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Engine cooling fans will not come on?

Tiny
MIKECARWILE
  • MEMBER
  • 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 temperature sensor is disconnected. But will not come on during normal operation without using A/C. Dash gauge works fine and with the needle hits two 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 temperature boil point. What else is there to replace? I think I have 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

45 Replies

Tiny
SATURNTECH9
  • MECHANIC
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If you unplug the coolant temperature 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 temperature. You would need a scan tool that reads live data to check that also a infrared temperature gun to compare actual temperature to what the temperature 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 is not reading the correct coolant temperature then I assume it is a bad ECM? (Basically its the only part that I have not changed in the cooling system). So I might as well purchase one instead of buying all this test equipment that may tell me it is 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 does not mean it is 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 I am not telling you it is bad or that it should be replaced at this time. If you are 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 fifty something on Amazon an infrared temperature gun is $50.00 or under. Cheaper then an 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
  • 14 POSTS
Okay so then what on earth (that I have not 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 have not been replaced would cause this? Possibly wiring might be good enough to put the fan into default mode does not mean it is 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
  • MECHANIC
  • 75,992 POSTS
There are some relays that control the fans. Here are some diagrams that will help you fix the problem.
Images (Click to make bigger)
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Monday, June 4th, 2012 AT 6:26 PM
Tiny
CADIEMAN
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The coolant temperature sensor and a relay control the fans. If you start and run it with the A/C off do the fans turn on? If no start by replacing the CTS, it is cheap. God bless. Thank you for using 2carpros.
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Monday, June 4th, 2012 AT 6:38 PM
Tiny
MIKECARWILE
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  • 14 POSTS
Rasmataz that is much. Cadieman I did change the CTS and they still not come on. That is 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 temperature sensor fans work with AC and when unplugging the coolant temperature sensor fans come on in default mode. Now to Mikecarwile without without knowing the ECM's coolant temperature readings we do not know what is supposed to be happening relays being grounded etc. I am 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 did not 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. It is 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 cannot ask you what is the ECM reading versus actual temperature makes it really difficult to help you. I do not 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 it is 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
Tiny
MIKECARWILE
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Rasmataz, I will compare Napa part number from stat box I still have against what Napa says should be the correct part number. So defective/wrong new stat could be it (not holding anyone to an answer).
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Monday, June 4th, 2012 AT 7:10 PM
Tiny
SATURNTECH9
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There could be a issue with the wires running from the ECM to the coolant temperature sensor or other variables. Without seeing the ECM values. That is the first place I would start considering the fan turns on when unplugging the coolant temperature sensor. I would not scrape it especially with 80,000 miles on it. You are not bothering us we are here to help people fix there cars. We just do not guess when fixing cars. Like I said the tools are not that expensive and whole cheaper then buying another good used car, those are expensive.
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Monday, June 4th, 2012 AT 7:16 PM
Tiny
SATURNTECH9
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If the stat was opening at too high of a temperature then the coolant would get hot enough for the fan to come on? If the stat opened at too low of a temperature and the coolant did not get hot enough for the fans to come then why is coolant boiling over a brand new cap you replaced?
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Monday, June 4th, 2012 AT 7:21 PM
Tiny
MIKECARWILE
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Saturntech9, it is just frustrating. Did find an infrared temperature gun on my patio (use it to check bar-b-q temperatures) this should work? No just got to figure out whet to point it at on the car. Will look at local shops for real time analyzer and figure out where to hook it up to and get what ever it needs to tell us. Meanwhile I found out that I should be able to drive it until it get sorted out just need to make sure the A/C runs all the time. :-)
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Monday, June 4th, 2012 AT 7:24 PM
Tiny
SATURNTECH9
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I know it is frustrating even the pros like us get frustrated with cars, lol. I do not know anything about your bar-b-q thermometer so i cannot comment on if it would would work. But where I would measure the temperature would be on the head right where the upper hose attaches. Here is a link to a scan tool that reads live data locally you will probably spend way over $100.00 for one:

http://www.amazon.com/AutoLink-CAN-OBDII-Code-Reader/dp/B001R5K2W8/ref=wl_it_dp_o_pC_nS_nC?ie=UTF8&coliid=I550IMQ2KTG23&colid=18P9GG85XVI37
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Monday, June 4th, 2012 AT 7:44 PM
Tiny
CADIEMAN
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Test the coolant for hydro carbons to check that it has not a blown head gasket. They sell a kit at the parts store.
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Monday, June 4th, 2012 AT 8:16 PM
Tiny
MIKECARWILE
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Just ran car for twenty minutes at idle. Radiator hose going to thermostat felt soft and empty but hot. Could the new thermostat be bad and not opening properly? Heater works great. Still no fans.
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Monday, June 4th, 2012 AT 11:08 PM
Tiny
SATURNTECH9
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Like I said before if the thermostat was opening too late or even not at all the fan should turn on before it boils overs.
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Monday, June 4th, 2012 AT 11:13 PM
Tiny
MIKECARWILE
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  • 14 POSTS
Been running fine with A/C as the cooling fans come on. Turn A/C off and it spits every time and my gas gauge goes up to full and stays there no matter how low the tank is.
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Thursday, June 14th, 2012 AT 10:58 PM
Tiny
SATURNTECH9
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How long has the gas gauge been acting up? What codes do you have in the computer?
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Friday, June 15th, 2012 AT 12:06 AM

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