2014 Cruze 2.0 diesel...119k on the Odometer. My DIC gave me a warning that my exhaust fluid is poor quality. 100 mile count down to 65mph mode. I have about 4" of DEF left in the tank. Has anyone encountered this before? Do I simply siphon out the def in the tank and refill with new...or is this also a nox sensor problem? Thanks in advance for any help.