P0499Generic code

P0499 Code: Evaporative Emission System Vent Control Circuit High

The P0499 code indicates high voltage in the EVAP vent valve control circuit, from an open circuit or a short to voltage. Check the fuse, relay, connector and wiring before replacing the valve. The code usually does not affect driving.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$30 to $250
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0499 code means

The vent valve lets clean air into the canister and closes during the leak test. It is open at rest, and the computer closes it when it needs to seal the system.

The computer monitors the control circuit from its own driver transistor. The P0499 code indicates high voltage in the control circuit (an open circuit or a short to voltage). Before replacing the component, check the fuse, relay, connector and wiring, since they are the most common cause.

The valve usually sits next to the canister under the vehicle, exposed to dust and water. A valve that will not open makes the pump nozzle shut off while you fuel up, and one that will not close makes the leak test impossible.

To confirm it, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be less than 1 ohm, and an infinite reading means the wire is open. If the wiring is good, measure the component itself: infinite resistance confirms it is open inside.

P0499 code symptoms

  • Check engine light on.
  • The pump nozzle shuts off while fueling.
  • EVAP monitor incomplete.

Likely causes of the P0499 code

  1. Connector loose or broken. The most frequent cause, especially after another repair in the area.
  2. Open coil or motor, with infinite resistance in the component.
  3. Control wire cut between the component and the computer.
  4. Short to 12 V, where the control wire touches another wire that carries voltage.

How to diagnose the P0499 code step by step

  1. Command the component with the scan tool and check whether it responds.
  2. Check the fuse and relay.
  3. Measure the supply at the connector: battery voltage with the key on or when it is commanded.
  4. Measure the component resistance and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity and for shorts.
  6. Inspect the vent filter and clean off any dirt.
  7. Power it with 12 V. It should close with a click.

How to fix the P0499 code

  • Repair the connector, the wiring or the power supply.
  • Replace the EVAP vent valve if it does not respond with correct power and control.
  • Clear the codes and verify that the monitor completes.

Technical reference data

  • 12 V solenoid; approximate resistance 20 to 30 ohms.
  • Approximate values only: check the manufacturer data for your engine.

Brand-specific notes

The vent valve normally sits next to the canister under the vehicle, so start with the connector and the wiring before you buy the part.

P0499 on GM

On GM vehicles the vent valve often gets clogged on vehicles that are driven on dirt roads.

P0499 on Toyota

On Toyota vehicles the vent valve often gets clogged on vehicles that are driven on dirt roads.

Frequently asked questions about P0499

Can I drive with a P0499 code?
Yes. A P0499 code normally does not affect driving. Repair it before your emissions inspection.
What does the EVAP vent valve do?
The vent valve lets clean air into the canister and closes during the leak test. It is open at rest, and the computer closes it when it needs to seal the system.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first.
How much does it cost to fix P0499?
Roughly $30 to $250, depending on whether it is wiring or the valve itself.
What does the P0499 code mean?
It is a generic OBD2 code that means the EVAP vent valve control circuit is reading high voltage, from an open circuit or a short to voltage.
What is the most common cause of P0499?
A loose or broken connector, especially after another repair in the area. An open coil and a cut control wire come next.

Related codes

Questions about the P0499 code

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