Skip the auto shop - Our mechanics make house calls

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

check engine light

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

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...

Related questions

Q: Getting error codes P0599 and P0171. Ive cleaned the O2 sensors but have no idea where to go from here.

Hello. Code P0599 is the code for an issue with the thermostat heater control circuit, while P0171 is for a lean condition on bank 1. P0599 is set when the computer detects that there is an issue with the electronically...

Q: How can I tell if it's my timing chain or something else?

Hi, thanks for writing in. Unfortunately, I will need a bit more information before confirming if the issue lies in your timing chain or not. Your car can certainly run and start with a timing issue, however it is not...

Q: The transmission will not shift out of 1st gear. The engine code reads TCM malfuction & P2714 Control solenoid stuck

Chevrolet released a Technical Service Bulletin about this issue in 2013. TSB Number:PI-1131. It suggests code P2714 may be caused by a stuck or non-functioning pressure control solenoid. If you've eliminated that as the cause and replaced the TCM, then...