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Home >> Pontiac >> 2001 >> Firebird Base, 2D Convertible, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0420: Catalyst System Low Efficiency >> Diagnostic Procedures

Diagnostic Procedures

  1. If powertrain diagnostic system check was performed, go to next step. If powertrain diagnostic system check was not performed, go to POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under DIAGNOSTIC SYSTEM CHECKS. After performing powertrain diagnostic system check, go to next step.
  2. If additional DTCs are set, diagnose those DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If additional DTCs are not set, go to next step.
    NOTE: If A/C is left on, diagnostic may not run.
  3. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn A/C off. Open hood. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function then enter this DTC. Up to 6 tests may need to be completed for test to pas or fail. If test does not pass or fail after 6 tests have ran, go to DIAGNOSTIC AIDS . If scan tool indicates that this test failed this ignition, system is okay at this time. If scan tool does not indicate that this test failed this ignition, go to next step.
  4. Check that three-way catalytic converter is original equipment. Check for converter damage and rattle inside converter. If damage to converter is obvious, go to step  9. If damage to converter is not obvious, go to next step.
  5. Check for exhaust leaks. If leaks are found, go to step  7. If exhaust is okay, go to next step.
  6. Check for damage to HO2S or related harnesses. If damage is found, go to step  8. If HO2S are okay, go to step  9.
  7. Repair exhaust system as necessary. After repairs, go to step  10.
  8. Replace suspect HO2S or harness as necessary. After repairs, go to step  10.
  9. Replace 3-way catalytic converter. After repairs, go to next step.
    NOTE: If A/C is left on, diagnostic may not run.
  10. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn A/C off. Open hood. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function then enter this DTC. Up to 6 tests may need to be completed for test to pas or fail. If test does not pass or fail after 6 tests have ran, go to DIAGNOSTIC AIDS . If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, go to next step.
  11. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no undiagnosed DTCs are displayed, system is okay.
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