Mercedes ML exhaust sensor error.. HELP

[davidcarr1980]

Hi Guys I need some help my wife 2013 ML 350. Is showing error code P2470 EGT sensor circuit low bank 1 sensor 4 and P246F EGT circuit range performance bank 1 sensor 4. I had another sensor changed at Mercedes at a cost of £500 and the error messages cleared for a month now this sensor is faulty.
Can this be removed and cleaned or do I require this sensor to be replaced?. I find it strange 2 sensors fail with in a month of each other. Any help would be great.
Thanks