DTC P0115 - Engine Coolant Temperature (ECT) Sensor Circuit Malfunction: Condition

WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set if input voltage from ECT sensor is less than .2 volt or greater than 4.9 volts when ignition is turned on. Possible causes are:

ECT sensor malfunction.
Open or short circuit between terminal "A" on ECT sensor and terminal No. 3Q on Engine Control Module (ECM).
Open or short circuit between terminal No. 3AB on Engine Control Module (ECM) and terminal "B" on ECT sensor.