Circuit/System Verification
WARNING: This page is about a different car, the 2008 Saturn Outlook, 2008 GMC Acadia, and 2008 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, transmission in REVERSE, verify that Sensor Feed Voltage Output scan tool parameter value is greater than 8.0 Volts.