Short answer
A vent valve that didn't respond
A P0446 code says the car told the vent valve to do something and didn't see it happen. That's a different accusation from the leak codes and comes from a different part of the regulation, so checking the gas cap first, the right first move for a leak code, is the wrong first move here. The national EVAP repair averages $172, though that's the purge valve rather than the vent valve this code names, against the $1,511 converter people assume a check engine light means.
OilAndMiles.com - Search a P0446 code, or any EVAP code, and the same paragraph comes back: check the gas cap, then the purge valve, then the vent valve. For P0455, P0442 and P0456 that advice is sound, because those three are one test measured at three hole sizes and a loose cap really is the most common answer.
P0446 isn't in that group. Neither are P0441, P0443, P0449, P0451, P0452 or P0496. P0440 sits slightly apart again, a general evaporative fault rather than a named component, and it can turn up beside either group.
The valve codes come from a separate set of checks written into a separate section of the rule, and the difference isn't academic. A leak code says the system won't hold; a valve code says a component didn't respond.
Which of the two tests does your code come from?
California's OBD II regulation is the one the EPA accepts in place of its own, so it is what almost every car sold in the United States is built to. Its evaporative system requirement opens like this:
The OBD II system shall verify purge flow from the evaporative system and shall monitor the complete evaporative system, excluding the tubing and connections between the purge valve and the intake manifold, for vapor leaks to the atmosphere.
Then it lists exactly three system faults: no purge flow at all, a leak the size of a 0.040 inch orifice, and a leak the size of a 0.020 inch one. That's the whole system level test. Nothing in it mentions a vent valve, a solenoid or a circuit.
The very next sentence sends the parts somewhere else. Valves and sensors are named as individual components and handed to the comprehensive components section, which tests four things rather than one. Its wording is in the panel at the foot of this page.
Those four checks are the valve codes. Not a summary of them, the source of them.
| Which test | What it covers | What it looks for |
|---|---|---|
| Section (e)(4) | The system, three faults | No purge flow at all, a 0.040 inch leak, or a 0.020 inch leak. That's the whole system-level test, and nothing finer |
| Section (e)(15) | Each part, four checks | Circuit continuity, out-of-range values, rationality, and proper functional response. The valve codes are written here, not in the leak test |
| The purge valve | Named in the rule | Purge flow is one of the three system faults, so every car sold has to verify it |
| The vent valve | Never named at all | The regulation doesn't mention it once. P0446 and P0449 exist because makers were allowed to split codes for technicians, not because the rule asked |
We went to the regulation itself for this rather than to a code lookup, because the lookups repeat each other and none of them explains why a vent valve has a code at all. The rule never asks for one, and that's the thing worth knowing about P0446.
This split is why gas cap advice misfires here. A gas cap is a leak. These codes are a valve that didn't do what it was told.
Which of the four accusations is yours?
P0446 is the fourth kind, and the difference decides what you buy. An EVAP monitor reports four kinds of fault: two about the wiring or the sensor, one about a reading that doesn't fit its conditions, and one about a valve that was told to move and didn't.
| The accusation | Codes that carry it | What the computer actually did |
|---|---|---|
| Circuit continuity | P0443, P0449 | An electrical test only. The computer looks down the wire and finds an open, a short, or nothing. No opinion yet about the valve itself |
| Out-of-range values | P0452, P0453 | The pressure sensor is reporting a number that isn't physically possible. That points at the sensor or its wiring, not at the tank |
| Rationality | P0451 | The reading is possible but doesn't fit the conditions. Plausible on its own, wrong next to everything else the car knows |
| Functional response | P0441, P0446, P0496 | The computer told the valve to move, watched for the change, and didn't see it. The wiring can be perfect and this still fails |
The practical consequence is where you start. A circuit code is a wiring fault until proven otherwise: connector, corrosion, a chafed wire, and only then the solenoid. A functional response code is the opposite: the circuit already passed, so the problem is the part, or the passage the part controls.
What are the two valves actually told to do?
The purge valve sits between the charcoal canister and the intake. Fuel evaporates in the tank whether the car is running or not, the canister catches those vapors, and when the engine is in a state that can take them the computer opens the purge valve and the stored vapor is drawn in and burned. With the engine off it stays shut.
The vent valve does the opposite job. It's normally open so the canister can breathe, and it closes only when the car wants to seal the system to test it. Sealing is the whole reason it exists.
Use this image
Free to republish under CC BY 4.0: credit Oil & Miles and link to this page. The snippet does both.
<a href="https://oilandmiles.com/articles/p0446-code"><img src="https://oilandmiles.com/assets/img/diagrams/p0446-no-answer.svg" alt="Line diagram of the vent branch of the fuel vapor system: the charcoal canister, the vent valve hanging under it with its connector and its fresh air opening breathing both ways, and the engine computer. A solid line carries the order to close the vent and reaches the valve with a filled arrowhead. A hollow line carries the answer back from the tank pressure sensor, whose needle hasn't moved, and stops short of the computer at an empty dashed box" width="1000" height="740"></a> <p>Diagram: <a href="https://oilandmiles.com/articles/p0446-code">Oil & Miles</a>, CC BY 4.0</p>| The valve, or how it failed | What that does | What you get |
|---|---|---|
| Purge valve | Opens to burn the vapor | Between the charcoal canister and the intake. It opens when the engine can take the vapor, which is then burned. Shut with the engine off |
| Purge stuck shut | Vapor has nowhere to go | The canister fills and stays full. Purge flow reads zero, and that's one of the three faults the regulation names outright |
| Purge stuck open | Vapor arrives uninvited | Raw vapor enters at idle. That can show up as a rich code, an unsteady idle, or a hard restart right after refueling |
| Vent valve | Closes to seal for the test | Normally open so the canister can breathe. It shuts only when the car wants to seal the system and test it |
| Vent stuck open | The test can't finish | Nothing holds pressure, so the car may report a leak it doesn't have, or never complete the check at all |
| Vent corroded | Why this one fails | It usually hangs under the car near the canister, in the path of road salt and standing water. Position kills it, not design |
One failed part can raise two codes. A vent valve that won't seal makes the purge check unreliable in the same breath.
That difference explains why the vent valve is the one that rots. It hangs under the car near the canister, in the path of road salt and standing water, while the purge valve lives in the engine bay. Position kills it, not design.
It also explains a pairing that confuses people. If the vent valve won't seal, the car can't complete a test that depends on sealing, so a single failed part can raise a vent code and make the purge check unreliable in the same breath. Two codes, one repair.
What do P0441 and P0449 say that P0446 doesn't?
Those two arrive often enough, and beside P0446 often enough, to be worth taking on their own terms. They sit on the same grid, one square over each.
P0441: the flow is wrong in either direction
Incorrect isn't the same word as absent, and the difference is the whole code. P0441 covers flow arriving when the valve was told to be shut, as well as no flow when it was told to open. Most descriptions of it only mention the second.
That's also why P0441 is the one member of this family that can come with something you notice. Raw fuel vapor arriving at idle, from a valve that won't close, can make the idle uneven or the restart difficult straight after a fill-up. Everything else here changes nothing you can feel.
What is blocking it is frequently not the valve. When a charcoal canister begins to break down, the pellets inside get drawn into the purge line and clog the valve or the line itself.
Replace the valve alone and the new one meets the same charcoal. On 2002 to 2007 Dodge and Chrysler vehicles there is a different known cause again: the natural vacuum leak detection assembly, which isn't a purge valve at all.
Samarins, an independent repair reference, reports a 2003 Toyota bulletin naming an inoperative canister closed valve VSV as a cause of P0441 and P0446 together. We couldn't open the bulletin itself, so treat that as a lead worth giving your technician rather than as a fact we have checked. It would explain the pairing described earlier from the other direction.
P0449: the wire, not the valve
P0449 and P0446 are the same physical part accused of two different things. P0446 is proper functional response: the computer commanded it and didn't see the change. P0449 is circuit continuity: the computer looked down the wire and found an open, a short, or nothing on the end of it, and has formed no opinion about the valve at all.
That distinction earns its keep here more than anywhere else in the family, because the vent valve is the one component that hangs under the car near the canister, in the path of road salt and standing water. Its connector is exposed in a way that nothing in the engine bay is.
So on P0449, the connector deserves more of your attention than the solenoid, and looking at it costs nothing. If P0446 and P0449 are both present, start there rather than treating them as two faults: a corroded connector can raise the circuit code and stop the valve responding in the same moment.
Why does the same code point at different hardware?
Because the fine grained codes were permitted rather than required, so each maker drew the lines its own way. The regulation lets a manufacturer monitor portions of the system separately, and approves it on one condition: that the split gives a technician better isolation of the fault.
That's the whole point of them. The fine grained codes exist for whoever is holding the scan tool, and the carving up was the manufacturer's decision. The federal floor is three faults; six or seven codes is a maker being more specific than it had to be.
So the naming drifts: Toyota calls these solenoids vacuum switching valves, and its own documentation uses VSV where a generic list says purge valve. GM doesn't use the words vent valve either: Chevrolet's own emission warranty parts list names a canister vent solenoid, and GMC's, four years older, lumps it in with the other canister solenoids. Chrysler ran a natural vacuum leak detection assembly that combines functions other makers keep separate, so the code number is standard and the thing behind it is not.
Which means a generic code definition is a starting point and not an answer. Before buying a part, find what your manufacturer calls the component that code refers to on your engine. This is the step most people skip, and it's the one that turns one repair into two.
Why does a P0446 code come back faster than a leak code?
Because the purge check is required to run about twice as often as the small leak check. The regulation sets how often each monitor has to run, as a ratio against driving cycles. The two numbers aren't the same:
- 0.520 for purge flow and 0.040 inch leak detection
- 0.260 for 0.020 inch leak detection
The purge check is required to run about twice as often as the very small leak check. That has a direct consequence for anyone who just cleared a code.
If the fault is a purge or vent problem and it hasn't been fixed, the light comes back quickly. A very small leak can take considerably longer to catch you out, which is the mechanism behind the repair that looked like it worked and then didn't, covered in our article on whether a P0456 clears itself.
Turn that around and it's useful. On these codes, a light that stays off after a repair is a stronger signal than it would be on P0456. The car is checking more often.
What the data says
There's a second way this code comes back, and one manufacturer has documented it for twenty-one years. GM tells its dealers that trucks worked in dusty conditions draw dust into the evaporative system until it plugs the canister and the canister vent solenoid, setting P0442, P0446, P0455 or P0449.
The fix it publishes isn't a new valve. It's an in-line filter retro-fitted between the canister and the air inlet, and GM says the filter itself has to be checked periodically or the code sets again. It also says twice that this isn't warranty work and the owner pays.
GM bulletin 23-NA-073, version 5, March 13, 2025, covering the Silverado and Sierra 1500, 2500HD and 3500HD for 2019 to 2025. First released June 2023 and revised four times since, twice only to add newer model years. Read through NHTSA's bulletin archive, September 19, 2026. The archive holds the same finding under two earlier GM numbers, from 2004 and 2010, with no document attached to either.
What does the national complaint record say?
Almost nothing, and that's the answer. A hundred and sixteen complaints in the whole file name any of these codes, against 422 for a single misfire code, and P0446 itself appears four times. Nobody is filing about this, which is worth knowing before you spend money fearing it.
From the national complaint record
116
complaints name any of these codes, out of 645,169 scanned. One misfire code, P0302, appears in 422.
| P0496, high purge flow | 35 |
|---|---|
| P0441, purge flow incorrect | 27 |
| P0451, pressure sensor range | 15 |
| P0443, purge control circuit | 12 |
| P0449, vent valve circuit | 12 |
| P0452, pressure sensor low | 11 |
| P0446, vent control | 4 |
That gap isn't a sampling accident. A code in this family changes nothing about how the car drives, so almost nobody writes to the federal government about it. They see a light, and that's the whole experience of it.
What does a P0446 code cost?
CarMD's Vehicle Health Index for 2026, drawn from 39,116,755 repairs across the 2025 calendar year, puts replacing the EVAP canister purge control valve at $172, the sixth most common repair in the country and 4.93% of all of them. It's also the cheapest entry on that national top ten. CarMD sells diagnostic tools, which is an interest worth naming, though the ranking is drawn from repair records rather than from anything it sells.
What a P0446 code costs against what people fear
Two outcomes, so there's no total: one is what this code usually means, the other is what people fear it means.
| EVAP canister purge control valveSixth on the national list and 4.93% of 2025 repairs | $172Parts and labor, US average |
|---|---|
| Catalytic converterFirst on the list, and what people assume a check engine light means. Nearly nine times the bill | $1,511Parts and labor, US average |
CarMD Vehicle Health Index 2026, US averages across 39,116,755 repairs recommended in 2025, parts and labor together.
That makes this an unusual code to write about, because the honest headline is good news. The vent valve itself is cheaper again: across the four vehicles we priced for P0455 it ran $15 to $85 at the counter, which is the part alone rather than the fitted job the $172 describes. Compare that with a converter, which averaged $1,511, and the gap is nearly nine to one.
There's no symptom to weigh, either. An EVAP fault costs the atmosphere, not the driver: no power loss, no noise, no drivability change of any kind.
That's exactly why it feels like an invented repair. It's not one. In a state that runs an emissions test, the car will fail it, and the light hides anything more serious that arrives later.
What should you do about a P0446 code?
Four steps for working out what your car means by this code before you buy a part for it, in order, because the free ones come first. 4 steps below:
- Read the freeze frame data. That is the snapshot of engine conditions the computer saved at the moment the code set, and any scan tool that reads codes will show it. Note every code present, not just the one you came for.
- Look up what your manufacturer calls the part that code names. Toyota's VSV and a generic list's purge valve can be the same component.
- Inspect the vent valve and its connector for corrosion. It is the cheapest thing to find and the most exposed.
- Only then start replacing anything. The three checks above cost nothing, so a part bought before them is a part bought on a guess.
And if you have a leak code alongside, see how to read the codes together.
From the documents
What does the regulation actually say about the vent valve?
Nothing. It never names the part. The rule sets out what has to be watched, then hands the individual components to a different section with a different set of tests.
Separately, it lets a manufacturer split the system into codes of its own. Those two sentences are why P0446 exists and why it sits outside the leak group, and neither of them is about a leak at all.
California Code of Regulations, Title 13, section 1968.2
for circuit continuity, out of range values, rationality, proper functional response, etc.
California Code of Regulations, Title 13, section 1968.2
provides further isolation of the malfunction for repair technicians by utilizing separate fault codes for each monitored portion of the evaporative system
Conclusion
The accusation is a part, not a hole
This code accuses a part, not a hole. The car told the vent valve to move and didn't see it happen, which is a different test from the leak codes and points at different hardware. That's also why the honest headline here is good news rather than bad.
There's no symptom to weigh against it either: an EVAP fault costs the atmosphere, not the driver, with no power loss and no noise of any kind. Oil & Miles says when a code is cheap as readily as when it's not, across repair costs.
Common questions
Asked most often
What does P0446 mean on a Chevy Silverado?
The same thing it means on any other car. What changes with the badge is vocabulary: GM's emission warranty parts list names a canister vent solenoid, not a vent valve, so the scan tool and the invoice need not agree. We can't tell you it fails more often on a Silverado, because the complaint record above doesn't support it.
What does the :00 after P0446 mean?
Two extra digits some manufacturers print after a diagnostic trouble code, or DTC. GM calls it a symptom byte, and it narrows what failed. We counted every service bulletin in the federal archive: 216 codes appear with one, and 29 carry several. What each value means isn't published anywhere we could read.
What does the P0446 code mean?
The car commanded the evaporative system vent control and didn't observe the response it expected. It's a functional response fault, not a leak measurement. What the vent control physically is varies by manufacturer.
Will a new gas cap fix P0446?
Almost certainly not: a gas cap is a sealing surface, and a loose one shows up as a leak code such as P0455, P0442 or P0456, or as P0457, which exists for a cap left loose or off. P0446 is a component that didn't respond. Check the cap because it costs nothing, not because it's the answer.
Is it safe to drive with P0446?
Yes, in the sense that nothing about the car's running is affected. The system exists to stop fuel vapor reaching the atmosphere, so a failure costs the atmosphere rather than the engine. Two real consequences remain: the car will fail an emissions test where one is required, and a lit lamp can't warn you about anything that happens next.
Why do I have P0441 and P0446 at the same time?
Often one part. A vent valve that won't seal stops the system holding, and a purge flow check that depends on that seal then can't return a trustworthy result. Fix the sealing fault first and retest before treating them as two repairs.
How much does it cost to fix?
CarMD puts the purge control valve at $172, the cheapest repair on its national top ten. The vent valve is cheaper again, $15 to $85 at the counter, though that's the part alone. What catches people is replacing the wrong one, which is why identifying what your maker calls the part comes first.
What is the difference between P0446 and P0455?
Different tests entirely: P0455 is the system leak check reporting a hole at least as big as a 0.040 inch orifice. P0446 is a component check reporting that the vent control didn't do as it was told. When a car sets both, chase the vent fault first: a vent that won't close makes the leak test unreliable.
What people ask next
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Sources
- California Code of Regulations, Title 13, section 1968.2, read at source: subsections (e)(4.1), (e)(4.2.2), (e)(4.2.6) and (d)(3.2.1)(B). Every figure they carry is on the page above. California Air Resources Board, read August 26, 2026
- CarMD Vehicle Health Index 2026, read as the published PDF, for the purge valve price and its national ranking. CarMD sells diagnostic tools, an interest worth naming. CarMD.com Corp, read August 2026
- Samarins, an independent repair reference, for three P0441 findings we couldn't source elsewhere. It also reports a 2003 Toyota bulletin for P0441 and P0446, without a number; we couldn't open it, so that one is carried as a lead. Samarins.com, read August 26, 2026
- GM Limited Warranty and Owner Assistance Information, the Emission Warranty Parts List, for what GM calls the part. The 2020 Chevrolet book (GMNA-Localizing-U.S.-13338428) names a canister vent solenoid; the 2016 Chevrolet (GMNA-Localizing-U.S-9159214) and GMC (GMNA-Localizing-U.S-9159385) books lump it as canister solenoids and valves. General Motors, read September 19, 2026
- The counter price for the vent valve is our own census rather than an estimate: every brand RockAuto lists for a 2015 Silverado 5.3L, 4Runner 4.0L, F-150 5.0L and Altima 2.5L, set out in full in our P0455 article. Oil & Miles, read September 4 and 5, 2026
- GM bulletin 23-NA-073, for dust intrusion into the canister and vent solenoid on Silverado and Sierra trucks. Version 5, March 13, 2025. General Motors, read through NHTSA's archive, September 19, 2026
- NHTSA's service bulletin archive, all 259,419 records, read through the agency's own API for the suffix count and for what manufacturers call these parts. NHTSA, read September 19, 2026
- The leak codes and the thresholds behind them are set out with their federal source in our own P0456 article, including the conditions the leak test has to meet before it can run at all. Oil & Miles, September 2026
How this was compiled
The complaint counts come from NHTSA's published bulk download rather than its search page, so the whole record is counted rather than a sample. The file is FLAT_CMPL, and the copy read here is dated August 25, 2026.
NHTSA files one row per component a complaint names, so the count is by complaint number rather than by row: across the 2010 to 2025 model years that is 645,169 complaints, and those are what was scanned for this article.
The suffix count is ours and wasn't sampled. We pulled every record in NHTSA's service bulletin archive, 259,419 of them, and counted the codes printed with two extra digits: 3,066 uses across 216 base codes, of which 29 appear with more than one suffix. That last number is the one that matters, because a code carrying several suffixes is a code whose digits are naming different faults.
The search figures come from our own keyword export for this code, 1,000 queries read on August 26, 2026. Just over half the monthly volume carries a maker's name, and GM accounts for about two thirds of that half, typed as Chevy, Silverado, Chevrolet, GMC and Sierra, which is why GM is the one named in the text. The export says what people type, not what breaks.
The four checks that organize this article aren't our framework. They're the four phrases the regulation itself uses when it hands the valves and sensors to the comprehensive components section, and the code family maps onto them cleanly enough that no other grouping was needed. Reading the rule first is also what showed that the vent valve is never named in it, which is the fact the rest of the page rests on.
This page covers the valve and sensor codes as one family, because they're one system checked four ways and separate pages would repeat the same explanation with a different number in the title. One exception has since been made: P0443 has its own page, because the circuit test is the one accusation readers act on wrongly, and the argument needed more room than a paragraph inside a family article.
What we didn't do
- We name no failure rate by manufacturer. Search volume for these codes does cluster around particular makes, but complaint records don't support reading that as a difference in how often the part fails, and fleet size and forum habits explain the pattern at least as well. We describe the naming and the architecture, which are documented, and where a maker publishes a condition on its own vehicles we report it as theirs rather than as a comparison.
- We give no resistance value, voltage range or vacuum figure for testing a valve. Those are model specific, the numbers in circulation are copied between sites without a source, and publishing one as though it were general would be inventing a specification.
- We didn't scan a vehicle, smoke test a system or replace a valve for this article. The regulation and the repair data are read at source and cited; nothing here is presented as first hand experience.
- We recommend no brand of valve, cleaner or scan tool, here or anywhere on the site.
Prices are ranges compiled in August and September 2026 for the US market and vary by region, engine and shop rate. Prices from $10 up are rounded to the nearest dollar, so $14.13 reads as $14 and $14.52 as $15. Below $10 they're exact. This article is general information, not advice about your specific vehicle, see the disclaimer.