P0451 means the engine control module found the fuel tank pressure (FTP) sensor signal implausible: present, but not behaving as pressure should. Its neighbors are P0450 (circuit), P0452 (low), P0453 (high) and P0454 (intermittent). Range or performance is the code for a reading stuck at one value, a reading that does not respond when the EVAP system is sealed and pulled into vacuum, or a reading that disagrees with what other data say the pressure must be.
Severity: low. Can you keep driving? Yes. The sensor is part of the evaporative emissions monitor. The engine runs normally. The consequences are a check engine light, a failed emissions test, and often a second symptom that turns out to be the real story: a fuel nozzle that keeps clicking off when filling.
Why the sensor reads wrong when it is not broken
Volkswagen's specification for the Jetta Hybrid defines the monitor: P0451 sets when the difference between maximum and minimum EVAP system pressure is less than 0.05 kPa over 300 seconds. A sensor that sees no pressure change during a period when the system should be breathing is judged implausible. Anything that keeps the pressure flat at the sensor fails that test, and the bulletins show what does:
- Liquid fuel in the vapor line. GM bulletin 22-NA-203 (April 2024) for the 2021 to 2024 Buick Envision and 2019 Cadillac XT4: a customer who keeps filling past three clicks pushes liquid fuel into the vapor recirculation line, the liquid blocks the line, and the tank pressure sensor reads wrong. The correction is to disconnect the vapor lines at the tank, drain the liquid, clear the code and explain the three-click rule.
- A blocked air drain. Kia bulletin FUE 038 (revised June 2019) for the 2014 to 2018 Soul, 2012 to 2017 Rio and 2014 to 2017 Forte: early shut-off at the pump and P0451 or P0449, fixed by replacing the air drain case on the canister. Kia says explicitly not to replace the canister close valve for these codes.
- Water and ice in the canister. Audi bulletin 2044667/1 (June 2016) for the 2013 to 2015 RS 5: the nozzle keeps clicking off, P0451 is stored, and water or ice is found in the carbon canister reservoir and the leak detection pressure switch.
The pattern is a vent path that cannot breathe, and a sensor reporting the result honestly.
Causes, in the order they are found
A vent or vapor line blocked by liquid fuel, water, ice or debris · a canister saturated or its air drain blocked · a vent valve stuck closed · the sensor itself, stuck or drifted · a connector or wire problem on the sensor's three-wire circuit · a fuel cap that does not vent when it should · the module, last.
A diagnostic order
- Ask about fueling. Nozzle clicking off early, or a habit of topping off, points at the lines and canister before anything else.
- Watch tank pressure live with the cap off (should read near zero), the cap on, and with the system commanded sealed and purged. A value that never moves is the fault.
- Check the sensor's circuit: about 5 V reference, good ground, and a signal that changes when gentle pressure or vacuum is applied at the tank (a hand pump on the vent line, within the manufacturer's limits).
- Inspect and clear the vent lines and canister: disconnect at the tank, drain liquid, look for water, check the air drain, shake the canister.
- Replace the sensor only if its signal does not respond to a known pressure change with a good circuit.
- Clear and run the EVAP monitor with the scan tool, then let the readiness monitors complete.
Frequently asked questions
Can I drive with a P0451 code?
Yes. The sensor belongs to the emissions monitor and the engine is unaffected. Expect a check engine light and, on inspection, a failed emissions test until it is fixed.
Why does the fuel nozzle keep clicking off with P0451?
Because the same blocked vent path that keeps the tank pressure sensor from seeing normal pressure changes also keeps the tank from venting while it fills. Kia, Audi and GM each traced this pairing to liquid fuel, water or a blocked air drain in the vapor system rather than to the sensor.
Is P0451 the fuel tank pressure sensor?
Sometimes, but the code means the reading was implausible, and a sensor that cannot see pressure change because the line is blocked reads implausibly too. Test whether the signal responds to a real pressure change before replacing the sensor.
How much does it cost to fix P0451?
Draining a vapor line costs labor only. An air drain case or a vent valve is an inexpensive part. A tank pressure sensor is inexpensive but on many vehicles sits on top of the tank, which adds labor.
Related codes
- P0450 / P0452 / P0453 / P0454: the rest of the tank pressure sensor family.
- P0441 / P0449: purge flow and vent valve circuit, stored alongside in the Audi and Kia cases.
- P0442 / P0455 / P0456: EVAP leak codes; see P0442.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.