P0446 Code: Evaporative Emission Control System Vent Control Circuit
The P0446 code means the vent valve that lets clean air into the charcoal canister is not responding the way the computer expects. Because the valve sits under the vehicle, dirt, moisture and insects cause a big share of these cases. It is a low severity code and you can keep driving, but it often makes the fuel nozzle shut off at the pump.
- Severity
- Low
- Can I keep driving?
- Yes, no immediate risk
- Estimated cost
- $30 to $300
- Difficulty
- Easy
- System
- Emissions Control
- Applies to
- All OBD2 vehicles
On this page
What the P0446 code means
For the charcoal canister to release the fuel vapors it holds, clean air has to come in through the other end. That is the job of the vent valve, which stays open under normal conditions.
The same valve has a second job: it closes when the computer wants to seal the system to check for leaks. Without that closing, a leak test is not possible.
The P0446 code is set when the control circuit of that valve does not respond or when the valve cannot close. Its usual location, near the canister under the vehicle, exposes it directly to mud, road salt, dust and even insects that nest in the air intake filter.
It helps to understand why this valve stays open at rest and not the other way around. If it stayed closed, the fuel tank could not make up for the pressure changes caused by temperature swings and by the fuel being used. The tank would end up deforming or pulling a vacuum that keeps the fuel pump from drawing fuel.
That is why its rest state is open, and it only closes for the few seconds the leak test lasts. When it fails mechanically, it usually stays open, which keeps the system from sealing and makes it report leaks that do not exist. That is the reason a P0446 code so often drags false leak codes along with it.
P0446 code symptoms
- Check engine light on.
- Trouble fueling: the pump nozzle clicks off again and again.
- A sucking or hissing noise when you open the fuel cap.
- Gasoline smell near the rear of the vehicle.
- The EVAP monitor never reaches ready status.
- Failed emissions test.
- EVAP leak codes that show up at the same time even though there is no real leak.
- A sharp thump from the tank when you open the cap after a hot day.
Likely causes of the P0446 code
- Vent valve clogged with dust, mud or insects. Very common because of where it is mounted.
- Vent valve coil open or shorted.
- Connector corroded by moisture and road salt.
- Damaged wiring under the vehicle.
- Clogged system air intake filter.
- Saturated canister, which blocks the airflow.
- Vent hose crushed or pinched, for example after work done underneath the vehicle.
- Canister air filter completely plugged with dried mud, common on vehicles driven on dirt roads.
- Weak spring inside the valve, which keeps it from closing fully.
How to diagnose the P0446 code step by step
- Locate the vent valve, normally next to the canister, near the fuel tank.
- Inspect its air inlet visually. Look for mud, spider webs, insect nests and a clogged filter.
- Command the valve with the scan tool and listen for the closing click.
- Measure its resistance with the connector unplugged and compare it with the specification.
- Check power and ground at the connector with the ignition on.
- Inspect the wiring along its whole path under the vehicle, watching for rubbing and corrosion.
- Blow through the valve. At rest it must let air pass, and when you apply voltage it must close completely.
- Check whether leak codes are also stored. A vent valve that does not close keeps the system from sealing and creates false leak codes.
- Check the canister inlet filter. On vehicles driven on dirt roads it plugs up with dried mud until air cannot get through.
How to fix the P0446 code
- Clean the valve and its air inlet if dirt has built up. In quite a few cases this clears the P0446 code without replacing anything.
- Replace the valve if its resistance is out of range or it does not close when voltage is applied.
- Replace the system air intake filter if it is clogged.
- Clean or replace the corroded connector and protect it with dielectric grease.
- Repair damaged wiring with protection suited to the underside of the vehicle.
- Replace the vent hose if it is crushed.
- Clean or replace the canister air intake filter, especially on vehicles driven on unpaved roads.
- Replace the valve if the internal spring cannot close it fully, and confirm it with the blow test.
- Reposition the vent hose if it is pinched and protect it so it does not get stepped on or crushed again.
Technical reference data
- Typical vent valve resistance: 20 to 40 ohms.
- Rest state: open. It only closes when the computer commands it.
- 12 volt supply with the ground controlled by the computer.
- A faulty seal keeps the leak test from running and leaves the EVAP monitor in a not ready state.
- Valve rest state is open. It only closes during the leak test.
- Coil resistance: 20 to 40 ohms.
- An incomplete seal creates false leak codes, so always repair this code before chasing leaks.
Brand-specific notes
If the pump nozzle keeps shutting off while you fuel, suspect this circuit before you suspect the tank. A vent that does not open keeps air from escaping while gasoline goes in, and the nozzle reads that as a full tank.
When a P0446 code and a leak code show up together, always repair the vent first. It is very common for the leak code to disappear on its own, because the leak never existed: the system simply could not seal the circuit to measure it.
Questions about the P0446 code
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