P0499: Evaporative Emission System Vent Control Circuit High

Definition

The OBD2 code P0499 indicates that there is a high voltage or an open circuit in the evaporative emission system vent control circuit, which can affect the system's ability to manage fuel vapors properly

Common causes

Faulty vent control valve
Wiring issues (short circuit or open circuit)
Poor electrical connections
Failed powertrain control module (PCM)
Blocked or restricted vent line
Vacuum leaks in the evaporative system
Corroded connectors or terminals

Common misdiagnoses

Faulty EVAP canister
Bad vent valve
Damaged wiring or connectors
Faulty fuel cap
Leaks in the EVAP system
Faulty PCM (Powertrain Control Module)
Incorrectly installed or damaged hoses

Troubleshooting steps

1. Check for Additional Codes

Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context for the issue
2. Inspect the Wiring and Connectors
3. Visually inspect the wiring and connectors associated with the evaporative emission system vent control valve. Look for signs of damage, corrosion, or loose connections
4. Pay special attention to the wiring harness leading to the vent control valve
5. Test the Vent Control Valve
6. Locate the vent control valve (usually found near the fuel tank or in the engine compartment)
7. Disconnect the valve and use a multimeter to check for continuity. If the valve is not functioning properly, it may need to be replaced
8. Check for Vacuum Leaks
9. Inspect the vacuum lines and hoses connected to the evaporative emission system for any leaks or cracks. A vacuum leak can cause incorrect readings and trigger the P0499 code
10. Inspect the Fuel Cap
11. Ensure that the fuel cap is properly sealed and in good condition. A loose or damaged fuel cap can lead to evaporative emission system issues
12. Test the Circuit Voltage
13. With the ignition on (engine off), use a multimeter to check the voltage at the vent control valve connector. Compare the readings to the specifications in the vehicle’s service manual
14. If the voltage is too high, there may be an issue with the vehicle’s electrical system
15. Check the PCM (Powertrain Control Module)
16. If all other components check out, there may be an issue with the PCM itself. This is less common, but it can happen. A professional diagnostic tool may be needed to check for PCM faults
17. Clear the Codes and Test Drive
18. After performing repairs or replacements, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns
19. Consult a Professional
20. If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic who has experience with the specific make and model of your vehicle. By following these steps, you should be able to identify and address the cause of the P0499 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Check for Additional Codes

2. Inspect the Wiring and Connectors

3. Visually inspect the wiring and connectors associated with the evaporative emission system vent control valve. Look for signs of damage, corrosion, or loose connections

4. Pay special attention to the wiring harness leading to the vent control valve

5. Test the Vent Control Valve

6. Locate the vent control valve (usually found near the fuel tank or in the engine compartment)

7. Disconnect the valve and use a multimeter to check for continuity. If the valve is not functioning properly, it may need to be replaced

8. Check for Vacuum Leaks

9. Inspect the vacuum lines and hoses connected to the evaporative emission system for any leaks or cracks. A vacuum leak can cause incorrect readings and trigger the P0499 code

10. Inspect the Fuel Cap

11. Ensure that the fuel cap is properly sealed and in good condition. A loose or damaged fuel cap can lead to evaporative emission system issues

12. Test the Circuit Voltage

13. With the ignition on (engine off), use a multimeter to check the voltage at the vent control valve connector. Compare the readings to the specifications in the vehicle’s service manual

14. If the voltage is too high, there may be an issue with the vehicle’s electrical system

15. Check the PCM (Powertrain Control Module)

16. If all other components check out, there may be an issue with the PCM itself. This is less common, but it can happen. A professional diagnostic tool may be needed to check for PCM faults

17. Clear the Codes and Test Drive

18. After performing repairs or replacements, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

19. Consult a Professional

20. If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic who has experience with the specific make and model of your vehicle. By following these steps, you should be able to identify and address the cause of the P0499 code