Water Temperature Sender Unit Inspection

Drain the engine coolant. See COOLING SYSTEM SERVICE WARNINGS and ENGINE COOLANT REPLACEMENT .
Remove the ECT sensor.
Place the sensor in water with a thermometer, and heat the water gradually.
Measure the resistance between ECT sensor terminal C and body GND using an ohmmeter.

Fig 1: Identifying Engine Coolant Temperature Sensor Part Side Connector Terminals
Courtesy of MAZDA MOTORS CORP.
- If not as specified, replace the ECT sensor.
Specification

Fig 2: Identifying Engine Coolant Temperature Sensor Specifications
Courtesy of MAZDA MOTORS CORP.