Test G: Engine Coolant Temperature Sending Unit

1. Disconnect the YEL/GRN wire from the sending unit and with the engine cold, use an ohmmeter to measure resistance between the positive terminal and the engine (ground). See Fig 1.
2. Check the temperature of the coolant.
3. Run the engine and measure the change in resistance with the engine at operating temperature (radiator fan comes on). See ENGINE COOLANT TEMPERATURE RESISTANCE  table.
   ENGINE COOLANT TEMPERATURE RESISTANCE
   
   

   Temperature	Resistance (Ohms)
   133° F (56° C)	142
   85°-212°F (29°-100°C)	49-32

4. If the readings you get are substantially different from the specifications above, replace the ECT sending unit.

Fig 1: Testing Coolant Temperature Gauge Sending Unit

Courtesy of AMERICAN HONDA MOTOR CO., INC.