P2088, P2090, P2092, P2094
WARNING: This page is about a different car, the 2009 Pontiac Torrent and 2009 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects a short to ground in the CMP actuator solenoid circuits for greater than 1 second or a cumulative of 5 seconds, when the solenoid is commanded OFF.