Probable Causes:
WARNING: This page is about a different car, the 1997 GMC Pickup and 1997 Chevrolet Pickup. However, it is still accessible from the selected car via links, so may be relevant.
DTC will set when the following conditions are present:
- EGR flow test will fail and DTC P0401 set if VCM does not detect a sufficient rise in manifold absolute pressure during listed conditions.