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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0420 - TWC System Low Efficiency >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
  3. Check for exhaust system leak, especially near rear HO2S. Ensure HO2S connectors are secured and not touching exhaust. If a problem is found, go to next step. If no problem is found, go to step 5).
  4. Repair exhaust system as necessary. After repair is completed, go to step 6).
  5. Replace catalytic converter. After repair is completed, go to next step.
  6. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P0420. If scan tool indicates TEST RAN AND PASSED, go to next step. If scan tool does not indicate TEST RAN AND PASSED, repeat step 2).
  7. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.
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