DTC will set when the following conditions are present:

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1997 GMC Yukon, 1997 GMC Suburban, 1997 GMC Pickup, 1997 GMC Cab & Chassis, and 1997 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

EGR flow test will fail and DTC P0401 set if VCM does not detect a sufficient rise in manifold absolute pressure during listed conditions.