Engine Coolant Temperature Sensor: Miata

ECT Sensor Testing Procedure  Remove ECT sensor. ECT sensor is located on left side of engine. Place ECT sensor and a thermometer in a container of water. Connect ohmmeter between ECT sensor terminals "A" and "B". See Fig 1 . Slowly heat water. Observe resistance reading at specified temperatures. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR SPECIFICATIONS  table. If resistance is not as specified, replace ECT sensor. If sensor resistance is within specification, check wire harness for short or open circuits. Repair or replace as necessary.

Engine Coolant Sender Testing Procedure  To check coolant temperature sender portion of ECT sensor, measure resistance between ground and ECT sensor terminal "C". See Fig 1 . Resistance should be 160-230 ohms with sensor temperature at 122°F (50°C). If engine coolant sender resistance is within specification, check wire harness for short or open circuits. Repair or replace as necessary.

Fig 1: Identifying ECT Sensor Terminals (Miata)

Courtesy of MAZDA MOTORS CORP.