1999-2000 Models

Disconnect the YEL/GRN wire (A) from the coolant temperature gauge sending unit (B).

Fig 1: Disconnecting YEL/GRN Wire From Coolant Temperature Gauge Sending Unit
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Using an ohmmeter, measure the change in resistance between the positive terminal (C) and the engine (ground) with the engine cold and with the engine at operating temperature.

Fig 2: Measuring Change In Resistance Between Positive Terminal (C) & Engine (Ground) With Engine Cold & With Engine At Operating Temperature
Courtesy of AMERICAN HONDA MOTOR CO., INC.
If the obtained readings are substantially different from the specifications above, replace the sending unit.