Possible causes

– Faulty Evaporative Emission System (EVAP) Vapor Pressure Sensor
– Evaporative Emission System (EVAP) Vapor Pressure Sensor harness is open or shorted
– Evaporative Emission System (EVAP) Vapor Pressure Sensor circuit poor electrical connection
– Faulty Engine Control Module (ECM)

When is the code detected?

Vapor pressure sensor output extremely changes under conditions of (a) and (b): (2 trip detection logic) – Vehicle speed: 0 km/h (0mph), Engine speed: Idling and VSV for pressure switching valve is OFF
Vapor pressure sensor value opening pressure valve of charcoal canister

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0451 LEXUS Description

The Evaporative Emission System (EVAP) vapor pressure sensor, VSV for canister closed valve (CCV) and VSV for pressure switching valve are used to detect abnormalities in the evaporative emission control system. The Engine Control Module (ECM) decides whether there is an abnormality in the evaporative emission control system based on the vapor pressure sensor signal.

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LEXUS Technical Service Bulletins for P0451 code