2000 Durango code P1491 diving me nuts

My sisters Durango kicked on a CEL. O2 was weak and had a cooling fan issue. Replaced the 02, that codes gone now, but the P1491 was still there. Found the fan was shorted out and burned the B+ wire going to the relay. Fixed both issues, and now I can use a test light and ground the relay, fan kicks on fine if I make it. When running and you kick the a/c on no fan, pulling the pigtail for the coolant sensor wont kick it on either. All fuses are fin, swapped sme relays around, all them are OK too. Whats going on with this thing?

Did you replace the fan motor itself? You need to check the PCM side of things too. You'll have to try and activate it on and off with a scan tool that is capable of doing that. The PCM pulses the ground to it.

Yep, the fan motor is new and i fixed the burnt wire. Monday I'll get print out of the computer harness out puts and put the scanner on it. Kinda what I was thinking, was just hoping it was maybe a common problem so I aint gotta go diggin in the harness or something.

Check the wiring harness under the battery tray. That is known to be a trouble spot.

I looked there due to some of the battery acid issues. Harness in clean, The fan will work if I ground the relay and thats the harness it goes through.

pcm grounds it internally .. probably fried the pcm good luck dan

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pcm grounds it internally .. probably fried the pcm good luck dan

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Bingo, found that to be the problem. Dang thing is $467 my cost at the dealer and it also has to be programmed for the truck, thats another $85. My sis bout fainted when I told her. Anyone had luck with boneyard computers?