Volvo All Engines (2017 Emissions) Fault Code: P021700 PID: EMS Engine Coolant Over Temperature Condition

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) High derate with potentional engine shutdown

Probable cause
1) Extreme driving conditions
2) Coolant thermostat
3) Engine cooling fan
4) Radiator
5) Engine Cooling System
6) Coolant pump
7) Cylinder Head
8) Oil cooler