What Does P0499 Mean?
The PCM has detected that the EVAP system vent valve control circuit voltage exceeds the maximum expected threshold. This high circuit condition typically indicates an open in the vent valve solenoid coil, an open control wire, or a short to battery voltage in the circuit. The PCM cannot properly close the vent valve, which is required for EVAP leak detection and fuel vapor containment.
Common Causes
30%
Open circuit in the EVAP vent valve solenoid coil due to a burned or broken internal winding
30%
Broken or disconnected wire in the vent valve control circuit causing an open between the PCM and solenoid
25%
Corroded or disconnected vent valve electrical connector with poor terminal contact or backed-out pins
15%
Vent valve control wire shorted to a nearby battery voltage source in the wiring harness
Diagnostic Steps
1
Disconnect the EVAP vent valve and measure solenoid coil resistance. Expected 20-50 ohms. Open loop (OL) reading confirms a failed solenoid coil requiring valve replacement.
2
With the vent valve disconnected, check for battery voltage on the control wire at the harness connector. Battery voltage present indicates the wire is shorted to a power source in the harness.
3
Verify the ground circuit at the vent valve connector. Measure resistance from the ground pin to a known-good chassis ground. An open ground can cause high-voltage feedback on the control circuit.
4
Inspect the entire wiring harness route from PCM to vent valve for breaks, rodent damage, or disconnected splice connections. The vent valve is often remote from the PCM, requiring a long harness run that is prone to damage.
5
If wiring and solenoid are functional, command the vent valve closed via scan tool and monitor the control voltage at the PCM output pin. Verify the PCM can pull the voltage low to drive the solenoid.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The PCM has detected that the EVAP system vent valve control circuit voltage exceeds the maximum expected threshold. This high circuit condition typically indicates an open in the vent valve solenoid coil, an open control wire, or a short to battery voltage in the circuit. The PCM cannot properly cl...
The most common cause of P0499 (Evaporative Emission System Vent Valve Control Circuit High) is: Open circuit in the EVAP vent valve solenoid coil due to a burned or broken internal winding
Typical repair costs for P0499 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An uncontrollable vent valve prevents the EVAP system from sealing for leak checks and may allow fuel vapors to escape to the atmosphere. This is primarily an emissions concern with no direct safety hazard to vehicle occupants.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0499 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Evaporative Emission Control System (EVAP)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
