Toyota Repair: 1990 Toyota 4x4 V6, AT Extended cab truck, toyota 4x4, temp gauge

Question
My code reads 22, which is water temp. circuit. Should I replace the water temp sensor first, and where is it located.When driving,the check engine light comes on and the transmissions seems to shift hard, and shift up and down on its own. The check engine light does not stay on all the time. Also, when I checked the codes, the overdrive off light flashed dimly when the check engine light was flashing. Any ideas?  

Answer
The water temp sensor is located on the rear of the engine near the firewall, it's on a housing that has a few other sensors on it as well, make sure you replace the sensor for the ECU not the one for the temp gauge, the ecu sensor has two wires, the gauge sensor has only one.