P0446 Code on a GMC: EVAP Vent System Performance (GMC Guide)

P0446 on a GMC is the EVAP vent code. GM's 2004 truck tables called it "EVAP Canister Vent Blocked"; current GM documents call it "EVAP Vent System Performance." Either way it means the same thing: with the vent supposed to be open, the fuel tank pulled more vacuum than it should — so fresh air isn't getting into the canister freely. On Sierra and Yukon trucks that usually means dust, mud or water in the frame-mounted vent valve or its filter, a problem GM has bulletins for going back to the 2000s. And on the 2023-and-later Canyon, GM's newest bulletin says the cause can be nothing more than ice on the fuel tank pressure sensor — and tells technicians not to replace any parts.

What Does P0446 Mean on a GMC?

The charcoal canister that stores fuel vapor needs a fresh-air inlet. That inlet runs through the canister vent solenoid (CVS) and a filter or pre-filter, out to the atmosphere. During normal driving the vent stays open: as the engine purges vapor out of the canister, outside air flows in behind it, and the tank stays close to atmospheric pressure.

If the vent path is blocked — a plugged filter, a mud-packed hose, a valve stuck closed or corroded — purging pulls a vacuum on the tank instead. The engine computer sees that vacuum on the fuel tank pressure sensor and sets P0446.

Despite some generic descriptions calling P0446 a "control circuit" code, GM's GMC tables treat it as a performance (restriction) test. The electrical fault on the same valve is a separate code, P0449.

How GM Tests the Vent on a GMC

• 2004 truck table (Sierra, Yukon, Savana, Envoy XL V8 and 4.3L). With the vent commanded open, the test fails if tank vacuum reaches 7 inches of water for 2 seconds during the initial purge ramp, or 9 inches of water for 23 seconds during normal purge. It also checks for an abnormal reading right after a cold-start key-up. Fuel must be between 15% and 85%, and it runs on a cold start with coolant and intake air between 3.75 °C and 30 °C.
• 2019 Sierra and Yukon table (4.3L, 5.3L, 6.2L). With normal purge and the vent commanded open, the test fails if tank vacuum exceeds about 2,989 Pa (about 12 inches of water) for 5 seconds before 8 liters of purge volume have accumulated. It passes if the purge volume is reached first. Fuel must be between 10% and 90%, start-up intake air between 4 °C and 35 °C, and it runs once per cold start. It's a Type B, two-trip code.

Two practical points follow. First, the code depends on the tank pressure sensor reading correctly — a sensor fooled by water or ice can set P0446 with a perfectly clear vent. Second, because the test needs a cold start and a fuel level away from full or empty, it may take a few days to confirm a repair.

Which GMCs Set P0446

P0446 appears in GM's tables for gas-engine GMCs from the late 1990s onward — Sierra, Yukon, Yukon XL, Savana, Sonoma, Jimmy, Envoy, Canyon, Acadia and Terrain. Duramax diesels don't have a gasoline EVAP system. The GMCs that set it most often, by GM's own paper trail, are trucks: their vent valve and canister sit under the vehicle where they collect road dust and spray.

Sierra and Yukon Dust and Water Bulletins

15-06-04-002 (April 2015, 2011–2015 Sierra). GM explains that the CVS valve draws fresh air through a vent at the top of a conduit secured to the fuel filler pipe. Dirt and dust can restrict that path; water can reach the valve, corrode it, and restrict the fresh-air path when it closes. Water that overwhelms the valve's cyclonic filter can even reach the canister and restrict refueling. Customers often notice a hard-to-fill tank. GM installs a revised sealed CVS valve vented through a remote pre-filter mounted on the filler housing, using filter kit 23103351, and warns: do not replace the canister unless it fails the leak test or has ingested excessive dirt, dust or water.

09-06-04-028D (April 2014, 2007–2010 Yukon and Yukon XL 1500, including hybrids). Same mechanism, with moisture and corrosion at the valve. GM's fix is the revised CVS assembly 20995472 plus jumper harness 19257603.

23-NA-073 (March 2025, 2019–2025 Sierra 1500 and 2020–2025 Sierra HD). For trucks run in extremely dusty environments, dust can plug both the canister and the vent solenoid. GM adds an in-line filter between the canister and the air inlet (86792068 assembly, 86792069 foam filter), calls it a customer-pay alteration, and says the filter should be checked periodically like a maintenance item. Cab-and-chassis trucks are excluded.

The Canyon Ice Bulletin

GM's PIT6510 (April 2026) covers all 2023–2026 Canyons (and Colorados) with P0446 set current or in history, most often during seasonal changes or anywhere snow melts and refreezes. GM says water or snow dripping between the cab and bed can reach the fuel tank pressure sensor and freeze, blocking it, so P0446 sets at start-up.

The procedure: bring the truck into a space above 32 °F, access the top of the fuel tank, and clear and dry ice and water from around the sensor — removing the sensor cover if needed to dry the air reference port, but without removing the sensor itself. If there's no water or ice, or the code returns, technicians continue with normal P0446 diagnosis. GM’s instruction is plain: do not replace any parts for this issue.

This echoes an older bulletin. NHTSA's index lists GM bulletin 10-06-04-001 for 2009–2010 Canyon and Sierra, which adds a fuel tank pressure sensor cover because water or condensation can block the sensor's air reference port and set P0446 among other EVAP codes. We could read only the summary, so it's corroborated.

Symptoms of P0446

• Check engine light
• Fuel tank hard to fill; nozzle shuts off early
• Code appears in freeze-thaw weather (2023–2026 Canyon) or after dusty, muddy use (Sierra, Yukon)
• Often accompanied by P0442, P0455 or P0449 on Sierras and Yukons
• No change in how the engine runs

Causes and How to Confirm Each

How Is P0446 Diagnosed?

1. Read all codes and freeze frame. Note ambient temperature — a cold-weather P0446 on a Canyon points to PIT6510.
2. Check the tank pressure reading with the cap off. It should read near zero; if not, suspect the sensor or its reference port.
3. Inspect the vent path. Follow the fresh-air hose from the canister to its filter or pre-filter and look for dust, mud, insects and water.
4. Command the vent valve with a bidirectional scan tool and confirm it clicks and flows air when open.
5. Check your VIN against GM's bulletins — 15-06-04-002, 09-06-04-028D, 23-NA-073 or PIT6510 depending on model.
6. Repair the restriction, clear the code, and confirm with a cold start and fuel between a quarter and three-quarters.

Parts and Cost

GM Documents Relevant to P0446 on a GMC

Have a dealer check your VIN against current bulletins and campaigns rather than relying on any article, including this one.

What Other P0446 Pages Get Wrong

• Calling it a wiring code. On GMCs P0446 is a restriction test; the circuit fault is P0449.
• "Replace the vent solenoid." On a 2023–2026 Canyon, GM says the cause may be ice and to replace nothing.
• "Replace the canister." GM's truck bulletins say only if it fails testing or is contaminated.
• Ignoring the tank pressure sensor. The test relies on it; water or ice can fool it.
• Forgetting the filter after a retrofit. GM calls the 23-NA-073 filter a maintenance item.

Frequently Asked Questions

Can I drive with P0446?

Yes. It doesn't affect how the engine runs. A badly blocked vent can make the tank hard to fill and will fail an emissions inspection.

Why does my Canyon only get P0446 in winter?

GM's PIT6510 describes exactly that on 2023–2026 Canyons: melting snow drips between the cab and bed, refreezes on the fuel tank pressure sensor, and sets P0446 at start-up. Drying the area is the fix.

My Sierra is hard to fill. Is that P0446?

Often. GM's 15-06-04-002 links a hard-to-fill tank with P0446 and related codes on 2011–2015 Sierras, caused by dust or water in the vent valve.

Will cleaning the vent filter fix it?

If dust or mud is the restriction, yes. If the valve is corroded or the canister is full of water, GM's bulletins replace the valve or add a filter.

Is there a recall for P0446 on GMC trucks?

We found no recall. GM's truck documents are service bulletins, and 23-NA-073 is customer-pay. A dealer can check your VIN for any open campaign.

Does P0446 mean my gas cap is bad?

No. The cap isn't part of the vent path. P0446 is about air getting in through the vent, not vapor leaking out. See the GM P0446 guide for the wider GM picture.