P0499
UniversalEvaporative Emission System Vent Control Circuit High
Low SeverityThis code indicates that the Powertrain Control Module (PCM) has detected an abnormally high voltage reading in the electrical circuit for the Evaporative Emission System's vent control valve. This typically suggests an electrical short to voltage in the wiring or a fault within the vent valve itself, preventing it from operating correctly and affecting the EVAP system's ability to manage fuel vapor. The only common symptom for the driver is the illumination of the Check Engine Light.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical work or working near fuel lines. Allow the engine to cool completely before inspecting or replacing components that may be hot. Fuel vapors are highly flammable, so ensure adequate ventilation and no open flames or sparks when working on the EVAP system.
Common Symptoms
- Check Engine Light illuminated
- Difficulty passing an emissions inspection
Common Causes
- Faulty Evaporative Emission (EVAP) system vent control valve
- Short to voltage in the EVAP vent control circuit wiring
- Corroded or loose electrical connectors at the vent valve or PCM
- Internal fault within the Powertrain Control Module (PCM) (less common)
Frequently reported on: 2007-2014 Chevrolet Silverado, 2005-2010 Honda Odyssey, 2006-2011 Toyota Camry, 2008-2012 Ford F-150, 2005-2009 Dodge Grand Caravan
Diagnostic Steps
- Visually inspect the EVAP vent valve and its wiring harness for any signs of physical damage, corrosion, or disconnected connectors. Pay close attention to areas where wiring might rub against chassis components, leading to a short.
- Locate the EVAP vent valve, typically found near the charcoal canister, which is often under the vehicle near the fuel tank or in the engine bay. Disconnect its electrical connector.
- Using a multimeter, test the voltage at the vent valve connector's power supply wire with the ignition on. Compare the reading to your vehicle's service manual specifications to confirm an abnormal high voltage.
- If the wiring appears intact and the voltage is consistently high, the EVAP vent valve itself may be internally shorted or stuck open. Attempt to replace the vent valve with a new, OEM-quality part.
- After replacement, clear the P0499 code using an OBD-II scan tool and perform a test drive to ensure the repair is successful and the code does not return.
👨🔧 When to Call a Professional
If you lack experience with electrical diagnostics using a multimeter or are unsure about locating and testing the EVAP system components, it is best to consult a certified automotive technician. Improper diagnosis or repair could lead to further electrical issues or an improperly functioning emissions system.
Commonly Asked Questions
What specifically does P0499 indicate about my vehicle?
P0499 indicates an electrical issue in the EVAP vent control circuit, specifically that the circuit's voltage is abnormally high. This often means a short to voltage or a faulty vent valve.
Will a P0499 code affect my car's performance?
Generally, a P0499 code will not directly affect your vehicle's drivability or performance. Its primary impact is on emissions control and the illumination of the Check Engine Light.
Where is the EVAP vent valve located?
The EVAP vent valve is usually found near the charcoal canister, which is commonly located under the vehicle, often close to the fuel tank, or sometimes within the engine compartment depending on the vehicle model.
Is it important to fix a P0499 code right away?
While not a critical safety issue, it is important to address a P0499 code to ensure your vehicle's emissions system is functioning correctly and to avoid failing future emissions tests.
What tools are needed to diagnose P0499?
You will need an OBD-II scan tool to read and clear the code, and a multimeter to test for voltage and continuity in the EVAP vent control circuit.