Overheating after driving thirty to forty minutes

  • 2003 GMC ENVOY
  • 4.2L
  • V6
  • 4WD
  • 190,000 MILES
I'm on my last thread here. I put a new water pump, thermostat and serpentine belt on. I had AutoZone read my codes and the only thing that came was a code for the fan clutch wiring harness. New fan clutch was put in about four months ago. The fan never kicks in to high speed once it starts to over heat. Would fixing the wiring harness solve my issue or do I have a blown head gasket? I don't have smoke coming from tale pipe or engine, I also hear the radiator overflow tank making noises as if it is bubbling once it gets past a certain temperature. If you can help that would be great. I'm pretty desperate at this point.
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Wednesday, July 10th, 2019 AT 4:30 PM

1 Reply

If there is a faulty harness or controller that isn't triggering the fan to high speed it would cause it to overheat. The bubbling would be the steam in the system. If you look at the diagram you can see how it is wired. The first items I would check are the connections that is easy if you unplug the fan connector and use a test light connected to battery positive. Touch it to pins A and C, it should light up if they are grounded as they should be. Now use a voltmeter and check for battery voltage to Pin B and for 5 volts at pin E. If those check out then you can reconnect the fan then you need a way to tell the PCM to activate the fan on high, usually you can do that by unplugging the coolant temperature sender shown in the third picture with the engine running. If the fan doesn't respond you either have a problem with the signal feed or the PCM. Unfortunately to test that you need a high end scan tool to trigger the fan on and a meter with a duty cycle measurement to see if the DC changes from low to high as it is toggled.
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Wednesday, July 10th, 2019 AT 8:03 PM

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