Mercedes-Benz W201 coolant temperature sensor: location, testing and faults
Mercedes-Benz W201 where is the coolant temperature sensor and what does it do?
The sensor is at the front of the cylinder head, near the thermostat housing, and it has two or four pins. It tells both the fuel injection and the ignition the engine temperature. Coolant runs out when it is removed, about half a litre.
Mercedes-Benz W201 what are the symptoms of a faulty temperature sensor?
Poor cold starting, revs dropping and stalling, and uneven running. The sensor can also show a good resistance when cold but be wrong when warm, so a failure to start when warm can be caused by it. The temperature gauge reading may stay fixed.
How is the Mercedes-Benz W201 temperature sensor tested?
Disconnect the connector and measure the resistance between the pins with a multimeter. When cold, the resistance should be in the kilohm range (for example 2500–4000 ohms), and when warm, at about 80 degrees, about 300 ohms. On a four-pin sensor, measure across the pins. If the value is wrong, replace the sensor; the colour and part number of the new one must match the old one.