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Home >> Hummer >> 2009 >> H3 Alpha >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 5.3L - DTC P0315 To DTC P064A >> DTC P0420 or P0430 >> Circuit/System Verification
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Circuit/System Verification

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. Verify that no other DTCs are set.
  2. Operate the vehicle within the Conditions for Running the DTC while observing the scan tool TWC Mon. OFF Idle Test Conditions Met parameter. The parameter will change to Yes when the OFF Idle Conditions have been met.
    • If not the specified value, operate the vehicle within the OFF Idle Conditions.
  3. When the parameter has changed to Yes and the conditions are safe, stop and idle the vehicle in gear.
  4. Apply the service brake.
  5. Monitor the scan tool TWC Monitor Test State parameter. When the parameter indicates Active, the TWC Mon Test is running.
  6. Continue to monitor the parameter. When the parameter indicates Inactive, the TWC Mon Test has completed.
  7. When the test has completed, the TWC Monitor Test Count parameter will increment by one and the TWC Monitor Test Result parameter will indicate Pass, Fail, or No Decision.
    • If no decision has been made, repeat steps 2-6 until the Test Result parameter indicates a Pass or Fail.
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