Some 2017-2018 F-Super Duty/2016-2018 F650-750 with 6.7L diesel engines and 2015-2018 Transit with 3.2L diesel engines may exhibit a MIL on with diagnostic trouble code (DTC) P206C in the powertrain control module (PCM). This may be due to incorrect diesel exhaust fluid (DEF) concentration. Prior to performing Powertrain Control/Emissions Diagnosis (PC/ED) pinpoint test RJ, confirm DEF concentration using IDS to monitor REDUCT_CONC_MES. This PID reading may fluctuate between 31% and 34% indicating DEF concentration is correct. A concentration reading below 28% will set P206C and cause vehicle derate. This reading may also be checked using Central Tools Refractometer (CEN3R201) which should indicate a similar percentage as the PID. Low concentration of DEF is not a warrantable condition. If low concentration is suspected, drain fluid and replace with known good DEF before replacing any parts.
