where is engine coolant temperature sensor located on 2010 Mercedes C300 Sport?

The coolant temperature sensor is located at the rear in the left cylinder head. It is possible the sensor has failed, but it's also possible the engine is not getting to the desired temperature. It would be best to monitor temperature per the sensor versus the actual temperature of the coolant. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops