Diagnostic Aids
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. 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.