Engine Coolant Temperature (ECT) Sensor

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Engine Coolant Temperature Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

The engine coolant temperature (ECT) sensor checks the temperature of the engine coolant. The temperature of the engine coolant is required so that the engine control module (ECM) can regulate:

the injection period
the idle speed
the engine cooling fan (FC)
the ignition advance
engagement and disengagement of the A/C compressor
diagnostic functions.

The sensor is a negative temperature coefficient (NTC) type which is supplied with power from the control module (signal) and is grounded in the control module.

The resistance in the sensor changes depending on the temperature of the coolant. Depending on the resistance in the sensor, a voltage (signal) is transmitted to the Engine Control Module (ECM). At 0 °C, the voltage is approximately 4.0 V. At 100 °C the voltage is approximately 0.5 V. Low temperature results in high voltage (high resistance), high temperature in low voltage (low resistance).

The engine coolant temperature (ECT) sensor is located beside the thermostat.

The engine control module (ECM) can diagnose the engine coolant temperature sensor. The sensor value can be read off using VIDA.