Xterra sat for a while at the mechanic's for AC work. As I drove away, the Service Engine Soon light came on throwing code P0720 - Output Shaft Speed Sensor fail. There doesn't seem to be a lot of info on the net about this sensor. I replaced what I believe to be the sensor. It's the last sensor on the transfer case (because 4wd). Advanced Auto Parts had the correct match with part sn7152. After replacing the sensor and clearing the code, the light and code came back on after a short drive. Any guesses? I'm trying to track down a connector to replace that now. *Neither the tranny nor spedo is having any issues, but the code needs to go away for emissions testing.