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P0499 OBD-II Trouble Code: Evaporative Emission System Vent Valve Control Circuit High

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P0499 code definition

If an OBD-II scanner has detected the P0499 code, it indicates that the ECM, or engine control module, has detected abnormal amounts of pressure in the evaporative emissions system.

What the P0499 code means

The evaporative emissions system is designed in part to limit the fuel vapors from being released into the atmosphere. At certain times, the EVAP system will open the purge valve to draw in fresh air for the system. If the EVAP system has not commanded a purge condition, and detects a high voltage pressure that should not be present in this non-purge condition, it will assume there has been a malfunction in the evaporative emission system vent valve, or its control circuit, and will alert the PCM to store the P0499 code.

What causes the P0499 code?

The most likely cause of an abnormal pressure in the evaporative emissions system vent valve control circuit is an improperly installed fuel cap.

Other causes may include:

  • Faulty purge control solenoid or valve
  • Faulty EVAP canister vent valve
  • Clogged charcoal canister
  • Broken charcoal canister
  • Cracked or broken vacuum or fuel vapor hoses
  • Faulty pressure sensor
  • Blown fuses, which may indicate a more serious issue

What are the symptoms of the P0499 code?

In most cases, the only other symptom noticeable with the P0499 code will be the illumination of the Check Engine light. There are likely to be other emissions system codes stored in the PCM.

How does a mechanic diagnose the P0499 code?

After an OBD-II scanner detects the P0499 code, a technician should begin with a visual inspection of all the wiring, connectors, and other electrical components of the emissions system. Any damaged elements should be replaced, reconnected, or repaired. The mechanic should then retest the system after clearing the code from the PCM. If the code reappears, then the mechanic has diagnosed an issue with the EVAP emissions system, and can begin further repairs.

Common mistakes when diagnosing the P0499 code

When diagnosing the underlying cause of the P0499 code, a common misdiagnosis is to replace the EVAP emissions system components rather than checking for a vacuum leak or an improperly installed fuel cap. These parts are more likely to be faulty than a part that needs replacement in many cases.

How serious is the P0499 code?

The P0499 represents a mild issue that should not affect the vehicle’s operation. In some cases, the presence of an unaddressed P0499 code may cause a vehicle to fail an emissions test. If the next tune up appointment is right around the corner, this issue can wait to be addresses at that time.

What repairs can fix the P0499 code?

In order to fix the underlying issue causing the P0499 code, a mechanic has several options to explore. Those may include:

  • Properly installing the fuel cap.
  • Replacing a faulty purge control solenoid or valve.
  • Replacing a faulty EVAP canister vent valve.
  • Clearing a clogged charcoal canister.
  • Replacing a broken charcoal canister.
  • Repairing or replacing cracked or broken vacuum or fuel vapor hoses.
  • Replacing a faulty pressure sensor.
  • Replacing blown fuses. This repair may indicate that there is a larger issue that must be addressed and repaired.

After each of these repairs has been attempted, it is important to clear the code from the PCM and perform a system retest. If the code does not reappear, the most recently performed repair was the root cause of the issue. This process helps mechanics narrow down intermittent issues and repair them quicker in the future should the issue return.

Need help with a P0499 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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