P0451EVAP System Pressure Sensor/Switch A Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. The tank pressure sensor measures small pressures around ambient for the leak tests. Its direction differs by maker – on GM vacuum raises the voltage, on Ford and Bosch pressure does – so low and high refer to the signal voltage only. P0451 is its plausibility check. GM checks during the engine-off leak test that the signal settles to ambient pressure with the vent open and averages several tests; Ford checks the offset after at least 4–6 hours off (±0.5 kPa). Saab's Bosch ME9 watches start pressure, the drop during purging and excessive oscillation. On Subaru a leaking or blocked hose between sensor and tank is a frequent cause.
- What you may notice
- Check engine light on
- EVAP readiness not set, emission inspection not passed
- No change in driving
- Likely causes
- LikelyTank pressure sensor offset shifted or sluggish
- PossibleVent line or canister blocked (pressure does not release)
- PossibleSensor hose or port leaking, kinked or blocked
- RareTank overfilled, fuel in the lines
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.