P207F

P207F is the reductant quality code - the ECM compares upstream and downstream NOx sensor readings during steady-state cruise and concludes the DEF being dosed is either diluted, contaminated, or not actually 32.5 percent urea. Cheapest-first ladder: before anything else, refractometer-test the DEF in the tank (must read 32.5 plus or minus 0.7 percent urea), and inspect for water dilution, diesel fuel contamination (a common owner mistake), or expired DEF that has decomposed. Caveat: P207F has a regulated inducement cycle that cannot be cleared by simply draining and refilling DEF - the ECM requires a series of validated good-quality cruise cycles before lifting the inducement.

Vehicle-specific patterns: 2011 to 2014 Ford 6.7L Powerstroke set P207F constantly from contaminated DEF or a known failing DEF quality sensor; 2010 to 2016 Mercedes Sprinter BlueTEC fail from DEF crystallization on the dosing line; 2009 to 2014 VW/Audi Q7/Touareg 3.0 TDI BlueTEC set P207F when owners use windshield washer fluid by mistake; 2011 to 2016 Duramax LML throw the code from a stuck-open dosing valve over-dosing then setting quality fault. Estimated repair: $40 to $1,800.