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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 92 (Engine Controls - Self-Diagnostics - 6.6L Diesel) >> Diagnostic Tests >> DTC P0401: EGR System - Insufficient Flow >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Is DTC P0404, P0405, P0406, P0489, P0490, P1404, P2141, P2142, P2144, or P2145 also set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Disconnect the EGR valve vacuum hose. Install a vacuum gauge on the vacuum hose. Start and idle the engine. Command the EGR System Seal to 100 percent with a scan tool. Is the vacuum more than 15 in. Hg? If yes, go to next step. If no, go to step  6.
  4. Connect a vacuum pump to the EGR valve. Apply 15 in. Hg. Does the EGR valve hold steady vacuum? If yes, go to step  8. If no, go to next step.
  5. Test for the following conditions:
    • Restricted vacuum hose between the vacuum pump and the EGR throttle valve vacuum control solenoid.
    • A restricted EGR throttle valve vacuum control solenoid.
    • Plugged EGR ports.
    • Exhaust system leaks.
    • Exhaust system restrictions.
    • Exhaust system modifications.

    Did you find and correct the condition? If yes, go to step  9. If no, see DIAGNOSTIC AIDS .

  6. Repair the leak or restriction in the vacuum hose between the EGR valve and the vacuum sensor. After repairs, go to step  8.
  7. Replace the EGR valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION. After repairs, go to next step.
  8. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC option using the scan tool. Idle the engine at the normal operating temperature. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool. Operate the vehicle within the Conditions for Running this DTC, if applicable. Does the scan tool indicate that this test failed? If yes, go to step  2. If no, go to next step.
  9. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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