What P0499 means
P means powertrain (engine and transmission). The 0 marks a generic code defined by SAE, so the same number means the same thing across makes. The third character, 4, places it in the auxiliary emission controls subsystem; the last two digits identify the specific fault.
The vent valve sits near the charcoal canister and lets fresh air in or out of the EVAP system. The engine computer closes it to seal the system for leak tests. It is exposed to dirt and water on many vehicles.
What “Circuit High” means here
"High" means the signal or control voltage rose above the maximum the module expects. For a controlled component such as a solenoid, relay or motor, "high" means the voltage on the control circuit is higher than expected for the commanded state — commonly an open circuit or a short to voltage, depending on how the circuit is switched.
What you may notice
Symptoms depend on the vehicle and on how the module responds to the fault. Any of these can accompany P0499:
- Usually none
- Difficulty refuelling (pump nozzle clicking off) if the vent is blocked
- Fuel smell
Where to start diagnosing P0499
- Inspect the vent valve and its filter for dirt, water or spider webs.
- Check the connector and solenoid resistance.
- Command the valve closed with a scan tool and listen for it.
Clear the code only after recording freeze frame data: it shows the engine speed, load and temperature at the moment the fault set, which is often the best clue to reproducing it.
Live data to watch
These standard OBD2 values relate to P0499. Support varies by vehicle; a value your car does not report will simply be missing.
| Value | What to look for |
|---|---|
| EVAP system vapour pressure (PID 0x32) | Should change when the vent closes during a test. |
Related codes
Codes from the same EVAP vent valve family. If several are stored together, the shared part — wiring, a common reference voltage, or the component itself — is the place to start.
| Code | Definition |
|---|---|
| P0446 | Evaporative Emission System Vent Control Circuit Malfunction |
| P0447 | Evaporative Emission System Vent Control Circuit Open |
| P0448 | Evaporative Emission System Vent Control Circuit Shorted |
| P0449 | Evaporative Emission System Vent Valve/Solenoid Circuit |
| P0498 | Evaporative Emission System Vent Valve Control Circuit Low |
Further reading
Frequently Asked Questions
What does P0499 mean?
P0499 is the generic SAE J2012 code for "Evaporative Emission System Vent Valve Control Circuit High". In plain terms, it means the engine computer has detected a "circuit high" fault on the EVAP vent valve.
Can I keep driving with P0499?
Drivable; may affect refuelling and inspection readiness.
What should I check first for P0499?
Inspect the vent valve and its filter for dirt, water or spider webs.
Definition source: SAE J2012 / ISO 15031-6 generic DTC definitions. This is the generic meaning that applies across makes; a manufacturer can define a code more narrowly or add its own sub-codes, so confirm against the service information for your vehicle before replacing parts. Written by the OBDAssistant engineering team — see our editorial policy.