P0496 Code on a GMC: EVAP Flow During Non-Purge (GMC Guide)

P0496 on a GMC is GM's "EVAP System Flow During Non-Purge." Put simply, the engine computer closed the purge valve and the vent valve, sealing the fuel vapor system — and the fuel tank kept going into vacuum anyway. The only thing that can pull that vacuum is the engine, so GM's diagnostic tables describe P0496 as a test for a purge valve leaking to intake manifold vacuum. On a GMC the code has two notable wrinkles: older Sierras, Yukons and Envoys used a different code, P1441, for the same fault, and on 2016–2017 Acadias GM put the purge valve under a special coverage that lists P0496 first.

What Does P0496 Mean on a GMC?

Fuel vapor from the tank is stored in a charcoal canister. When conditions are right, the ECM opens the purge valve and engine vacuum pulls those vapors into the intake to be burned. When the ECM closes the purge valve, that flow should stop completely.

GM's 2019 table for the Sierra and Yukon engines explains the test: the ECM seals the EVAP system — purge and vent valves closed — and watches tank vacuum, which "should not increase." If it does, there must always be a small amount of purge flow, which means the purge valve isn't sealing. GM adds a useful note: the test detects purge valve leaks to intake manifold vacuum; a purge valve that leaks to the atmosphere is caught by the small-leak test, P0442, instead.

That's why P0496 and P0442 often travel together on a bad purge valve, and why GM's Acadia coverage lists both.

How GM Runs the Test on a GMC

• 2004 truck table (4.3L, 4.8L, 5.3L, 6.0L, 8.1L). GM's "purge valve leak test" fails if tank vacuum reaches 12 inches of water for 2 seconds within about 37.5 seconds (after a 30-second delay) with the purge valve closed and engine vacuum at least 10 kPa. It runs once per cold start, with fuel between 15% and 85% and coolant and intake air between 3.75 °C and 30 °C at start-up. It's a Type B code.
• 2019 Sierra and Yukon table (4.3L, 5.3L, 6.2L). The test fails if tank vacuum exceeds about 2,491 Pa (about 10 inches of water) for 5 seconds with the system sealed. It needs a cold start after at least 28,800 seconds — eight hours — engine off, fuel between 10% and 90%, and start-up intake air between 4 °C and 35 °C. Type B, two trips.

The eight-hour requirement matters. A Sierra that's driven several times a day, but never sits overnight, may not run the test for a while. After a repair, give it a few overnight cold starts before deciding whether it worked.

Which GMCs Set P0496

If you own a 2001 Sierra and see "P0496" on a generic scanner, re-read it with a GM-capable tool; GM's tables for that truck list P1441.

The Acadia Purge Valve Coverage

In September 2019 GM released Special Coverage N192210240 for about 1.17 million U.S. vehicles, including the 2016–2017 GMC Acadia. GM says the purge valve may not fully close, which can make the engine run rough, hesitate or stall at idle, light the check engine lamp and set a code. GM's list of possible codes is P0496, P0442, P0455, P0171 or P0174 — the last two because a leaking purge valve adds unmetered vapor and air, upsetting fuel trim.

For the Acadia the coverage runs 10 years or 150,000 miles from the date the vehicle was first placed in service, whichever comes first. GM lists purge valves 12690512, 55573017, 55567453 and 55569458, chosen by VIN. Since the 2016 models went into service in 2015–2016, most have reached the end of the term; some 2017 Acadias may still be inside it. A dealer VIN check is free and will show whether your Acadia is involved and still eligible.

A related GMC truck coverage: Special Coverage 11304 (January 2012) covered the purge solenoid valve (part 12597567) on 2009 Sierra Hybrid with the 6.0L LFA, for 10 years or 120,000 miles. It named no DTC, and that term has passed for practical purposes.

Turbo GMCs and Purge Pumps

Turbocharged GMCs — the Sierra 1500 2.7L (L3B), the Acadia 2.0L turbo (LSY) and 2.5L turbo (LK0), and the 2023-and-later Canyon (GM lists L2R) — use an EVAP purge pump, because a boosted intake doesn't always have vacuum to pull vapor. GM's bulletin 23-NA-214 covers purge pump replacement and part number interchange for these engines.

GM has put that pump under several 15-year/150,000-mile special coverages that name GMCs: N202324990 (2019–2020 Sierra 1500 2.7L), N232395310 (2020 Acadia 2.0L, 2021 Sierra LD 2.7L), N242441120 (2021 Acadia 2.0L) and N242484740 (2022–2023 Acadia, 2022 Sierra 1500). Those coverages list P1467 and the P146x/P148x family, not P0496. If your turbo GMC has P0496 alongside one of those codes, ask the dealer to check the purge pump coverage for your VIN.

A circuit-code note for the 3.6L: GM's PIP5552 (2018) covers 2017–2018 Acadia 3.6L LGX and Canyon 3.6L LGZ with purge solenoid circuit codes P0459 or P0443 and tells technicians not to replace the purge valve or ECM — clear the codes. Those are circuit codes, not P0496, but they show up on the same valve.

Symptoms of P0496

• Check engine light
• Rough or unstable idle, especially right after a cold start or after refueling
• Hesitation or stalling at idle (named in the Acadia coverage)
• Hard starting after filling the tank, from extra vapor reaching the engine
• Lean codes P0171/P0174 alongside it
• Sometimes no symptom other than the light

Causes and How to Confirm Each

How Is P0496 Diagnosed?

1. Read all codes and check coverages. On a 2016–2017 Acadia, ask for a VIN check against N192210240 before paying for a valve. On turbo models, look for purge pump codes too.
2. Watch tank vacuum with the system sealed. Command the EVAP system closed with the engine running; any rise in tank vacuum points to the purge valve.
3. Test the purge valve directly. Command it off and check for vacuum or flow through it; command it on and confirm it opens.
4. Inspect for charcoal in the purge line. If present, the canister needs attention.
5. Check the vent valve and sensor so you don't replace a good purge valve.
6. Replace the purge valve by VIN, clear the code, and allow several overnight cold starts for the test to run.

Parts and Cost

GM Documents Relevant to P0496 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 P0496 Pages Get Wrong

• Calling it a leak. It's the opposite: too much flow when there should be none.
• "Check the gas cap." A cap can't pull vacuum on the tank. The purge valve can.
• Replacing the canister first. Only if it's shedding charcoal or fails testing.
• Ignoring older GMC codes. Trucks through 2002 used P1441 for this fault.
• Missing the coverage. A 2016–2017 Acadia owner may be paying for a part GM covered.

Frequently Asked Questions

Can I drive with P0496?

Usually, yes. But if the engine idles roughly, hesitates or stalls — symptoms GM names in the Acadia coverage — get it fixed soon, because stalling at idle is a real inconvenience in traffic.

Why is my GMC hard to start after filling up?

A purge valve that doesn't close can let fresh vapor from refueling flood into the intake. That fits P0496.

Is the purge valve on my Acadia covered?

2016–2017 Acadias are in Special Coverage N192210240 for 10 years or 150,000 miles from the in-service date. Many have passed that point, but a dealer VIN check is free.

Why do I have P0496 and P0171 together?

Unmetered vapor and air entering through a leaking purge valve can push fuel trim lean. GM lists P0171 and P0174 alongside P0496 in the Acadia coverage. See the GMC P0171 guide.

Does a turbo Sierra set P0496?

The 2.7L turbo uses a purge pump, and GM's purge pump coverages list P1467 and related codes rather than P0496. If you have both, ask for a coverage check.

How long does P0496 take to come back after a repair?

GM's 2019 Sierra/Yukon test needs a cold start after at least eight hours off, so allow several overnight starts. For the GM-wide picture, see the GM P0496 guide.