P0403, P0404, P0405, P0406, P042E

WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.

The Ignition 1 Signal parameter is between 9-18 volts.
The engine is cranking or running.
The DTC P0401 intrusive test is not active.
These DTCs run continuously once the above conditions are met.