Cooling Fan Not Working, PCM Issue?

[brian m]

I have a 2006 V6. It recently has been overheating. The cooling fan doesn't appear to be turning on. I've tried turning the AC on max but the fan still doesn't turn on.

The wiring harness, plug and cooling fan motor resistor all appear in good order with no signs of burning or wear.

I tested all the relays in the horn slot and all work. Fuses F3 (40A) and F40 (15A) are good.

So, I tried this...

My understanding is the pin 85 on the high speed relay creates a ground when called upon by the PCM. I recently tested pin 85 by connecting a light tester to the positive battery terminal, turned the AC to max (which should initiate a ground), and tested the pin - the light didn't light. That would indicate the ground wasn't created - correct? And that the PCM didn't send the signal? Thus a bad PCM?

Again, all relays and fuses check out.

Any thoughts are greatly appreciated. Thanks

 

[86GT351]

Lift up the fuse panel under hood and check for burnt wires at the relay. It is a known common issue.

 

[brian m]

Thanks! I'll check that out tomorrow. Would burnt wires necessitate the fuse box being replaced? Or can the wire simply be replaced and re-soldered?

 

[jttt424]

Hey man I have the same issue right now I have a 2007 Mustang GT. It’s happened to me once already I did a temporary fix of splicing the first time. Now I’m adding a switch and new wiring wiring and doing away with the factory one. The switch is gonna allow me to turn the fan off and on manually.

 

[brian m]

I'm not sure burnt wires is the culprit. I lifted the fuse box and there's no signs of damage at all. I tested continuity of the wire between the fuse box and the plug with a multimeter and it is good (NO open line).

Any new thoughts? I'm still wondering if it's an issue with the PCM bc there is power to the high speed relay from both fuses pins 87 (40A) and 86 (15A fuse); and the output wire (pin 30) shows no resistance (or OL) between pin and plug. BUT when the AC is on high and the PCM should be establishing a ground at pin 85, no ground seems to exist, as evidenced by test light giving NO light between positive battery post and pin 85 AND between pins 85 and 86. I do however get a light between 87 and 30. I'm guessing if I hard-wired 87 and 30 the fan would run? My assumption is that the relay isn't being activated. The wiring, at least in the pictures, seems OK. What else could it be? Am I mistaken on how this should work? Am I missing something? Thanks for any advice.

 

[brian m]