P0499 – Evaporative emission control system vent valve control circuit high

 

EVAP system vent control circuit high 

 

 

The P0499 code means your engine control unit (ECU) or powertrain control module (PCM) has detected an issue with the evaporative emission control (EVAP) system – the system that keeps fuel vapors from escaping into the air. 

 

Specifically, this generic powertrain code signals that the vent control circuit reads unusually high pressure, often due to issues like a faulty vent valve. 

 

The EVAP system works by capturing fuel vapors from the fuel tank in a charcoal canister. These vapors are then purged into the engine for combustion when needed. Key components include the vent valve, which allows fresh air into the system; the purge valve, which controls the flow of vapors to the engine; and sensors that monitor fuel tank pressure to ensure everything is functioning properly. 

 

The figure below shows how these components interact to manage fuel vapors and maintain the system’s efficiency:  

 

 

The ECU runs regular self-checks to ensure the EVAP system is working correctly. If it detects that the vent valve isn’t working properly or the system has excessive pressure, it flags the P0499 code. This code often appears alongside other EVAP-related codes, giving more clues about what’s wrong. 

 

 

 

Trouble code P0499 won’t damage your vehicle or affect its performance. However, you could run into other headaches, like failing emission inspections.  

 

Thankfully, in most cases, this isn’t a costly repair. 

 

 

Yes, your car will still run fine with this code, and it won’t harm your engine or affect how it drives. 

 

However, there are some drawbacks. It can lead to a failed emissions test and trigger the check engine light. If you ignore it, that persistent check engine light might hide more serious problems later. 

 

 

The most obvious clue is the check engine light. Beyond that, there are usually no other noticeable symptoms. 

 

 

Most often, P0499 appears due to:  

 

Use these tips to diagnose and fix a P0499 code accurately:  

 

 

Check for other related trouble codes using an OBD code reader. These codes may provide additional clues to the underlying problem:  

 

 

 

First, use your scan tool to clear the P0499 fault code from your car.  

After the test drive, perform another scan to see if the code reappears. If it does, this confirms the problem persists and requires further investigation.   

 

 

Even though this isn't the primary cause of the P0499 code, it's still quite common and worth inspecting since it only takes only a few seconds. Make sure the gas cap is tight and undamaged.  

 

Check the condition of the rubber O-ring and replace it if necessary. If you notice any dirt or debris on the gas cap or seal, clean it using WD-40.  

 

 

Check the EVAP system for leaks. A smoke test is an effective way to locate leaks by filling the system with smoke. The smoke visibly escapes from cracks, holes, or loose connections, so it's easier to identify the issue's exact location. 

 

 

If you don’t find any leaks, focus on the vent valve. Ensure the vent solenoid moves freely and isn't stuck, and clear any debris blocking it. Also, look for a blocked EVAP vent path, pinched vent hose, or damaged EVAP vent housing. 

 

Finally, closely check the electrical circuit – there might be signs of damage or loose connections in the wiring. 

 

 

 

The EVAP vent valve solenoid usually sits near the fuel tank. It's often attached to the charcoal canister, which is a large black box. Look for the EVAP canister under the car or, in some models, behind the rear wheel well. Refer to your vehicle’s service manual for the exact location. 

 

 

The cost of an EVAP vent valve typically ranges from $20 to a few hundred dollars, depending on the vehicle. The labor cost can add another $50 or more, based on the shop and location. The total cost will vary based on your car and where you get the repair done.