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?