2004-2005 LLY 6.6L Diesel EGR DTCs P0401 or P0404 - keywords idle rough smoke

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

Vehicle may be brought in for SES or MIL light on. Upon inspection of the vehicle, the technician may find EGR DTCs P0401 or P0404.

1. Complete the proper SI diagnostics for the DTCs found.
2. If normal SI diagnostics have been completed and were inconclusive, inspect for any exhaust, air intake, or wiring harness modifications made to the vehicle. Modifications may induce EGR codes.
3. There has been a calibration released to address the concern of intermittent DTCs P0401 and P0404.
4. The new calibration will address DTCs P0401 and P0404 when the codes are set with no engine driveability concerns. If P0401 or P0404 are set and there is a customer concern of low power or black smoke, monitor the EGR valve and MAF sensor readings during the concern. A sticking EGR valve or skewed MAF sensor reading may also cause an intermittent P0401 or P0404 to set.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

(2004-2005 Chevrolet Silverado) and (2004-2005 GMC Sierra)