Possible causes

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

Tech notes

There is a factory service bulletin for the following Mercury models:

2005-2008 Mercury Mariner
Mercury Factory Service Bulletin OBDII Code P0451

When is the code detected?

An improper voltage signal from EVAP control system pressure sensor is sent to Engine Control Module (ECM).

Symptoms

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

P0451 MERCURY Description

The Evaporative Emission System (EVAP) control system pressure sensor detects pressure in the purge line. The sensor output voltage to the Engine Control Module (ECM) increases as pressure increases. The EVAP control system pressure sensor is not used to control the engine system. It is used only for on board diagnosis.

MERCURY Technical Service Bulletins for P0451 code