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Cooling fan won't run -- Help!

1822 Views 1 Reply 2 Participants Last post by  marylandGT
The cooling fan on my 06 GT doesn’t work. This is a project car and it wasn’t working when I bought it. I’d rather fix it right than just rig the fan to run continuously when ignition is on.

Here's what I have checked out so far. What have I missed or should try? Many thanks!
  • Direct wire from battery: HS fan works, not LS, thus LS resistor might be bad
  • Fan plug is in good condition, no burned terminals.
  • PCM relay is energized when in Run.
  • Shorting HS relay does make the HS fan work.
  • LS fan won’t turn on by shorting relay—12v is at relay, so perhaps resistor is bad.
  • Have not tested LS resistor yet. (though HS runs when relay is shorted)
  • Swapping relays, diode, fuses with tested good—no change, all good.
  • The fan fuse 40A is hot. This was blown when I got it, but replacement doesn’t blow. Odd.
  • Hot at pcm diode and at each fan relay, diode is ok.
  • Temp gauge works properly. Does it get the same temp info as the PCM uses to control the fans?
  • Is there a 2nd temp sensor besides that under intake manifold?
  • The 2 wires for the HS and LS relay control from bussed fusebox to the PCM computer have continuity. (relay sockets to pins 6 & 7 on big PCM plug)
Thus +12V seems to get everywhere it is supposed to. Perhaps the relay control winding ground isn’t being grounded by PCM.

Could the PCM itself be bad?

What have I missed?

The car had some front end damage by a previous owner, so I'm suspicious of wiring problems.

Thanks for your help!
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Here's a thread with good info from other posters on this topic. Hope this helps.
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