Circuit/System Description

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.

The particulates in the exhaust gases (solid particles in the exhaust exhibited as black smoke) are collected by the diesel particulate filter (DPF). When the filter becomes saturated with particulates, they are oxidized by incineration. We will refer to this incineration process as regeneration. When an active regeneration is commanded with the engine control module (ECM) a different engine calibration strategy is used to elevate the exhaust gas temperatures. The first event is to heat up the oxidation catalyst (DOC). Secondly the particulate filer temperature is elevated. These elevated exhaust gas temperatures incinerate the soot accumulated in the particulate filter.

The ECM will command a regeneration based on a calculated soot model. The soot model calculations are based on a number of different factors including:

Distance since last DPF regeneration
Fuel used since last DPF regeneration
Engine run time since last DPF regeneration
Differential pressure sensor values

The ECM monitors the DOC and DPF temperatures with inputs from two exhaust gas temperature (EGT) sensors 1 and 2, located before and after the exhaust particulate filter. The ECM also monitors the differential back-pressure in the filter by a differential pressure sensor.

If the time between completed DPF regenerations become too infrequent, this diagnostic will fail.