Question about Chevrolet Impala

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Complicated problem here. 2003 Chevrolet Impala had a bad fan. Replaced the fan unit with new. Now, the fans do not come on unless a/c on or coolant temp sensor unplugged. I have replaced coolant temp sensor, all 3 relays, checked fluid level. Ideas?

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  • gforstrom Oct 24, 2010

    The fans were replaced last month. The car has since nearly red-lined a few times. Unplugging the coolant temp sensor has been the only way to avoid serious overheating. If I read your post correctly, it sounds like the pcm is not working correctly. There are no fuses or relays that control the pcm?

  • gforstrom Oct 26, 2010

    I replaced the sensor with a GM dealership part. I replaced the fans with an Autozone part. You mentioned a ground wire. Where should I look for that first?

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  • Master
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A few different things have happened here, either you have a bad ground circuit, you have a brand new bum sensor, or quite possibly the pcm has an issue. If this was aftermarket sensor (Auto Zone or other), it could be faulty. Take it back and have them give you another. This way you don't spend money right off the bat. So let me understand, (1) when you turn on the A/C, fans come on, (2) you unplug the temp. sensor and the fail safe kicks in?!! Run the car until the operating temperature is obtained (220 deg fahreheit) and then turn the heater on making sure that heat is sufficient and no air bubbles are in the system. at 222 deg f, the fans should kick on. Listen for either low or high speed to engage. I am saying this to cover basic steps and work up to further diagnostics. Let me know what you have covered and I can send diagrams and further help.

Posted on Oct 24, 2010

  • Kori Policy
    Kori Policy Oct 26, 2010

    Here are some diagrams but it sounds like you have a PCM issue. Take a look;



    http://repairguide.autozone.com/znetrgs/..." class="h_mi" />

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  • Chevrolet Master
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WELL COOLANT FANS WONT TURN ON UNTIL COOLANT TEMPERATURE 180 190 DEGREES. MOST TIME YOU HAVE TO LET CAR IDLE UNTIL COOLANT FANS TURN ON THE PCM HAS TO RELEARN THE NEW FANS THEN IT WILL RESET.FANS.IF FANS DONT RESET TURN ON YOU HAVE PCM PROBLEM.ITS NOT COMMANDING THE COOLANT FANS TURN ON AT SET COOLANT TEMPERATURE.

Posted on Oct 24, 2010

  • Jonah Oneal Oct 24, 2010

    YOUR PCM HAS A FUSE BUT IT STILL OPERATING OTHER ENGINE CONTROLS LIKE FUEL AND SPARK CONTROL.THE CIRCUIT BOARD OR DRIVER INSIDE PCM NOT COMMANDING THE COOLANT FANS TO TURN ON ANY MORE MEANING PCM FAILURE.TAKE VECHICLE TO GARAGE HAVE PCM SCANNED TO CHECK THE PCM.THAT WAY YOU WONT BE SPENDING TOO MUCH MONEY BUYING A LOT OF UNNECESSRY NEW PARTS.

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