This bulletin applies to all GM/GMC vehicles equipped with a diesel engine and diesel particulate filter (DPF). The MIL may be on and/or excessive smoke from the tailpipe may occur. DTCs P2002, P226D and/or P244A may be set in the ECM.
P2002 will set if the properly functioning system detects a cracked or broken DPF. This code sets when the ECM detects that the DPF has degraded beyond a calibrated threshold. P226D will set if the system detects that the DPF is missing. The exhaust pressure differential sensor is used to diagnose this failure. This code sets when the ECM detects that the pressure difference over the DPF is less than a set threshold. P224A will set if the exhaust pressure differential sensor lines are disconnected or blocked. This code sets when the ECM detects the DPF exhaust differential pressure sensor is lower than the minimum threshold. A properly functioning DPF should remove most if not all soot particles from the exhaust stream. The following tests should not be performed immediately after a regeneration because of the reduced filtration efficiency of the DPF without any soot in it.
Hold a cheese cloth or equivalent across the opening of the tailpipe. Have an assistant rev the engine to the rev limiter and back to idle. Repeat this a total of 8 times. A failed test will show excessive soot particles on the cheesecloth. These soot particles indicate that the DPF is lo longer able to capture all of the soot particles in the exhaust stream, and needs to be replaced.
