EVAP System Vent Control Circuit Open

What it means

The engine computer has detected that the vent valve circuit is open, meaning current cannot flow because of a broken wire, a disconnected connector or a failed coil. The computer then cannot close the valve to run the leak test, so the system usually stays open to the air.

Related codes: P0446P0448P0449P0455

Symptoms4

• Check engine light on.
• Usually no driving symptoms.
• A large-leak code may appear with it because the system cannot be sealed during the test.
• Failed emissions test.

Possible causes5

• Vent valve connector disconnected or corroded due to its location near the tank.
• Open internal valve coil.
• Broken wire in the supply or control circuit, especially under the vehicle.
• Blown fuse feeding the circuit on some vehicles.
• Faulty driver circuit inside the engine computer (rare).

How to diagnose5

1. Inspect the connector near the tank and confirm it is seated with sound terminals.
2. Measure the valve coil resistance; an infinite reading means it is open.
3. Check for voltage at the connector with the ignition on.
4. Check continuity of the control wire to the computer.
5. Check the circuit fuse.

How to fix5

1. Reconnect, clean or replace the connector.
2. Repair the broken wire and protect it from stones and water.
3. Replace the fuse after finding why it blew.
4. Replace the vent valve if its coil is open.
5. Clear the codes and confirm the valve works with a scan tool.

The cost is low for a connector or wire repair, and rises when the vent valve is replaced because reaching it near the tank takes longer.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions