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.

Do you
have the same problem?
Yes
No
Monday, June 4th, 2012 AT 5:27 PM

35 Replies

Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

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

Was this
answer
helpful?
Yes
No
+1
Monday, June 4th, 2012 AT 5:48 PM
Tiny
MIKECARWILE
  • MEMBER

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.

Was this
answer
helpful?
Yes
No
+1
Monday, June 4th, 2012 AT 5:54 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

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.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 6:05 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

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.

Was this
answer
helpful?
Yes
No
-1
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".

Was this
answer
helpful?
Yes
No
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.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 6:26 PM
Tiny
CADIEMAN
  • MEMBER

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.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 6:38 PM
Tiny
MIKECARWILE
  • MEMBER

Rasmataz thats much. Cadieman I did change the cts and they still not come on. Thats why I am here :-)

Was this
answer
helpful?
Yes
No
+1
Monday, June 4th, 2012 AT 6:51 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

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.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 6:52 PM
Tiny
RASMATAZ
  • MEMBER

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

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 6:58 PM
Tiny
MIKECARWILE
  • MEMBER

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 sat could be it (not holding anyone to an answer).

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 7:10 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

There could be a issue with the wires running from the ecm to the coolant temp sensor or other variables. Without seeing the ecm values thats the first place I would start considering the fan turns on when unplugging the coolant temp sensor.I wouldnt scrape it especailly with 80,000 miles on it. Your not bothering us were here to help people fix there cars. We just dont guess when fixing cars. Like I said the tools arent that expensive and whole cheaper then buying another good used cars those are expensive.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 7:16 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

If the stat was opening at too high of a temp then the coolant would get hot enough for the fan to come on?If the stat opened at too low of a temp and the coolant didnt get hot enough for the fans to come then why is coolant boiling over a brand new cap you replaced?

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 7:21 PM
Tiny
MIKECARWILE
  • MEMBER

Saturntech9. Its just fustrating. Did find an infared temp gun on my patio (use it to check bbq temps) 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 analizer and figure out where to hook it up to and get what ever it needs to tell us. Meanwhile I found out that I shopuld be able to drive it till it get sorted out just need to mak esure the a/c runs all the time :-)

Was this
answer
helpful?
Yes
No
+1
Monday, June 4th, 2012 AT 7:24 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

I know its frustrating even the pros like us get frustrated with cars lol.I dont know anything about your bbq thermometer so i cant comment on if it would would work.But where i would measure the temp 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 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

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 7:44 PM
Tiny
CADIEMAN
  • MEMBER

Test the coolant for hydro carbons to check that its not a blown head gasket. They sell a kit at the parts store

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 8:16 PM
Tiny
MIKECARWILE
  • MEMBER

Just ran car for 20 min at ide. Rad hose going to thermostat felt soft and empty but hot. Could the new thermo be bad and not opening properly? Heater works great. Still no fans

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 11:08 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

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.

Was this
answer
helpful?
Yes
No
Monday, June 4th, 2012 AT 11:13 PM
Tiny
MIKECARWILE
  • MEMBER

Been runing fine with a/c as the cooling fans come on. Turn ac off and it spits evertime and my gas gauge goes up to full and stays there no matter how low the tank is.

Was this
answer
helpful?
Yes
No
Thursday, June 14th, 2012 AT 10:58 PM
Tiny
SATURNTECH9
  • EXPERT
  • 30,705 POSTS

How long has the gas gauge been acting up?What codes do you have in the computer?

Was this
answer
helpful?
Yes
No
Please consider a donation if we helped you
Friday, June 15th, 2012 AT 12:06 AM

Please login or register to post a reply.

Related Fan Not Turning On Questions

Recommended articles