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Home >> Chevrolet >> 2006 >> Cobalt LTZ >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 14 (Engine Controls - 2.0L - DTC P0420 To DTC P1682) >> DTC P0420 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
NOTE: Refer to Three-Way Catalytic Converter Damage Notice .
NOTE: Refer to Heated Oxygen Sensor (HO2S) Resistance Learn Reset Notice .
IMPORTANT: A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
  1. Inspect the catalytic converter for the following conditions:
    • Dents
    • A severe discoloration caused by excessive temperatures
    • Road damage
    • An internal rattle caused by damaged catalyst substrate
    • Restrictions
      • If a condition is found, replace the catalytic converter.
  2. Inspect the exhaust system for the following conditions:
    • Leaks
    • Physical damage
    • Loose or missing hardware
    • Properly torqued HO2S
    • If a condition is found, repair the exhaust system.
  3. Inspect the HO2S 2 for the following conditions:
    • A grounded wiring harness
    • Damage
    • If a condition is found, replace the HO2S 2.
    • If no physical condition is detected, replace the catalytic converter.
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