2002 Mercedes Benz C230 P0131 ck eng lt code

This code indicates a faulty O2 sensor as the voltage reading is lower than specified. Replacing the sensor should fix the problem. However, if this is the same O2 sensor as you replaced prior then you may want to look at other possible causes. Bank 1 Sensor 1 is the first O2 sensor (pre-catalyst) and if this is failing this quickly I would look at possible "rich" running condition which will take out O2 sensors fast due to the sensor being exposed to unburned fuel. Also not if a rich condition is causing this then you may see your catalyst and rear O2 sensor go out for the same reasons.