Conditions For Setting the DTC: U2003
WARNING: This page is about a different car, the 2002 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
U2003 is set, in the BCM, when it detects that the SPI serial data "B" circuit, is greater than 4.5 v for greater than 5 seconds.