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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 102 (Engine Controls - Self-Diagnostics - 3.5L) >> Diagnostic Tests >> DTC P0420: Catalyst System Low Efficiency >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue and 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. If any other DTCs are set, diagnose DTCs before continuing with this test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
    NOTE: In the following step, if A/C clutch cycles, diagnostic test will abort.
  3. Using scan tool, clear DTCs. Turn A/C off. Start engine. Ensure engine is at normal operating temperature. Operate vehicle within conditions for running the DTC. See CONDITIONS FOR RUNNING DTC . If more than 6 tests have been attempted and DTC has not passed or failed this ignition cycle, the test may be aborting. See DIAGNOSTIC AIDS . The diagnostic test may need to be completed up to 6 times in order to pass or fail. Does scan tool indicate the DTC ran and passed this ignition cycle? If yes, system is okay. If no, go to next step.
  4. Ensure original 3-way catalytic converter is installed correctly. Check catalytic converter for damage, severe discoloration or tampering. If any problems are found, go to step  7. If no problems are found, go to next step.
  5. Check exhaust system for leaks, damage, and loose or missing hardware. Repair exhaust system as necessary. After repairs, go to step  8. If exhaust system is okay, go to next step.
  6. Ensure oxygen sensors are properly installed and wiring and connections are okay. If any problems are found, repair as necessary. After repairs, go to step  8. If no problems are found, go to next step.
  7. Replace catalytic converter. After repairs, go to next step.
    NOTE: A misfire condition may damage replacement catalytic converter. Check for misfire condition and repair as necessary before replacing catalytic converter.
  8. Turn ignition off. Reconnect all disconnected connectors. Using scan tool, clear DTCs. Turn A/C off. Start engine. Ensure engine is at normal operating temperature. Operate vehicle within conditions for running the DTC. See CONDITIONS FOR RUNNING DTC . Diagnostic test may need to be completed up to 6 times in order to pass or fail. If more than 6 tests have been attempted and DTC has not passed or failed this ignition cycle, test may be aborting. See DIAGNOSTIC AIDS . If DTC runs and passes, go to next step. If DTC resets, go to step  4.
  9. Using scan tool, check for any other DTCs that are set. If no other DTCs are set, system is okay. If any other DTCs are set, repair DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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