Mercury MerCruiser D2.8L D-Tronic Service Manual page 486

DESCRIPTION
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The Engine Coolant Temperature (ECT) Sensor is a thermistor (a resistor which changes
value based on temperature) immersed in the engine coolant stream. Low coolant
temperature produces a high resistance, while high temperature causes low resistance.
The ECM supplies a fixed current to the ECT through a resistor in the ECM and measures
the voltage. The voltage will be high when the engine is cold, and low when the engine is
hot. By measuring the voltage, the ECM knows the engine coolant temperature. Engine
coolant temperature affects most systems the ECM controls.
A failure in the ECT circuit should set Code P0115. Remember, this code indicates a failure
in the coolant temperature sensor circuit, so proper use of the chart will lead to either
repairing a wiring problem or replacing the sensor.
Page 5A-20
a - ECT Sensor
b - Harness Connector
c - Locking Tab
b
c
a
SERVICE MANUAL NUMBER 22
75341
90-860074--1 FEBRUARY 2002