P0451: Evaporative emission system pressure sensor/switch range/performance

How to read it

P0451 is one of the standard OBD-II trouble codes stored when the check engine light comes on. SAE J2012, the standard that defines the codes, names it “Evaporative Emission System Pressure Sensor/Switch Range/Performance”; an Audi service bulletin gives the same name, writing the code with a two-digit suffix as P045100.

Also searched as: code P0451, P0451 code.

What the monitor checks

The federal rule requires the system to detect vapour leaks in the evaporative system and an absence of purge air flow from it.

Look-alikes

In SAE J2012 the next code, P0452: Evaporative emission system pressure sensor/switch low, is for the same pressure sensor or switch reading low. P0451 is for a reading out of range or not behaving as expected.

What the manual says to do

Ford’s F-150 manual says that if the indicator stays on, the vehicle should be serviced at the first available opportunity, and that continued driving with it on can mean higher emissions, lower fuel economy, rougher running and more costly repairs.

How the light goes out

Under the federal rule, the check engine light may go out once the fault has not come back during three trips in a row in which its monitor runs without finding it. The system may erase the stored code if the same code has not been registered again in at least 40 engine warm-up cycles.