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DTC P0420: 1/1 Catalytic Converter Efficiency: Testing

  1. Turn ignition on. Using scan tool, read DTCs. If GLOBAL GOOD TRIP counter is displayed and displayed count is "0", go to step  4. If GLOBAL GOOD TRIP counter is not displayed or displayed count is not "0", go to next step.
  2. At this time, conditions for catalyst efficiency failure do not exist or is an intermittent problem. Using scan tool, read and record FREEZE FRAME data. Road test vehicle under conditions in FREEZE FRAME data, paying particular attention to fault setting conditions such as speed, temperature, load and MAP vacuum. Using scan tool, read DTCs. If DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY returns, go to next step. If DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY does not return, no problem is indicated at this time. Test is complete.
  3. Check exhaust system for excessive smoke caused by internal oil or coolant consumption. Repair engine mechanical condition as necessary and replace catalytic converter. If engine mechanical condition is okay, go to next step.
  4. Start engine and allow it to idle. Check for exhaust leaks in right exhaust pipe between engine and downstream HO2S, behind 1/1 catalytic converter. Repair exhaust system as necessary. If exhaust system is okay, go to next step.
    5. NOTE: A new downstream HO2S used with an aging upstream HO2S may cause DTC P0420 to set.
  5. Review repair history. If downstream HO2S has been replaced without replacing upstream HO2S, replace upstream HO2S. If downstream HO2S has not been replaced recently or downstream HO2S has been replaced along with upstream HO2S, replace catalytic converter.
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