Turn on Fans for LS?

Discussion in 'High Tech Retrofits' started by badazz81z28, Apr 20, 2019.

  1. dave@ztech

    [email protected] Veteran Member Lifetime Gold Member

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    True , then you could eliminate the sensor , with a new one, then if it doesn't work.....
     
  2. 130fe

    130fe Member

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    The GM PCM has fan activation "temps" built in to the tune. What harness are you using? How many fans are you trying to use? Reason I ask is there is a difference between the GMPP LS and other aftermarket LS wiring harnesses when it comes to this.
     
  3. badazz81z28

    badazz81z28 Veteran Member

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    ^^ yes it does. I’m not looking for anything more here than how to trick the computer to turn the fans on because it thinks it’s hot.

    Don’t need any info on how to wire fans.
     
  4. dave@ztech

    [email protected] Veteran Member Lifetime Gold Member

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    He was going to tell you the temp setting, depending on the harness you have.
     
  5. 130fe

    130fe Member

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    Ok, badazz if you know how to wire the fans you could make them come on with/without the pcm SMH. What exactly are you trying to do? Test your fan circuit? Test your pcm function to operate the fan(s)?

    The reason I ask what pcm/harness you are using is because they are different out of the box. The GMPP LS3 harness/PCM controls only one fan (blue wire), it is already fused/post relay that connects straight to the fan + and ground the - wire. It’s factory set ECT is like 207.

    Most other aftermarket LS harness have the ability to control 2 fans (one blue, one green) are trigger wires that provide a ground to “activate” the relay(s). Unless they have been changed, other GM pcms are set to like 220/229 to activate the lo and high fans.

    I know some of the OEM systems have a limp home mode where if you trigger a CEL it will activate at least one fan. Try pulling your MAF plug or something to see if it sets a CEL and energizes a fan.

    But then again you probably knew all of that........
     
  6. 130fe

    130fe Member

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    If you have the ability to change perimeters in your PCM, lower the trigger temp. Other than that, there is no way to “trick” the pcm.
     
  7. badazz81z28

    badazz81z28 Veteran Member

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    4BDEE28D-4888-4443-84C7-446D60404C33.jpeg 4BDEE28D-4888-4443-84C7-446D60404C33.jpeg E49E1E38-E6E6-4667-AA0A-5D736879FAE3.jpeg E6D1253E-2E2D-4A22-82E7-3A79F9A79C36.jpeg The GM performance harness actually has the ability to operate two fans. The blue and green wire from C1 and C3 are there and are actually spliced together at the fuse box wired to control one fan. I left it that way and added another circuit. My wired fan works even with the car off. The GM wiring (way to go GM) actually only works with ignition on. So I can’t simply pull a ECM connector and ground out pin 49 or 54. If I can’t trick the water temp gauge I guess I can always disco my other fan and let it get hot.

    I re-wired this entire harness...I’m not an expert but I know my way around this electrically. That’s why I want to check the relays and validate the wires are in the right spot.
     
  8. 130fe

    130fe Member

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    Get another ECT sensor, connect it to the plug and place the sensor in boiling water. Turn on the ignition and see if your fan works. Not sure if the sensor needs grounding to work though. Just another idea.

    I am going to add one of those PCMofNC fan kits to my GMPP harness. Currently have another one (entropy) installed but I really want two fans AND my pcm to control them. Did you add the bump kit they sell?
     

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