Hi, the last light I need to turn off is my 4wd light, it flashes intermittently in 2wd. 4wd engages perfectly and shifts into 2wd fine. The mechanic I had the truck at for almost 2 wks to turn off brake/abs light didn't correct this, just wanted to wash my hands of that guy. Trying to figure this out,I took what looks to be a sensor out and it looked clean, what else could cause this, do I need to replace the sensor?