P0451 OBD-II Trouble Code: Evaporative Emission Control System Pressure Sensor Range/Performance

Diagnostic Trouble Code (DTC): P0451

P0451 code definition

When the PCM (powertrain control module) detects an incorrect, erratic, or otherwise improper voltage signal from the evaporative emission control system pressure sensor, a P0451 code is set and the Check Engine Light illuminates.

What the P0451 code means

As fuel is stored in the vehicle’s fuel storage system, some of it will evaporate over time. As this happens, the evaporative emission control system captures that evaporated fuel and then systematically purges it into the engine’s combustion process. When the P0451 code is set, it shows that the evaporative pressure sensor has detected pressure changes that are outside the accepted manufacturer specifications for the vehicle.

What causes the P0451 code?

A few different problems may cause the P0451 code to be stored. These include:

• A defect in, or damage to, the gas tank
• A problem with the fuel tank sending unit
• A faulty fuel tank pressure sensor
• An open or shorted fuel tank pressure sensor circuit
• A faulty canister vent valve (somewhat rare)
• A faulty PCM (rare)

What are the symptoms of the P0451 code?

In almost all cases, the only symptom will be the illumination of the Check Engine Light. In some cases, however, you may notice the smell of gasoline coming from your vehicle’s engine. In most instances, other codes related to the evaporative emission control system will begin to appear as well.

How does a mechanic diagnose the P0451 code?

Using an OBD-II scanner, the mechanic will identify the codes that have been saved by the PCM. They’ll then begin addressing each code in the order in which it was stored. In most cases, when a P0451 code is stored, other related codes will be stored after it, so the P0451 code should be resolved first.

The first thing to look for in this case, after identifying the code(s), will be damaged, corroded, chafed, or otherwise faulty wiring, connectors, and circuits. After repairing any instances of these, the mechanic will clear the code(s) and retest the system. Then they will move on inspect the charcoal canister, the purge valve, the vacuum and vapor hoses, and all other components related to the evaporative emission control system. With each inspection and repair, they will clear the codes and retest the engine until the problem is resolved.

Common mistakes when diagnosing the P0451 code

The most common mistake associated with a P0451 code is failing to properly inspect all components, wiring, and connectors before replacing any part of the evaporative emission control system. For example, in some cases, a vacuum leak could be due to a loose or damaged fuel cap, not a faulty vacuum hose.

What repairs can fix the P0451 code?

In some instances, the repair for a P0451 code could be as simple as replacing the gas cap. Most of the time, though, resolving the issue will involve one or more of the following repairs:

• Repairing or replacing the gas tank.
• Repairing or replacing a faulty fuel tank pressure sensor.
• Replacing defective or damaged wiring or connectors in the fuel tank pressure sensor circuit.
• Replacing the canister vent valve.
• Replacing or reprogramming the PCM (rare).

Additional comments for consideration regarding the P0451 code

Because it usually has no discernible symptoms, other than the Check Engine Light illuminating, some vehicle owners assume that a P0451 code is not a serious issue and that it doesn’t need to be resolved until the vehicle is due for an OBD-II emissions test. However, this issue can result in significantly lower fuel efficiency, and it can trigger other problems, as well. Thus, it’s important to resolve it before it costs you more time and money later on.

Furthermore, if a more extensive repair is needed to resolve the code, it’s a good idea to address these sooner rather than later, especially when you need to resolve the code in order to pass an emissions test and renew your vehicle’s registration.

Need help with a P0451 code?

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