Coolant Temperature Sensor — Removal, Checking and Installation (Mercedes-Benz C-Class W202)

The temperature sensor measures the coolant temperature and transmits electrical signals to the control unit. The sensor is equipped with an NTC element (NTC – negative temperature coefficient), which decreases its resistance as the temperature increases. If the sensor is faulty, the control unit selects an equivalent value that corresponds to the coolant temperature of the engine heated to operating temperature. At low outside temperatures and a cold engine, this leads to difficulties in starting the engine and to its operation outside the modes.

The temperature sensor is located in the thermostat housing.

Removal

1. Reduce the pressure in the coolant circuit. To do this, open the cap of the expansion tank with coolant.

2. Remove the protective cover (5/3) from the thermostat housing.

3. Remove the plug connector and unscrew the temperature sensor (B11/3).

Examination

1. Suspend the thermometer in a water bath and heat it slowly.



2. Check the resistance of the temperature sensor with an ohmmeter. The measured value is considered normal if it is within the 5% tolerance (see table Temperature sensor resistance).

3. If the temperature sensor does not reach the specified values during measurements, it should be replaced.

Installation

1. Screw in the temperature sensor with a new sealing ring and tighten to 20 Nm.

2. Place the wire connector onto the plug.

3. Warm up the engine and check the tightness of the connections. Check the coolant level again.

Temperature sensor resistance

Temperature	Resistance
+20°C	approx. 2500 Ohm
+30°C	approx. 1700 Ohm
+40°C	approx. 1170 Ohm
+50°C	approx. 830 Ohm
+60°C	approx. 600 Ohm
+70°C	approx. 435 Ohm
+80°C	approx. 325 Ohm
+90°C	approx. 245 Ohm
+100°C	approx. 185 Ohm