Diagnostic Aids

WARNING: This page is about a different car, the 2007 GMC Sierra, 2007 GMC Cab & Chassis Sierra, 2007 Chevrolet Silverado, and 2007 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The use of 500 ppm sulfur, non-road diesel fuel containing red dye, or the continuous use of non ultra low sulfur fuel may be a possible contributor to the degradation of metals in the DOC. A degraded DOC will not light off, and properly maintain the necessary heat required to completely regenerate the particulate filter.
If EGT sensor 1 (before the DPF) is slow to respond to exhaust gas temperature changes, or sticks in range, this DTC may set.