Cutlass Supreme Coolant Fans Won't Turn On


1994 OLDSMOBILE CUTLASS SUPREME. Engine size = 3.1L
Question: I'VE BEEN TOLD THAT MY COOLANT FANS AREN'T RUNNING WHEN THE ENGINE GETS UP TO TEMPERATURE. THE FANS DO RUN BUT AREN'T COMING ON AUTOMATICALLY. THE FAN RELAYS ARE GOOD. WHAT SENSOR TELLS THE RELAYS TO TURN ON THE FAN.

I KNOW ONE FAN DOESN'T COME ON UNLESS THE A/C IS SWITCHED ON BUT RIGHT NOW I HAVE AN A/C LEAK BUT I SHOULD HAVE AT LEAST ONE FAN COME ON.

Answer: The radiator fans come on at different times. One is for low, both on is for high. The low fan turns on at approx. 226 Degrees F. The high at about 255. They are controlled by the ECM (computer) from a reading it gets from the coolant temperature sensor. The coolant temp sensor may be faulty, or the ECM or the wiring between the two. A scan of the system with a scanner that shows live data may give you a clue to where the problem is. If there is an open circuit in the sensor or wiring, it would show the temperature as -40 F. If it shows fine, then you may have a problem with the computer or the wiring to the relays. You would need a schematic and a test light to diagnose this system, which can get a little tricky.


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  • Guest - O

    My fans stayed running when car was off for days. Swapped out computer from junkyard fans OK so its in computer Except it runs rough so bought reman computer had flashed hopefully I am good to go we see later today. Plus all my codes went away with different computer . So computer hada to be failing for most of my issues as I did test relays ect...schematic shows stuff inside computer we cant test.

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