Faulty EVAP / fuel tank pressure sensor (OBD-Codes.com, RepairPal). Wiring or connector problems in the pressure sensor circuit, or less often an engine computer fault (OBD-Codes.com; RepairPal lists sensor, wiring or computer together). Loose or missing fuel cap (OBD-Codes.com). RepairPal lists the fuel cap as a common misdiagnosis for this code, so treat it as a quick check rather than the likely fix. Broken, collapsed or burned EVAP hoses or lines (OBD-Codes.com). Cracked or broken charcoal canister (OBD-Codes.com; RepairPal lists a defective carbon canister). Clogged fuel tank pressure relief valve (OBD-Codes.com). Defective fuel tank sending unit, or a defective or damaged fuel tank (RepairPal). Defective canister vent valve, in some cases (RepairPal; RepairPal also lists the purge and vent valves as common misdiagnoses).

Replace a fuel tank pressure sensor that fails the manufacturer's test (OBD-Codes.com, RepairPal). Repair open or shorted wiring in the sensor circuit (OBD-Codes.com; RepairPal says to verify the 5-volt reference, ground and signal circuits). Tighten or replace a faulty fuel cap, if it is actually the problem (OBD-Codes.com). Replace damaged EVAP hoses or lines, or a cracked charcoal canister (OBD-Codes.com). Repair a fuel tank, sending unit or vent valve problem found during diagnosis (RepairPal). Engine computer diagnosis or replacement only after all sensor and wiring tests pass (RepairPal).

P0451🌫 Emissions / evaporative emission (EVAP) systemDrive with caution, fix soon

P0451: EVAP System Pressure Sensor Range/Performance (Meaning, Causes, Fixes)

Q: What does P0451 mean?

P0451 means the engine computer is getting a reading from the EVAP (fuel tank) pressure sensor that is out of its expected range or doesn't make sense. Common causes listed by the sources are a faulty fuel tank pressure sensor or its wiring, a loose or missing fuel cap, damaged EVAP hoses or canister, and less often a fuel tank or computer problem. The evaporative emission (EVAP) system catches fuel vapor from the fuel tank, stores it in a charcoal canister, and later draws it into the engine to be burned. The EVAP pressure sensor, also called the fuel tank pressure sensor, tells the engine computer how much pressure or vacuum is in the fuel tank and EVAP system, and it is the main sensor the computer relies on for its leak tests. OBD-Codes.com describes P0451 as a generic OBD-II code that sets when the computer detects a malfunction in the EVAP pressure sensor circuit, or when EVAP or fuel tank pressure is not within a preset range over a set period under certain conditions. RepairPal defines it as the pressure sensor reporting pressure changes that are out of specification during the EVAP monitor test or normal driving, and says shops see it set when the readings are irrational or out of range for ten seconds after a cold start, on two successive cold starts. The sensor usually sits on top of the fuel tank, on or near the fuel pump and fuel level sending unit, which can make it hard to reach. The sources differ on whether a loose fuel cap is a likely cause (OBD-Codes.com lists it, RepairPal calls it a common misdiagnosis), so check your vehicle's service information. Related codes include P0450 (pressure sensor circuit), P0452 (sensor low), P0453 (sensor high) and P0454 (sensor intermittent).

Q: Can I keep driving with P0451?

Drive with caution, fix soon. Get it diagnosed within a reasonable time. RepairPal rates P0451 Moderate, meaning it may not threaten safety or drivability right away but should still be checked. Both OBD-Codes.com and RepairPal say that in most cases you will notice nothing besides the check engine light. It can keep the car from passing an emissions inspection. If you smell raw fuel, get it checked sooner, and never ignore a strong fuel smell.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0451 means

The evaporative emission (EVAP) system catches fuel vapor from the fuel tank, stores it in a charcoal canister, and later draws it into the engine to be burned. The EVAP pressure sensor, also called the fuel tank pressure sensor, tells the engine computer how much pressure or vacuum is in the fuel tank and EVAP system, and it is the main sensor the computer relies on for its leak tests. OBD-Codes.com describes P0451 as a generic OBD-II code that sets when the computer detects a malfunction in the EVAP pressure sensor circuit, or when EVAP or fuel tank pressure is not within a preset range over a set period under certain conditions. RepairPal defines it as the pressure sensor reporting pressure changes that are out of specification during the EVAP monitor test or normal driving, and says shops see it set when the readings are irrational or out of range for ten seconds after a cold start, on two successive cold starts. The sensor usually sits on top of the fuel tank, on or near the fuel pump and fuel level sending unit, which can make it hard to reach. The sources differ on whether a loose fuel cap is a likely cause (OBD-Codes.com lists it, RepairPal calls it a common misdiagnosis), so check your vehicle's service information. Related codes include P0450 (pressure sensor circuit), P0452 (sensor low), P0453 (sensor high) and P0454 (sensor intermittent).

Severity: can I keep driving?

Drive with caution, fix soon

Get it diagnosed within a reasonable time. RepairPal rates P0451 Moderate, meaning it may not threaten safety or drivability right away but should still be checked. Both OBD-Codes.com and RepairPal say that in most cases you will notice nothing besides the check engine light. It can keep the car from passing an emissions inspection. If you smell raw fuel, get it checked sooner, and never ignore a strong fuel smell.

Common symptoms

Check engine (service engine soon) light on (OBD-Codes.com, RepairPal)
In most cases no other symptoms; both sources say the driver usually won't notice anything else
A slight decrease in fuel efficiency (OBD-Codes.com)
Possible fuel odor from escaping fuel vapor in some cases (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Faulty EVAP / fuel tank pressure sensor (OBD-Codes.com, RepairPal)
Wiring or connector problems in the pressure sensor circuit, or less often an engine computer fault (OBD-Codes.com; RepairPal lists sensor, wiring or computer together)
Loose or missing fuel cap (OBD-Codes.com). RepairPal lists the fuel cap as a common misdiagnosis for this code, so treat it as a quick check rather than the likely fix
Broken, collapsed or burned EVAP hoses or lines (OBD-Codes.com)
Cracked or broken charcoal canister (OBD-Codes.com; RepairPal lists a defective carbon canister)
Clogged fuel tank pressure relief valve (OBD-Codes.com)
Defective fuel tank sending unit, or a defective or damaged fuel tank (RepairPal)
Defective canister vent valve, in some cases (RepairPal; RepairPal also lists the purge and vent valves as common misdiagnoses)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes and write down the freeze frame data. Other EVAP codes (such as P0446 or P0455) can point to a related problem.
Remove the fuel cap, check its seal, and screw it back on properly until it clicks (OBD-Codes.com). RepairPal warns the cap is often not the real cause, so don't stop here if the code returns.
Look over the EVAP hoses, lines and wiring you can reach, especially near sharp edges or hot exhaust parts, for cracks, collapse, burns or chafing (OBD-Codes.com).
Clear the code and drive normally. OBD-Codes.com notes EVAP codes almost always need several drive cycles before the system retests, so the light may take a while to come back or stay off.

Typical fixes

Replace a fuel tank pressure sensor that fails the manufacturer's test (OBD-Codes.com, RepairPal)
Repair open or shorted wiring in the sensor circuit (OBD-Codes.com; RepairPal says to verify the 5-volt reference, ground and signal circuits)
Tighten or replace a faulty fuel cap, if it is actually the problem (OBD-Codes.com)
Replace damaged EVAP hoses or lines, or a cracked charcoal canister (OBD-Codes.com)
Repair a fuel tank, sending unit or vent valve problem found during diagnosis (RepairPal)
Engine computer diagnosis or replacement only after all sensor and wiring tests pass (RepairPal)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The sensor is usually on top of the fuel tank, and reaching it may mean lowering the tank or removing access panels (OBD-Codes.com)
Testing needs a scan tool to watch the tank pressure reading live, a multimeter, and a vacuum gauge or smoke machine (OBD-Codes.com, RepairPal)
The code comes back after the fuel cap has been checked
You smell raw fuel, have trouble filling the tank, or the fuel tank or filler neck looks damaged

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0451 serious?

RepairPal rates it Moderate. Both OBD-Codes.com and RepairPal say most cars show no symptoms besides the check engine light, though OBD-Codes.com mentions slightly lower fuel economy and RepairPal mentions a possible fuel smell. It usually isn't an emergency, but it can fail an emissions inspection, so get it diagnosed within a reasonable time.

Can a loose gas cap cause P0451?

The sources disagree. OBD-Codes.com lists a loose or missing fuel cap as a possible cause and suggests checking it first. RepairPal lists the fuel cap as a common misdiagnosis for P0451. Checking the cap is quick and free, but if the code comes back, the pressure sensor and its wiring are the next things to test.

Where is the EVAP pressure sensor?

Usually on top of the fuel tank, often on or built into the fuel pump and fuel level sending unit (OBD-Codes.com, RepairPal). That's why it can be hard to reach.

How much does it cost to fix P0451?

Neither source gives a repair cost. It can range from a fuel cap or hose to a new tank pressure sensor that requires fuel tank access, so get a diagnosis and a written estimate first.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.