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This PI was superseded to update Recommendation/Instructions. Please discard PIP4147A.

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.

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

Completion of diagnostics for P0402 is imperative. Air Charge Cooler leaks, intake ductwork 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 is 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 engine will not hold pressure if the gage valve is turned 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 is normal.
4. Intake Air Heater gaskets that show a small leak or foaming is normal.

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.