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DTC P0421/P0422 - CATALYST EFFICIENCY BELOW THRESHOLD Hyundai Accent I

Testing & Diagnostics ~101 words
  1. P0421 - California models.
  2. P0422 - Federal models.
  1. Install scan tool. Start engine and check if DTC P0421 or P0422 is present. If DTC is present, go to next step. If DTC is not present, problem is intermittent.
  2. Check for exhaust leak before and after the catalytic converter. Repair as necessary. If leaks are not found, check rear O2S. For diagnosis, see related DTC or «SYSTEM/COMPONENT TESTS»(ref-16577) article. Replace as necessary. If O2S is okay, go to next step.
  3. Replace catalytic converter. Clear DTC. See CLEARING DTC(S). Retest system. If DTC resets, replace ECM.

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