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Home >> Buick >> 2009 >> Allure CX >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 3.8L - DTC P0385 To DTC P2119 >> DTC P0420 >> Circuit/System Verification
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Circuit/System Verification

  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 when 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, perform steps 2-6 until the Test Result parameter indicates a Pass or a Fail.