LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> Drive Cycles >> Inspection/Maintenance Exhaust Gas RECIRCULATION System Set Procedure >> Diagnostic Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedure

  1. Perform I/M system check. See INSPECTION/MAINTENANCE SYSTEM CHECK . After performing I/M system check, go to next step.
    2. WARNING: Road test a vehicle under safe conditions and while obeying all traffic laws. Do NOT attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.
  2. Ensure that the vehicle is within the Conditions for Running Test. See CONDITIONS FOR RUNNING . Turn all of the accessories OFF, such as the A/C, blower fan, etc. Start the engine and allow to idle. In order for this test to run, the vehicle must operate in the following conditions:
    • Accelerate at part throttle to 45 MPH and maintain speed for one minute.
    • Four decelerations of 25 seconds each from 45 MPH while the throttle is closed, NO brake application, NO manual downshift, vehicle speed remains above 25 MPH. After each deceleration period, vehicle is returned to 45 MPH under part throttle acceleration and speed is maintained for 15 seconds.
    • Using scan tool, monitor I/M SYSTEM STATUS. Did the EGR System Status update to YES? If yes, go to step  5. If no, go to next step.
  3. Using a scan tool, observe the DTC Information. Does the scan tool indicate any failed DTCs? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  4. Refer to the Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run to complete this test. See INSPECTION/MAINTENANCE SYSTEM DTCS . Using a scan tool, observe the NOT RAN SINCE CODE CLEARED display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the SPECIFIC DTC menu of the scan tool. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC. Repeat the procedure until the scan tool indicates the diagnostic test has run. Repeat procedure for any additional required DTCs that have not run. Using a scan tool, observe the I/M System Status display. Did the EGR System Status update to YES? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  5. Using a scan tool, observe the Emission Related DTC portion of the I/M System Status display. Does the scan tool indicate any Emission Related DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
scientia non olet · About LEMON Manuals