LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2000 >> Venture Plus >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0420: Catalyst System - Low Efficiency >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Diagnose any other DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Using scan tool, clear DTCs. Ensure A/C is off. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. Test may need to be performed up to 6 times in order to pass or fail. If test has been performed or attempted for more than 6 times and DTC has not passed or failed this ignition cycle, test may be aborting. See DIAGNOSTIC AIDS . If scan tool indicates that DTC ran and passed in this ignition cycle, system is okay. If scan tool does not indicate that DTC ran and passed in this ignition cycle, go to next step.
  4. Ensure TWC is an original equipment part. Check TWC for dents or discoloration caused by excessive heat. Ensure no internal damaged catalyst rattle exists. If a problem is found, repair as necessary. After repairs, go to step  9. If no problem is found, go to next step.
  5. Check exhaust system for leaks, damage, loose or missing hardware. If a problem is found, repair as necessary. After repairs, go to step  7. If no problems are found, go to next step.
  6. Ensure HO2S 2 is securely installed and that harness is not damaged or contacting exhaust. If a problem is found, repair as necessary. After repairs, go to step  8. If no problems are found, go to step  9.
  7. Repair exhaust system. After repairs, go to step  10.
  8. Repair HO2S sensor circuit. After repairs, go to step  10.
  9. Replace TWC. Check for possible engine misfire DTC or engine mechanical problem. After repairs, go to next step.
  10. Using scan tool, clear DTCs. Ensure A/C is off. Start and warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. Test may need to be performed up to 6 times in order to pass or fail. If test has been performed or attempted for more than 6 times and DTC has not passed or failed this ignition cycle, test may be aborting. See DIAGNOSTIC AIDS . If scan tool indicates that DTC ran and passed in this ignition cycle, go to next step. If scan tool does not indicate that DTC ran and passed in this ignition cycle, repeat step  2.
  11. If additional DTCs are present, diagnose affected DTCs. If no additional DTCs are present, system okay.
scientia non olet · About LEMON Manuals