Circuit Description
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.
VCM tests exhaust gas recirculation valve by momentarily commanding valve on while monitoring manifold absolute pressure. If expected manifold absolute pressure increase is not seen under certain operating conditions (decel) for a calibrated number of tests, VCM will turn on Malfunction Indicator Light (MIL) and store DTC P0401.