If you want to do that good luck to you with replacing the ecm but iam not telling you its bad or that it should be replaced at this time. If your going to diagnose and repair your car the right way you have to buy tools etc to repair and diagnose it properly. If you need anymore help let me know and I will be more then happy to help you.

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Monday, June 4th, 2012 AT 6:05 PM
Tiny
SATURNTECH9
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Also a cheap scan tool that reads live data is like 50 something on amazon a infared temp gun is 50 or under. Cheaper then a ecm and now you have tools for the time you have a car to work on.

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Monday, June 4th, 2012 AT 6:15 PM
Tiny
MIKECARWILE
  • MEMBER

Okay so then what on earth (that I havent all ready replaced with premium NAPA parts which believe it or not are not expensive vs test equipment that will only be used one time). What parts/wiring harness that havent been replaced would cause this possiblty "wiring might be good enough to put the fan into default mode doesnt mean its good enough to read the correct values back to the ecm".

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Monday, June 4th, 2012 AT 6:15 PM
Tiny
RASMATAZ
  • MEMBER

There are some relays that control the fans. Here are some diagrams that will help you fix the problem.

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Monday, June 4th, 2012 AT 6:26 PM
Tiny
CADIEMAN
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The coolant temp. Sensor and a relay control the fans. If u start and run it with the a/c off. Do the fans turn on? If no start by replacing the cts its cheap. God bless ty for using 2carpros pl try to donate.

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Monday, June 4th, 2012 AT 6:38 PM
Tiny
MIKECARWILE
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Rasmataz thats much. Cadieman I did change the cts and they still not come on. Thats why I am here :-)

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Monday, June 4th, 2012 AT 6:51 PM
Tiny
SATURNTECH9
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If you read up further from his first post cadieman he replaced the coolant temp sensor fans work with ac and when unplugging the coolant temp sensor fans come on in default mode. Now to mikecarwile without without knowing the ecms coolant temp readings we dont know whats supposed to be happening relays being grounded etc. Iam not even going to begin to start throwing guesses at you for parts you can change. Were here to help you diagnose and repair your car not say replace this oh that didnt fixed oh try this now. You have two choices get the correct tools to diagnose and repair your car you can take it in for repair. Its hard enough to help people fix there cars over the internet without being able to test anything test drive the car see wires different parts of the car etc. So when I cant ask you what is the ecm reading verus actual temp makes its really difficult to help you.I dont guess when I repair cars in front of me or helping people to fix them over the internet.

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Monday, June 4th, 2012 AT 6:52 PM
Tiny
RASMATAZ
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You sure its the correct thermostat-remember the CTS reads the engine temperature and the Stat controls the temperature-the computer might not be reading it right therefore not activating the fan relay-I guess your last place is the PCM

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Monday, June 4th, 2012 AT 6:58 PM

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