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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1376 (Engine Controls And Fuel - Hybrid (Hp2) 6.0L (LFA) - DTC P0231 To DTC P069E) >> DTC P0420 or P0430 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: Refer to Three-Way Catalytic Converter Damage Caution .
CAUTION: Refer to Heated Oxygen Sensor Resistance Learn Reset Caution .
NOTE: 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. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description .
  2. Ignition ON, verify the scan tool Hood Position parameter displays Open.
  3. 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.
  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.
  7. If all physical conditions test normal, test or replace the catalytic converter.
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