Action Taken When the DTC Sets

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

DTCs P2120, P2122, P2123, P2125, P2127, P2128, and P2138 are Type A DTCs.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.