Cooling fan bypass wiring

Discussion in 'Gen 1 & 2 - Electronics & Audio' started by wespiece, Sep 29, 2016.

  1. wespiece

    wespiece SHO Member

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    I am bypassing the CCRM and wiring my fan relay thru my own relay for my buggy swap project. I have it connect like the diagram below but the fan never kicks on when the motor heats up. I have seen temps as high as 220 degrees and still no fan kicking on via the PCM. The fan kicks on when I first turn on the key and start the engine, but then it stops and never seems to start again. I know the relay is good. I know the fan is good. Any ideas on what to test next? I have tried shorting the pins that run to the coolant temp sensor and the relay still does not come on. What am I missing?

    Fan Wiring.PNG
     
  2. Off Road SHO

    Off Road SHO Moderator Staff Member

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    I don't think the PCM reads, a Short across the two wires the same way you and I do.

    For some reason I thought the SHO fan is always hot and the PCM sends a ground to start the fan.

    I don't have my EVTM nearby.

    Tom
     
  3. rubydist

    rubydist SHO Member

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    Tom, that is how he has it in the diagram he posted. From my quick review of the wiring manual, I think that should work.

    So, the pcm could be bad and never turn on the fan, or the temp sensor could be bad and never tell the pcm the temperature, or the wiring between any of that could be bad.
     
  4. Off Road SHO

    Off Road SHO Moderator Staff Member

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    No, that's not what that diagram shows. He still has the battery feed on the battery side of the relay switch and not on the fan side of the switch. The PCM can't pass through enough current to drive fans or fuel pumps so it sends a ground to a fan that already has power through it and almost back to ground.

    Tom
     
  5. Off Road SHO

    Off Road SHO Moderator Staff Member

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    I was wrong, again! The 3.0 and 3.2 SHO's have their CCRM's cooling fan inputs Hot at all times through a 50 amp fuse so you will need at least an 8 guage wire and a 50 amp fuse feeding your new relay. The trip wire for a 3.0 PCM is indeed pin 55 but I don't know what the PCM is sending out on that wire, power or ground. Whatever it is you will have to supply the opposite to your new relay's coil. In other words, if pin 55 sends a 12v signal to one side of your relay's coil, you will need to wire the other side to ground for that relay to be triggered. And vice versa. Did I explain that properly?

    Tom
     

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