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Home >> Pontiac >> 2001 >> Aztek Base, FWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> 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 diagnostic system check, go to next step.
  2. Diagnose any other DTCs before proceeding with this test. If no other DTCs are set, go to next step.
  3. Turn ignition on, with engine off. 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. Check 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. 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. Repair as necessary. After repairs, go to step  7. If no problems are found, go to next step.
  6. Turn ignition off. Ensure HO2S 2 is securely installed and that harness is not damaged or contacting exhaust. 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. Turn ignition on, with engine off. 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. Check may need to be performed up to 6 times in order to pass or fail. If test has been performed or attempted for greater 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 DTC resets, go to step  2.
  11. If additional DTCs are present, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no additional DTCs are present, system okay.
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