EVAP Vent Valve Control Circuit High
The P0499 code indicates that the Powertrain Control Module (PCM) has detected a high voltage condition in the control circuit of the Evaporative Emission (EVAP) system vent valve. This valve is responsible for sealing the EVAP system during leak testing. A high voltage reading typically points to a short to power, a faulty vent valve solenoid, or a wiring issue. The EVAP system prevents fuel vapors from escaping into the atmosphere, so this fault can trigger the Check Engine Light and may cause a failed emissions test.
01. Most Common Causes
- Faulty EVAP vent valve solenoid
- Short to power in the vent valve control circuit
- Damaged wiring or connector at the vent valve
- Corroded or loose electrical connections
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Possible failed emissions test
- No noticeable drivability issues in most cases
- Fuel odor in some cases
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0499 and check for other EVAP codes.
Step 2: Visually inspect the vent valve and its wiring for damage, corrosion, or loose connections.
Step 3: Disconnect the vent valve connector and measure voltage at the harness with the ignition on. Should be near 0V. If battery voltage is present, there is a short to power.
Step 4: Test the vent valve solenoid resistance (typically 20-40 ohms). Replace if out of spec.
Step 5: If wiring and valve are okay, check for a faulty PCM or perform a continuity test from the PCM to the valve.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but the Check Engine Light will remain on and the vehicle may fail an emissions test. It is recommended to repair it promptly to avoid potential fuel vapor leaks.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the vent valve or wiring needs replacement. DIY replacement of the valve is often under $50.