P0451 code meaning
EVAP System Pressure Sensor/Switch A Circuit Range/Performance
Powertrain system Generic code P04xx codes Check engine light
What P0451 means
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.
P0451 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0451
- Check engine light on
- EVAP readiness not set, emission inspection not passed
- No change in driving
Common causes of P0451
- Most likelyTank pressure sensor offset shifted or sluggish
- PossibleVent line or canister blocked (pressure does not release)
- PossibleSensor hose or port leaking, kinked or blocked
- Less likelyTank overfilled, fuel in the lines
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel tank pressure sensorSensor wiringEngine control module
What each part of P0451 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 51 | The exact fault in that area. |
What to do next
- Note P0451 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0451
What does P0451 mean?
P0451 means "EVAP System Pressure Sensor/Switch A Circuit Range/Performance". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0451?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0451 fail an emissions test?
Yes, it can. P0451 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0451 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0451 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.