P0451 Code: Evaporative Emission System Pressure Sensor/switch

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p0157 code displaying on an OBD-2 diagnostic tool

Table of Contents

P0157 code definition

Evaporative Emission System Pressure Sensor/switch.

What is the P0451 code?

The P0451 code is a diagnostic trouble code that indicates the pressure sensor/switch has failed. This is part of your evaporative emission system, which helps control the amount of fuel vapor in your exhaust. When this sensor/switch fails, it will cause your vehicle to run poorly and may even prevent it from starting.

The most common causes for this DTC are:

  • A bad PCM (powertrain control module) or ECM (electronic control module).

Common causes of the P0451 code

As the name suggests, P0451 indicates a problem with your vehicle’s evaporative emission system. To understand what causes this code to come up and what you can do to fix it, we’ll need to take a closer look at how it works.

The evaporative emission system consists of the following:

  • The fuel tank (which holds gas)
  • A vapor line that runs from the gas cap through the firewall into the engine compartment
  • A charcoal canister (which contains activated carbon) is located behind or under your rear seat in some cars; if yours doesn’t have one, then there will be just one line going from under your hood straight into another part inside called an EVAP canister housing assembly (this houses all related parts).

Symptoms of the P0451 code

If you have a P0451 code, there are several symptoms to look out for. Some of them include the following:

  • Check engine light comes on
  • Reduced power or loss of power while driving
  • Rough idle and misfires while idling or driving in traffic (may feel like your engine is stalling)

In addition to these symptoms, you may notice that your fuel consumption has increased as well.

How to diagnose the P0451 code?

To diagnose the P0451 code, you’ll need to use a scan tool. First, check for vacuum leaks by watching your engine revamping it up and holding your hand over each hose or connection. If you hear air hissing from one of them, that’s your problem. Next, check fuel pressure by running the engine at idle with the cap off of your fuel tank; if there’s no pressure build-up in five minutes or so (about 3 PSI), then it could be a faulty gauge or switch on its way out—but if there is pressure built up within those five minutes (around 30 PSI), look elsewhere for an issue since that means everything else is working fine.

Next up: Coolant levels should be checked with every oil change as part of routine maintenance anyway because coolant levels need to stay within spec throughout their lifespan, so pay attention here, folks.

Exhaust leaks can also cause this issue, so take care when inspecting anything related to exhaust piping. Oxygen sensors are another common culprit, so keep an eye out while checking these items off our list. Finally, check the fuel injector function using either an Oxygen Sensor Test Light tool or just putting some gas down each line until one starts blinking rapidly – both methods should do the trick, but only use one way per car model since some vehicles may require different approaches depending upon year/make/model type information stored within their ECU.

How serious is the P0451 code?

The P0451 code is not dangerous, but you should fix it. It’s not a severe problem, but it could cause other problems if not corrected.

Can I still drive?

If you have a P0451 code, you should only drive the vehicle once it has been diagnosed. It could be a bad sensor or switch, but it could be something else entirely. If you drive the car and damage your catalytic converter in the process, then that would cost more money than just getting it fixed right away.