Exhaust Fluid Quality Poor

2012 Chevrolet 3500 6.6L Duramax Diesel EXHAUST FLUID QUALITY POOR I determined that the downstream NOx sensor was bad. When you're driving and take your foot off the accelerator after moderate acceleration, both NOx sensors should drop to 1 or 0 while the fuel is cut off. The downstream sensor was stuck at 14 or 15 ppm. After replacing the NOx sensor, I had to do a reductant fluid quality test. The instructions on my scanner were wrong for the exhaust fluid quality test (RFQT). The ECM won't start an RFQT unless the NOx sensors have been warmed up and are sending good data. If the computer won't run the test and the exhaust is completely warmed up, then try a two minute key off before re-trying. The fix was running a manual DPF regen, followed by the RFQT (reductant fluid quality test). If the reductant quality has been running for an hour, then it probably won't finish. Related documents: GM Service Information document ID 2522607. GM Service Bulletin PIP5007E https://static.nhtsa.gov/odi/tsbs/201... GM Service Bulletin PI1214A.