Diagnostic Aids
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
Normal scan tool reading in closed-loop will show O2S voltage varying between 10-1065 millivolts.
To locate an intermittent problem, use scan tool to monitor HO2S1 voltage with engine at normal operating temperature. Bias voltage (399-499 millivolts) will appear on scan tool if Purple wire or Tan wire are open.