P0447 Code: Evaporative Emission Control System Vent Control Circuit Open

What the P0447 code means

The vent valve lets clean air into the charcoal canister so the canister can release the fuel vapors it has stored. Under normal conditions it stays open, and it only closes during the few seconds when the system checks itself for leaks.

The P0447 code is stored when the computer detects that the control circuit is open: no current flows when it should.

Compared with P0449, which is the general code for this circuit, P0447 names the electrical condition and narrows the diagnosis quite a bit. An open circuit has only a few possible causes: a burned valve coil, a cut wire, an unplugged connector or a blown fuse.

What tips the odds toward the wiring is the location. That valve lives under the vehicle next to the canister, with five feet or more of wire exposed to rubbing, water, road salt and rodents. Before you order the part, it pays to follow that wire with a flashlight.

There is also a practical consequence to expect. If the valve cannot close, the system can never be sealed, and the leak test reports leaks that are not there.

It is worth understanding why a system that only handles vapors has so many components and sets so many codes. The regulations are not satisfied with simply trapping the fumes. They require the vehicle to prove on a regular basis that the system is closed, because a tank that breathes to the outside releases hydrocarbons even when every part is installed. That requirement means the system has to be sealable on demand, and that is why there is a vent valve, a pressure sensor and a set of test routines. All of that hardware exists only to prove the system is airtight, not to make the engine run any better.

It also helps to understand why this valve rests open and not closed, which is what most people would expect. If it stayed closed when it failed, the tank could not breathe. As fuel is used, a vacuum would build up inside, and that vacuum could end up collapsing the tank or keeping the fuel pump from drawing fuel.

Leaving it open by default guarantees the system can always equalize pressure even if the electronics fail. The price of that design choice is that an open circuit leaves the system permanently vented and unable to seal, which is exactly what this code describes and the reason it drags leak codes along with it.

P0447 code symptoms

• Check engine light on.
• EVAP leak codes showing up at the same time even though there is no real leak.
• Trouble filling the tank, with the pump nozzle shutting off over and over.
• The EVAP monitor never reaches ready status.
• Failed emissions test.
• The engine runs the same as always.
• A sucking noise when you open the gas cap.
• The system stays permanently vented and never manages to seal for the test.

Likely causes of the P0447 code

1. Cut or broken wiring along its path under the vehicle. A very common cause because of the exposure.
2. Open valve coil.
3. Connector unplugged, corroded or with backed-out pins.
4. Blown fuse in the circuit.
5. Rodents chewing the harness near the fuel tank.
6. Water getting into the connector.
7. Open ground in the circuit.
8. Damaged output driver in the computer. The last possibility.
9. Harness hanging loose from its clips, which ends up rubbing or snagging on things.

How to diagnose the P0447 code step by step

1. Locate the valve, normally next to the canister near the fuel tank.
2. Raise the vehicle and follow the wire along its whole path. This is the check that solves the most cases with this code.
3. Measure the valve coil resistance with the connector unplugged. An infinite reading confirms an open coil.
4. Check that 12 volts reach the supply pin with the key on.
5. Verify continuity of the control wire all the way to the computer.
6. Inspect the connector for water, green corrosion and backed-out pins.
7. Check the circuit fuse.
8. Command the valve with an active test and listen for the click.
9. Check that all the harness clips are present along the route to the valve. A missing one leaves the wire exposed to rubbing and pulling.

How to fix the P0447 code

• Repair cut wiring with solder and sleeving rated for underbody use, and secure it along the original routing.
• Replace the valve if its coil is open.
• Clean or replace the corroded connector and protect it with dielectric grease.
• Replace the fuse and find out why it blew.
• Protect the harness if rodents have damaged it.
• Restore the circuit ground.
• Secure the harness to the original routing with new clips so the wire does not break again.

Fix this code before chasing any associated leak code. Those leak codes often go away on their own because the leaks never existed.

Technical reference data

• Typical valve coil resistance: 20 to 40 ohms. Infinite means an open coil.
• Resting state of the valve: open. It only closes during the leak test.
• 12 volt supply with the ground controlled by the computer.
• An incomplete seal produces false leak codes.
• P0449 is the general code for the same circuit.
• The valve rests open by design so the tank can equalize pressure even if the electronics fail.

Brand-specific notes

Before you order the valve, spend ten minutes following the wire with a flashlight. Because of its route under the vehicle, the wiring fails more often than the coil, and the repair costs a fraction of what the part costs.

When this code shows up alongside a leak code, always fix the vent circuit first. A valve that cannot close keeps the system from sealing, and the computer reports leaks that do not actually exist.

Frequently asked questions about P0447