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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 145 (Engine Control System & Fuel - 4.8L, 5.3L, 6.0L And 6.2L - DTC P0335 To DTC P3449) >> DTC P0420 or P0430 >> Circuit/System Verification

Circuit/System Verification

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NOTE: Refer to Three-Way Catalytic Converter Damage Notice .
NOTE: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice .
IMPORTANT: A new converter with less than 100 miles on it may set DTC P0420 or P0430 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
  1. If any other DTCs are set perform those diagnostics first.
  2. Inspect for the following conditions, which may cause a catalytic converter to degrade:
    • An engine misfire
    • High engine oil or high coolant consumption
    • Retarded spark timing
    • A weak or poor spark
    • A lean fuel mixture
    • A rich fuel mixture
    • A damaged oxygen sensor or wiring harness
    • The catalyst test may abort if the vehicle falls outside the conditions for running the DTC.
    • A catalyst may be temporarily degraded if a fuel with high sulfur content has been used. Drive the vehicle at highway speeds for 10 minutes and retest the converter.
  3. Operate the vehicle within the Conditions for Running the DTC.
    • If the DTC fails this key cycle, continue with this procedure.
  4. 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.
  5. Inspect the exhaust system for the following conditions:
    • Leaks
    • Physical damage
    • Loose or missing hardware
    • Properly torqued HO2S
    • Restrictions
    • If a condition is found, repair the exhaust system.
  6. Inspect the post catalyst HO2S for the following conditions:
    • A grounded wiring harness
    • Damage
    • If a condition is found, replace the post catalyst HO2S.
    • If no physical condition is detected, replace the catalytic converter.
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