P0455 Code on a GMC: EVAP System Large Leak Detected (GMC Guide)

P0455 on a GMC is GM's "EVAP System Large Leak Detected." The name sounds like a hole you could put a finger in, and sometimes it is — a gas cap left off, a line that popped loose. But GM's own definition says the test detects "a weak vacuum condition (large leak or purge blockage)." In other words, a purge valve stuck closed can set the same code as a missing cap, and on Sierra and Yukon trucks GM has three bulletins where a dust- or water-contaminated vent valve sets P0455 along with P0442, P0446 and P0449. Older GMC trucks are a further twist: through the 2002 model year they didn't use P0455 at all.

What Does P0455 Mean on a GMC?

Your GMC stores fuel vapor in a charcoal canister. While you drive, the engine computer opens the purge valve so intake vacuum pulls those vapors into the engine. For the large-leak test, it also closes the canister vent solenoid at the canister. With the vent shut, purge flow should pull a measurable vacuum on the fuel tank. If enough purge flow passes and the tank never reaches the expected vacuum, the system either has a big opening — or vacuum isn't reaching it at all.

That is why GM's 2021 bulletin 21-NA-124 lists four causes for P0455: an unseated tube connection, a damaged tube, a canister vent valve stuck open, or a purge valve stuck closed. Only two of those are "leaks" in the everyday sense.

Which GMCs Set P0455

All gas-engine GMCs from the 2003–2004 model years on use P0455: Sierra and Sierra HD gas trucks, Yukon and Yukon XL, Savana, Canyon, Envoy, Acadia and Terrain. Duramax diesels don't have this system. Model year matters for older trucks:

So if you have a 2001 Sierra and read about P0455, the closest match in your truck's computer is P0440. If your 2001 shows P0455, re-read it with a GM-capable tool.

How the Large-Leak Test Works on a GMC

Unlike the small-leak test, which runs with the engine off, the large-leak test runs while you drive.

• 2004 truck table (4.3L, 4.8L, 5.3L, 6.0L, 8.1L). GM calls it the "weak vacuum test." It runs on a cold start — coolant and intake air both between 3.75 °C and 30 °C at start-up — with fuel between 15% and 85%. If tank vacuum stays below 11 inches of water for roughly 30–80 seconds of purge (depending on application), it fails.
• 2019 Sierra and Yukon table (4.3L, 5.3L, 6.2L). The ECM closes the vent valve, purges, and counts how much purge flow has passed. If more than 9 liters of purge volume goes through before tank vacuum reaches about 2,740 Pa (around 11 inches of water), it records a large leak. Fuel must be between 10% and 90%, and the test runs once per cold start.

GM's 2019 table has a detail every GMC owner should know. On trucks with a fuel cap, if the first P0455 failure came right after a refueling event, the light turns off after the first passing test — GM treats it as a cap left loose. Otherwise, the light goes off only after three consecutive passes. On capless systems it is always three. A "weak vacuum follow-up test" — GM also calls it the fuel cap replacement test — can run after a failure or on a hot restart to let a repaired system pass sooner.

GMC Truck and Van Bulletins

These verified GM documents name P0455 on GMC trucks and vans:

• 15-06-04-002 (April 2015) — 2011–2015 Sierra, including 2500/3500. Dirt, dust or water in the vent's fresh-air path can restrict flow or corrode the CVS valve; the code list is P0442, P0446, P0455 or P0449, and the tank may be hard to fill. GM installs a revised sealed CVS valve with a remote pre-filter (filter kit 23103351) and says not to replace the canister unless it fails a leak test or is contaminated.
• 09-06-04-028D (April 2014) — 2007–2010 Yukon and Yukon XL 1500, hybrids included. Moisture and corrosion at the CVS valve; revised vent assembly 20995472 and jumper harness 19257603.
• 23-NA-073 (March 2025) — 2019–2025 Sierra 1500 and 2020–2025 Sierra HD. Dust can plug the canister and vent solenoid; GM's fix is a customer-pay in-line filter (86792068, 86792069).
• 15-NA-019 (December 2015) — fuel odor during filling or at idle with possible P0442 or P0455 on 2013 Sierra light duty and 2014–2015 Sierra 1500 (not regular cab) and 2013–2014 Yukon 1500 models. A fractured filler neck recirculation line connector is the cause; GM lists replacement vent hoses by model.
• PI0873 (December 2012) — 2012–2013 Savana 3500–4500 cutaways with an upfitter body and side-mounted tank. The fuel cap tether can bind or get caught under the cap seal, so the cap never seals; P0442 and/or P0455 set. GM relocates the tether and directs the claim to the upfitter.

Why would a vent valve set a "leak" code? A vent valve that doesn't close fully lets outside air in during the test, so tank vacuum never builds — exactly what GM's 21-NA-124 lists as a stuck-open vent valve. The truck bulletins list leak codes and the vent restriction code P0446 together because the same contaminated valve can fail either way.

Acadia, Terrain and Envoy Notes

• 2016–2017 Acadia — Special Coverage N192210240 covers a purge valve that may not fully close. GM lists P0455 among the possible codes, with P0496, P0442, P0171 and P0174, plus rough running or stalling at idle. Coverage for Acadia is 10 years or 150,000 miles from the in-service date, so many have reached or are nearing the end of it.
• 2019 Acadia and Terrain — GM's PIE0528 engineering request lists P0455 with P0442, P0446, P0449 and P0498 for canisters leaking at the vent-solenoid O-ring or the fresh-air filter box. It applies only if the PIE shows in the VIN's warranty history.
• 2002–2004 Envoy — NHTSA's index lists GM bulletin 05-06-04-014 with diagnostic aids for P0440, P0455 and P0442 on the Envoy and Envoy XL. We could only read the summary, so it is corroborated.

Symptoms of P0455

• Check engine light, often right after a fill-up
• "Check fuel cap" or similar message on some models
• Strong fuel smell, especially near the filler or rear of the truck
• Hard to fill or nozzle clicking off early (contaminated vent path)
• Rough idle or stalling — only when a purge valve stuck open is also involved, as on the Acadia coverage
• Failed emissions inspection

Causes and How to Confirm Each

How Is P0455 Diagnosed?

1. Read all codes. P0455 with P0446 or P0449 on a Sierra or Yukon points toward the vent valve.
2. Check the cap and filler. Ask whether the light came on right after fueling.
3. Inspect GM's seven connections listed in 21-NA-124: purge tube at the intake, purge tube to chassis line near the transmission, chassis line and tank line at the canister, the vent valve line, the tank load-line jumper and the fuel cap.
4. Test the vent valve. Command it closed and open with a bidirectional scan tool; on trucks inspect the valve and pre-filter for contamination.
5. Test the purge valve. Command purge and watch for tank vacuum. No vacuum with a sealed system means a purge blockage.
6. Smoke test under both pressure and vacuum. GM notes some leaks show only one way.
7. Repair and verify. Clear the code and let the test run on a cold start with fuel between a quarter and three-quarters.

Parts and Cost

GM Documents Relevant to P0455 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 P0455 Pages Get Wrong

• "Large leak means a big hole." GM's definition includes a purge blockage — no hole at all.
• "Just tighten the cap." Sometimes right, but GM lists six other connections and two valves.
• Ignoring model year. GMC trucks used P0440 for this fault through 2002.
• Replacing the canister first. GM's truck bulletins say not to without a failed test or contamination.
• Expecting the light to go off at once. Unless the failure followed a fill-up, GM wants three passing tests.

Frequently Asked Questions

I just filled up and got P0455. What now?

Check that the cap is on and clicked, then drive normally. On capped GMC trucks, GM's logic turns the light off after the first passing test if the failure followed a refueling event.

Is P0455 serious?

It won't hurt the engine by itself, but raw fuel vapor is escaping and you'll fail an emissions test. If you smell fuel strongly, have it checked promptly.

Why does my Sierra have P0455 and P0446 together?

That combination is what GM describes in its Sierra and Yukon vent valve bulletins — dust or water in the vent valve and its fresh-air path.

Can a bad purge valve cause P0455?

Yes. GM says a purge valve stuck closed sets P0455, because purge vacuum never reaches the tank.

Does P0455 apply to my 2000 Sierra?

GM's 1998–2002 truck tables use P0440 for the same large-leak fault. Confirm what your truck actually stored with a GM-capable scanner.

How is P0455 different from P0442?

P0442 is the 0.020-inch small leak found during the engine-off test; P0455 is a weak-vacuum result during driving. Our GMC P0442 guide covers the small leak, and the GM EVAP leak codes guide covers both.