DTC P0451: EVAP System Pressure Sensor - Range/Performance: Condition
WARNING: This page is about a different car, the 2002 Suzuki XL-7. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0451 is set when ECM detects fuel tank internal pressure is not close to atmospheric pressure (varied from the atmospheric pressure by the specified pressure value or more), and change in fuel tank internal pressure is less than the specified value. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles.