I am working on a 2011 Chev 6.6 LmL with 75,000 miles on it. It has a DEF Poor Quality message followed by a P207f code and a P20EE.

in reading GM Document on checking DEF specific gravity the statement is said DEF fluid pure concentrate should have specific gravity of 1.31 to 1.384 at 68 degrees.

Question 1 ; Have any of you guys been checking the specific gravity and getting 1.3 or higher reading?

I have done a DPF REGEN it made the NOX 2 sensor read 70% less than the NOX 1 sensor {it would not before REGEN}. It also fixed the NOX 2 sensor where it will go to 0ppm on hard decel.

This condition did not stay corrected for long after a few miles the NOX 2 Senor will not read 70% and the NOX 2 sensor will not go to under 94ppm on hard decel.

The poor fluid quality message has not come back on yet.

Question; How do you determine if you have a defective SCR or contaminated NOX2 ?

Buddy from Georgia