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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1660 (Engine Control System & Fuel System - 6.6L (LMM) - DTC P02E8 To DTC P1247) >> DTC P0401 or P0402 >> Circuit/System Verification

Circuit/System Verification

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: Occasionally, when using an EGR device control, Engine Reduced Power and Clean Exhaust Filter messages may occur after a short delay when commanding large EGR positions. The messages are a result of ECM protecting hardware during device control mode. No DTCs will be stored and the Diesel Particulate Filter does not need to be service cleaned. Exiting device control will restore normal function.
  1. Verify if DTC P003A, P0101, P0403, P0405, P0406, P046C, P0698, or P0699 are not set.
  2. Ignition ON, observe the Desired EGR Position and the EGR Position Sensor parameters. With a scan tool, command the EGR solenoid to 20 percent in 5 percent increments. The Desired EGR Position and the EGR Position Sensor parameters should respond and remain within 3 percent of each other with each command.
    • If greater than the specified range or the EGR Position Sensor parameter does not respond and remains stationary, replace the EGR valve and gaskets.
  3. Engine running at idle speed, perform the following:
    • With a scan tool, command the EGR solenoid to 40 percent.
    • Increase the engine speed to 2,500 RPM. The engine should run rough.
  4. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
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