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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 149 (ENGINE CONTROL SYSTEM - 3.8L - DTC P0220 To DTC P0449) >> DTC P0403 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect the EGR valve harness connector and probe the EGR High Control circuit with a test lamp connected to ground. Command the EGR valve from 0 percent to 10 percent and back to 0 percent. The test lamp should illuminate when commanded to 10 percent.
    • If the test lamp remains illuminated when commanded to 0 percent, test the EGR High Control circuit for a short to voltage.
    • If the test lamp does not illuminate, test the EGR High Control circuit for an open, high resistance or short to ground.
  2. Connect a test lamp between the EGR High Control circuit and the EGR Low Control Circuit. Command the EGR valve from 0 percent to 10 percent and back to 0 percent. The test lamp should illuminate when commanded to 10 percent.
    • If the test lamp illuminates when commanded to 10 percent replace the EGR valve.
    • If the test lamp does not illuminate, test the EGR Low Control circuit for an open, high resistance.
    • If all circuits test OK, replace the control module.
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