P0451 DTC Code: EVAP Pressure Sensor Range/Performance

Quick answer

• What the code means: The P0451 code means the evaporative emission control (EVAP) system's pressure sensor is reporting a value that is out of its normal operating range.
• Severity: Safe to keep driving. This code will not leave you stranded, but it will cause you to fail an emissions test.
• Most common cause: A faulty or failing EVAP pressure sensor.

What the P0451 code means

The official OBD-II definition for P0451 is "Evaporative Emission Control System Pressure Sensor/Switch Range/Performance." In plain English, this means that your car's computer (the powertrain control module, or PCM) has detected that the voltage signal from the EVAP pressure sensor is not what it should be. The EVAP system is responsible for trapping and purging fuel vapors from the fuel tank so they don't escape into the atmosphere. The pressure sensor measures the pressure and vacuum in the system to ensure it's working correctly. When the sensor's readings are irrational or out of specification, it triggers the P0451 code.

Common symptoms

Unlike many other trouble codes, a P0451 will rarely cause any noticeable drivability issues. The most common symptoms are:

• Check Engine Light is on
• A slight decrease in fuel economy
• A faint smell of fuel

Common causes

The causes of a P0451 code, in order from most to least likely, are:

1. Faulty EVAP pressure sensor: This is the most common cause. The sensor itself can fail, or the wiring to it can become damaged.
2. Loose or faulty gas cap: A gas cap that is not tightened properly, or one that has a bad seal, can cause a small leak that the pressure sensor will detect.
3. Leaks in the EVAP system: The hoses and lines that make up the EVAP system can crack, split, or become disconnected over time, causing a leak.
4. Faulty purge or vent solenoid: These solenoids control the flow of fuel vapors in the EVAP system. If they are not working correctly, they can cause pressure problems.
5. Faulty charcoal canister: The charcoal canister stores fuel vapors. If it becomes saturated with fuel or damaged, it can cause the P0451 code to set.

How a technician diagnoses it

A technician will follow these steps to diagnose a P0451 code:

1. Scan for codes: The technician will first use a scan tool to confirm that the P0451 code is present and to check for any other related codes.
2. Inspect the gas cap: The technician will make sure the gas cap is tight and that the seal is in good condition.
3. Inspect the EVAP system: The technician will visually inspect all of the EVAP hoses, lines, and components for any signs of damage or leaks.
4. Test the EVAP pressure sensor: The technician will use a scan tool to monitor the voltage from the EVAP pressure sensor. A good sensor should show a voltage that changes as the pressure in the system changes. A bad sensor will show a voltage that is stuck at one value, or that is erratic.
5. Perform a smoke test: If no visible leaks are found, the technician will perform a smoke test. This involves injecting smoke into the EVAP system and looking for where it escapes. This is the most effective way to find very small leaks.

Typical repair cost

The cost to repair a P0451 code can vary widely depending on the cause. Here are some typical repair costs:

• Gas cap: $15 – $60
• EVAP pressure sensor: $150 – $350
• EVAP hose: $50 – $200
• Charcoal canister: $400 – $800
• Smoke test/diagnosis: $100 – $200

The total cost will depend on the make and model of your vehicle, as well as the labor rates in your area.

Can I keep driving with this code?

Yes, it is generally safe to keep driving with a P0451 code. The code will not cause any damage to your engine, and it will not affect the drivability of your vehicle. However, you will not be able to pass an emissions test until the problem is fixed. It is also possible that a small fuel leak could be a fire hazard, so it is best to have the problem diagnosed and repaired as soon as possible.

Related codes

• P0440: Evaporative Emission Control System Malfunction
• P0441: Evaporative Emission Control System Incorrect Purge Flow
• P0442: Evaporative Emission Control System Leak Detected (small leak)
• P0455: Evaporative Emission Control System Leak Detected (gross leak)
• P0456: Evaporative Emission Control System Leak Detected (very small leak)

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