Are you talking about the coolant sensor at the back left side of the motor head? If so I hope you have small hands ;). Use a flat head screw driver to pop the C clip off. Be careful where the O-ring goes. Sometimes it comes off with the sensor, sometimes it stays in the plastic housing, sometimes it falls down onto the trans. It's easier if you put on the O-ring before installing the sensor back into the housing. It allows the ring to seat easier.
