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Home >> Buick >> 2002 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0401: EGR System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Are there any Manifold Absolute Pressure (MAP) DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Inspect the exhaust system for modification of original installed parts or leaks. Repair the exhaust system as necessary if you locate a problem. Did you find and correct the condition? If yes, go to step  7. If no, go to next step.
  4. Inspect EGR valve gasket and pipe for leaks. If you locate a problem, clean or replace the EGR system components as necessary. Did you find and correct the condition? If yes, go to step  7. If no, go to next step.
  5. Remove EGR valve. Inspect EGR pintle and EGR valve passages for leaks and restrictions. Did you find and correct the condition? If yes, go to step  7. If no, go to next step.
  6. Remove EGR inlet pipe from exhaust manifold. Inspect manifold EGR ports and EGR inlet pipe for a blockage caused by excessive deposits or other damage. Did you find and correct the condition? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  7. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  8. Using scan tool, observe stored information and Capture Info. 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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