Conditions for Running the DTC

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

DTCs P040C, P040D, P041C, P041D or P040F are not set.
The ignition is ON.
The engine is not in diesel particulate filter (DPF) regeneration.
The engine coolant is greater than 50°C (122°F).
The EGR is active for greater than 60 seconds.
The EGR command is greater than 4 percent.
This diagnostic runs continuously when the above conditions are met.