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DTC P0420: 1/1 Catalytic Converter Efficiency: Testing

  1. Turn the ignition on. With the DRBIII®, 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 damaged Catalytic Converter, dents, holes and severe discoloration caused by overheating the Catalytic Converter. Also check if Catalytic Converter is broken internally or leaking. Were any problems found? If yes, replace the Catalytic Converter. Repair the condition that may have caused the failure. If no, go to next step.
  3. Inspect the exhaust for leak between the engine and the O2 sensor. Inspect the exhaust for leaks between the engine and the appropriate rear 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. A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the vehicles repair history. Has the rear O2 Sensor been replace without replacing the front O2 Sensor? If yes, replace the Front 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.
  7. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® 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® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (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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