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P0459 OBD-II Trouble Code: Evaporative Emissions System Purge Control Valve Circuit High

Check Engine Light

P0459 code definition

The P0459 code means that there has been a problem experienced with the vehicle’s evaporative (EVAP) system.

What the P0459 code means

If the P0459 code is set in the car’s computer, it means there has been a problem experienced within the evaporative system. This system includes a wide range of components, including the gas cap, the fuel filter, the system pressure sensor, flow sensor and many more. The car’s computer monitors fuel system pressure through a voltage reading. When that voltage is higher than expected, the system may turn on the Check Engine light.

What causes the P0459 code?

Potential causes for the P0459 code are varied, but they include the following:

  • Loose gas cap
  • Failed or damaged gasket on the gas cap
  • Damaged charcoal canister
  • Failed purge control solenoid
  • Damaged vacuum hoses
  • Damaged fuel vapor hoses
  • Faulty pressure sensor
  • Faulty flow sensor
  • Faulty PCM (rare)

What are the symptoms of the P0459 code?

The only symptom of a P0459 code is the Check Engine light turning on in the dash. This code should not result in drivability problems.

How does a mechanic diagnose the P0459 code?

The first step to diagnosing the P0459 code is connecting an OBD II scanner to the car’s computer and reading the codes stored there. It is likely there are several other evaporative system codes present. Next, the car should be test driven to see if the codes reset.

Following the test drive, the mechanic should begin with a visual and physical examination of the gas cap’s condition, including whether it is correctly installed and the condition of the gasket. If the problem is not related to the gas cap, the mechanic should inspect all vacuum lines for cracking or damage. The purge control solenoid should be tested (note that this may require the use of a vehicle lift and a smoke machine). A mechanic may also need to inspect all other evaporative system components, including the charcoal canister, fuel vapor hoses, pressure sensor, flow sensor and more. Note that solenoids should be removed from the vehicle before being tested.

Common mistakes when diagnosing the P0459 code

One of the most common mistakes seen when diagnosing the P0459 code is replacing parts without first performing a full diagnostic on the vacuum system. Loss of vacuum is the primary cause for the P0459 code to be set in the computer, and should be ruled out before any parts are replaced.

How serious is the P0459 code?

While the P0459 code will not result in drivability problems with your vehicle, it can lead to combustible fuel vapors being released into the atmosphere. This will also result in the car not being able to pass emissions testing. In a worst-case scenario, it can also have an adverse effect on fuel economy as the engine may not be able to burn fuel vapor correctly.

What repairs can fix the P0459 code?

The most common repair for the P0459 code is to inspect the fuel cap and reinstall it. Gas cap replacement is also common. However, in older vehicles, as well as those driven in areas where adverse conditions are common, vacuum line deterioration can be common. Other repairs include replacing damaged or failed solenoids, replacing the charcoal canister or a faulty sensor.

Additional comments for consideration regarding the P0459 code

While an incorrectly installed gas cap is one of the primary causes of the P0459 code, the vehicle should be thoroughly inspected to rule out any other potential causes, such as damaged vacuum or fuel vapor lines.

Need help with a P0459 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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