Circuit/System Description
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2013 GMC Yukon XL, 2013 GMC Yukon, 2013 Chevrolet Suburban, 2013 Chevrolet Avalanche, and 2013 Cadillac Escalade EXT. However, it is still accessible from the selected car via links, so may be relevant.
The fuel tank pressure (FTP) sensor measures air pressure or vacuum in the evaporative emission (EVAP) system. The engine control module (ECM) supplies a 5 V reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system pressure or vacuum. The ECM also uses this FTP signal to determine atmospheric pressure for use in the engine-off small leak test, DTC P0442. Before using this signal as an atmospheric reference it must first be re-zeroed.