Duramax Diesels With SES Light And DTC P0402 - keywords 6.6 air diesel egr engine excessive exhaust flow gas gasket intake leak LMM low Maf noise power recirculation rough valve

This PI was superseded to update model years. Please discard PIP4147B.

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

The customer concern may be SES light on, a loss of power, and DTC P0402. There has been an updated calibration released to address intermittent P0402.

The information in this PI applies to all 2007 model year vehicles. For the 2008 vehicles it only applies to vehicles built before a certain date (break point). Please see build date/break point information in the recommendation section of this PI.

Complete the current SI diagnostics for any trouble code or symptom found.

Completion of diagnostics for P0402 is imperative. Air Charge Cooler leaks, intake duct work leaks, air box/air filter or modifications, EGR gasket leaks, or excessive leaks anywhere in the engine intake system may induce P0402 to set.

If diagnostics are inconclusive there has been a new calibration released for P0402.

Install the updated calibration for P0402 and evaluate repairs.

Note:  When completing SI diagnostics for full system air charge cooler tests remember these important facts:

1. The Charge Air Cooler System will not hold pressure if the air supply is turned OFF. It is normal for air pressure to bleed off.
2. An air leak hissing sound at the EGR valve vent port is normal.
3. An air leak that appears as small bubbles or foaming (when using soapy solution) is normal.
4. Intake Air Heater gaskets that show a small leak or foaming is normal.

Note:  All 2007 model year vehicles may benefit from this calibration if current P0402 diagnostics were inconclusive. Early built 2008 model year vehicles may also benefit from the updated calibration. Please check the build date of the vehicle to verify if an updated calibration is necessary. Vehicles built after the break point already have the new calibration. The break points differ depending on where the vehicle was built. Use the eleventh digit of the VIN to identify plant of origin.

Flint trucks (eleventh digit of VIN is an "F") built after 9/14/07 already have the updated calibration.

Pontiac trucks (eleventh digit of VIN is an "E") built after 9/19/07 already have the updated calibration.

Please follow this diagnostic or repair 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.