P0450

P0450 is the generic EVAP pressure sensor (also called fuel tank pressure sensor or FTPS) malfunction code - the ECM detected a sensor reading that's electrically valid but doesn't behave plausibly during normal operation or leak-test cycles. The FTPS is a piezo-resistive transducer that monitors EVAP system pressure or vacuum, and on most modern vehicles outputs a 0.5 to 4.5V signal corresponding to roughly atmospheric (about 2.5V at sea level) down to negative 7 to 10 inches of water column during purge events. Cheapest-first ladder: scan-tool the live FTPS data with the engine off and the gas cap removed - the sensor should read very close to atmospheric (typically 2.4 to 2.6V or the OEM 'zero' equivalent). With the gas cap installed and the engine running and warm, command an EVAP purge via bidirectional control and watch the FTPS go slightly negative as the purge valve draws vacuum on the tank. If the sensor flatlines, jumps erratically, or fails to respond to commanded purge, it has failed. Backprobe the connector and verify 5V reference (4.9 to 5.1V), clean ground (under 0.1V drop), and a smooth signal voltage that tracks system pressure changes. The expensive misdiagnosis is replacing the entire fuel pump module assembly when the FTPS is the only failed component - on many platforms (especially GM trucks) the sensor is a separately-serviceable part that mounts on top of the fuel pump module or on a dedicated saddle-tank port, so verify part availability before quoting a $400 to $800 pump module.

Vehicle-specific patterns: 1999-2013 GM full-size pickups with saddle-tank fuel systems (Silverado, Sierra, Suburban, Tahoe 1500-3500) are the classic P0450 platform - the FTPS mounts on the cross-over line between the two saddle tanks and gets fuel-soaked from a leaking quick-connect, killing the sensor. The aftermarket sells the standalone FTPS for $40 to $90 even though the dealer wants to sell the full crossover assembly. 2005-2014 Subaru EJ-series (Outback, Forester, Legacy) FTPS mounts on top of the fuel pump module under the rear seat and fails from heat aging plus fuel vapor exposure - typically presents around 120k to 150k miles. 2007-2014 Toyota Tundra/Sequoia 5.7L FTPS fails from connector corrosion when the pump module gasket weeps fuel. 2009-2014 Ford F-150 FTPS gets damaged when the EVAP canister is replaced and the sensor connector pin gets bent during reinstallation. Estimated repair: $70 to $350.