The Engine Coolant Temperature Sensor is a thermistor. The resistance of the Engine Coolant Temperature Sensor changes inversely to the temperature of the engine coolant. When the coolant is cold, the sensor resistance is high. As the temperature of the coolant increases, the sensor resistance decreases.
The Engine Control Module (ECM) monitors the voltage drop across the Engine Coolant Temperature Sensor.
The coolant temperature signal is used to calculate fuel injection and to evaluate operating conditions of the engine coolant temperature. Examples of conditions that may cause high coolant temperature are: thermostat failure, fan failure, heavy load, high ambient temperatures and radiator blockage.
The sensor’s signal is monitored by the Engine Control Module (ECM).
The engine control module (ECM) will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage if the sensor signal is not within predetermined limits, or the signal is not rational.
Conditions for diagnostic trouble code (DTC):
1) Temperature too high
Observable symptoms
1) A buzzer sounds
2) Engine de-rated
Probable cause
1) Engine cooling fan
2) Fan belt
3) Thermostat
4) Low coolant level
5) Clogged radiator
6) Clogged cooling system
7) Coolant pump drive belt
8) Coolant pump belt tensioner
9) Slipping impeller
10) Poor flow-through in the cooling system
11) Pressure cap, expansion tank
12) Engine coolant temperature sensor
13) Engine control module (ECM)
Conditions for diagnostic trouble code (DTC):
1) The engine coolant temperature (ECT) is above 111??C (232??F)
Observable symptoms
1) High derate with potentional engine shutdown
2) Probable cause
3) Extreme driving conditions
4) Coolant thermostat
5) Engine cooling fan
6) Radiator
7) Engine Cooling System
8) Coolant pump
9) Cylinder Head
10) Oil cooler
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