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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0420 Or P0430: TWC System - Low Efficiency (Bank 1 & 2) >> Diagnostic Procedures

Diagnostic Procedures

  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. Are any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
  4. Inspect the exhaust system for leak at or ahead of the post HO2S 2, or loose or missing hardware. Repair as necessary. Did you find and correct the condition? If yes, go to step  7. If no, go to next step.
  5. Verify that the correct original equipment three-way catalytic converter is installed. Ensure that the oxygen sensors are properly installed and that the wiring connections are properly retained and not damaged. Repair as necessary. Did you find and correct the condition? If yes, go to step  7. If no, go to next step.
    6. NOTE: Inspect the converter for severe discoloration, indicating a possible catalyst overheating condition. If this condition exists, the cause must be found before the catalyst is replaced.
  6. Replace the catalytic converter. After replacing catalytic converter, go to next step.
  7. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool. Idle the engine at the normal operating temperature. Select the DTC option and the Specific DTC option, then enter the DTC number using the scan tool. Operate the vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the scan tool indicate that this test ran and passed? If yes, go to next step. If no, go to step  2.
  8. 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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