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DTC P0420: 1/1 Catalytic Converter Efficiency: Testing

NOTE: If an O2 sensor DTC is also set, diagnose O2 sensor DTC before proceeding. Also, check for contaminants that may have damaged O2 sensor and catalytic converter such as contaminated fuel, unapproved silicone, oil and coolant.
  1. Turn the ignition on. With the DRBIII(R), read DTCs. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  7 .
  2. Inspect the catalytic converter for the following damage:
    • Dents and holes.
    • Severe discoloration caused by overheating the catalytic converter.
    • Catalytic converter broken internally.
    • Leaking catalytic converter.

    Were any problems found? If yes, replace the catalytic converter and repair the condition that may have caused the failure. If no, go to next step.

  3. Start the engine. Allow the engine to idle. Inspect the exhaust system for leaks between the engine and the 1/1 O2 sensor. Inspect the exhaust system for leaks between the engine and the 1/2 O2 sensor. Are there any exhaust leaks? If yes, repair or replace the leaking exhaust parts as necessary. If no, go to next step.
  4. Check the exhaust for excessive smoke caused by an internal problem in the engine. Is a engine mechanical condition present? If yes, repair the engine mechanical condition as necessary. If no, go to next step.
    5. NOTE: A new 1/2 O2 sensor along with an aging 1/1 O2 sensor may cause the DTC to set.
  5. Review repair history. Has the 1/2 O2 sensor been replaced without replacing the 1/1 O2 sensor? If yes, replace the 1/1 O2 sensor as necessary. If no, go to next step.
  6. There are no possible causes remaining, replace catalytic converter.
    7. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
    NOTE: Check for contaminants that may have damaged O2 sensor such as contaminated fuel, unapproved silicone, oil and coolant.
  7. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With the engine running at normal operating temperature, monitor the DRBIII(R) parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
    • Review the DRBIII(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
    • Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

      Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.

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