On my xc90 I have replaced the engine cooling fan 2 times and have hit a snag. I was going to order the coolant temp sensor for the computer but before I order it from fcp I wanted to make sure I order the right part. The fan stopped working so I replaced it and it worked for about 6 months and stopped working again so I replaced it again in April. this time the fan stopped after 2 months but will function "most" of the time when I turn on the A/C but never when the engine temp gets high. I have ohmed the sensor wire that goes to the ECM and the fan has proper voltage. One strange thing about the fan is when it tries to come on the fan will rock back and forth a few times. sometimes it will come on and sometimes it will just stop and do nothing, but if I unplug the fan for a short while and plug it back it will start up. Kinda stumped as to what needs to be ordered or replaced. any help would be very appreciated