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Home >> Saturn >> 2000 >> LS Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Check exhaust system for tightness and leaks between O2S1 and HO2S2. If leak is found, go to next step. If both sensors are okay, ensure engine misfire condition does not exist. Replace catalytic converter.
  3. Repair leak. Test drive vehicle to enable catalyst test. Drive until test either passes or fails this ignition. If test passes, catalyst is okay. If test fails, ensure engine misfire condition does not exist. Replace catalytic converter.
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