Engine Coolant Temperature (ECT) Sensor

1. Coolant temperature sender is part of ECT sensor. Remove ECT sensor. ECT sensor is located on left side of engine. Place ECT sensor and thermometer in a container of water. Connect ohmmeter between ECT sensor terminals "A" and "B". See Fig 1 .
2. Slowly heat water. Observe resistance reading at specified temperatures. If resistance is not as specified, replace ECT sensor.
3. To check coolant temperature sender portion of ECT sensor, measure resistance between ground and ECT sensor terminal "C". See Fig 1 . Resistance should be 152-242 ohms with sensor temperature at 122°F (50°C). Replace ECT sensor as necessary.

Fig 1: Identifying ECT Sensor Terminals

Courtesy of MAZDA MOTORS CORP.