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Home >> Chevrolet >> 2001 >> Impala LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0420: Catalyst System Low Efficiency >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
  2. Diagnose any other DTCs present before proceeding. If no other DTCs are present, go to next step.
  3. Using scan tool, clear DTCs. Ensure A/C is off. Start and warm engine to normal operating temperature for a least 10 minutes. Run engine at more than 1500 RPM for an additional 5 minutes. (One minute for each additional attempt at 1500 RPM on same key cycle). Vehicle may be driven for 5 minute run time. Fully open hood. Operate vehicle within code enable criteria. 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 aborted. 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 problem was found, repair as necessary. After repairs, go to step  9. If problem was not found, go to next step.
  5. Check exhaust system for leaks, damage, loose or missing hardware. If problem was found, repair as necessary. After repairs, go to step  7. If problem was not found, go to next step.
  6. Ensure HO2S 2 is securely installed and that harness is not damaged or contacting exhaust. If problem was found, repair as necessary. After repairs, go to step  8. If problem was not 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 for a least 10 minutes. Run engine at more than 1500 RPM for an additional 5 minutes. (One minute for each additional attempt at 1500 RPM on same key cycle). Vehicle may be driven for 5 minute run time. Fully open hood. Operate vehicle within code enable criteria. 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 aborted. 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  4.
  11. Using scan tool, observe stored information. If scan tool displays any DTCs that have not been diagnosed, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not display any DTCs, system is okay.
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