P0442 Code on a Buick: EVAP System Small Leak Detected (Buick Guide)

P0442 on a Buick is GM's "EVAP System Small Leak Detected": the engine computer sealed the fuel vapor system, watched it, and saw it lose pressure or vacuum faster than allowed. It is usually not an emergency, but it is the code Buick owners chase longest, because the test only runs under narrow conditions and the leak is tiny. Here is the surprise: every Buick reports its smallest EVAP leak as P0442 — including the German-built Regal and Cascada — so there is no separate "very small leak" code to wait for. GM has also put several Buick-specific documents behind this code, including two purge-valve special coverages, a 2012–2013 LaCrosse/Regal/Verano vent-valve tip and a 2021–2022 Encore canister bulletin.

What Does P0442 Mean on a Buick?

Your fuel tank gives off gasoline vapor all the time. The evaporative emission (EVAP) system stores that vapor in a charcoal canister and later lets the engine draw it in and burn it through a purge valve. A vent valve at the canister lets fresh air in, and a fuel tank pressure sensor tells the engine control module (ECM) what is going on inside.

To check for leaks, the ECM closes the vent valve so the whole system — tank, filler neck, cap, lines and canister — is sealed. GM's own description of the small-leak test, in the 2019 diagnostic tables that cover the Encore, Cascada, Regal, LaCrosse and Enclave, is that it detects a leak of 0.020 inch or larger anywhere between the fuel fill cap and the purge solenoid.

That is a pinhole. A cracked hose end, an O-ring that doesn't quite seal or a cap that isn't clicked down can all do it. GM's diagnostic tip bulletin 21-NA-124 adds the part most owners miss: P0442 can also set from a purge valve or vent valve stuck slightly open, not just from a hole.

For the general GM picture, see our GM EVAP leak codes guide (P0442/P0455).

Which Buicks Set P0442

Essentially all of them. We searched GM's published OBD diagnostic tables from 1997 through 2025, and P0442 appears in the engine groups for every Buick line in that period. What changes is how the test works and what other codes sit beside it.

So if a generic code reader shows P0456 on a Buick, re-read it with a tool that shows GM descriptions. In GM's tables P0456 appears only on supplier engines — Saab, the Opel-built Saturn Astra, the Daewoo Aveo and a few others — never on a Buick.

How a Buick Runs the Small-Leak Test

Knowing the test explains why P0442 can take a week to return — or to prove a repair.

On 2010-and-later Buicks, GM uses engine-off natural vacuum. After you park a warm car, the ECM seals the system and watches tank pressure rise as the fuel heats up, then fall into vacuum as it cools. A sealed system builds and holds both; a leaking one doesn't. GM's 2019 table lists the enable conditions for that Buick group:

• Fuel level between 10% and 90%
• At least 600 seconds of drive time and 5 miles before shut-off
• Coolant at or above about 63 °C
• A test that runs during the hot soak after shut-off, once per trip

GM also averages results over many completed tests before turning the light on or off, so one good day doesn't mean the leak is gone.

Older Buicks did it differently: in the 2002–2003 tables for the 3800, 3.1L and 3.4L engines, the ECM pulled engine vacuum on the sealed system once per cold start and watched it decay.

What GM's Buick Documents Say

GM has published several documents that name P0442 on a Buick. Each one points at a different part, which is why "replace the gas cap" is so often the wrong first move.

2012–2013 LaCrosse, Regal and Verano — a vent valve that only leaks under vacuum (PI0979, May 2013). GM found that on these cars the canister vent solenoid can seal when the system is pressurized but leak when it is under vacuum — and the small-leak test runs under vacuum. A standard smoke machine pressurizes the system to no more than about 13 inches of water, so the leak may never show. GM adds that it may be intermittent, because the seal can rotate each time the valve cycles, and may only appear in cold weather. GM's procedure is to command the vent closed with a scan tool, open the purge valve to pull vacuum, seal the system and watch for vacuum decay; if it leaks down, replace the vent solenoid (GM part 22740537). GM is also explicit: do not replace the EVAP canister unless it fails the leak test.

2021–2022 Encore 1.4L (LE2) — a canister with a bad weld (22-NA-217, January 2023). GM traced P0442 on these Encores to an error in the plastic welding of the canister, which leaves a small leak. The fix is to smoke test the canister and replace it (GM part 42763670) only if it fails. The preliminary version, PIP5862, noted that purge solenoids and purge pumps returned from these vehicles tested with no problem found — so they are not the first part to buy.

2010–2012 LaCrosse and 2011–2012 Regal — corroded rear connector (PIC5327C, May 2012). Corrosion at connector X403 (LaCrosse) or X350 (Regal), behind the right rear wheel well liner, can set P0442 along with vent, tank pressure and fuel level codes. Repair it and pack it with dielectric grease.

Buick Purge Valve Special Coverages

A purge valve that doesn't fully close can set P0442 — and two GM special coverages pay for that valve on specific Buicks.

Special Coverage N192210240 (September 2019) covers the 2016–2017 Encore and Enclave, the 2016 LaCrosse and the 2018 Cascada. GM's condition: the purge valve may not fully close, causing rough running, hesitation or stalling at idle and a check engine light. The codes GM lists are P0496, P0442, P0455, P0171 and P0174. Coverage runs 10 years or 150,000 miles on the Enclave and Cascada and 10 years or 120,000 miles on the Encore and LaCrosse, from the original in-service date. For a 2016 Buick that 10-year window has largely run out; many 2017 Encores and Enclaves and 2018 Cascadas may still be inside it.

Special Coverage N232395300 (June 2023) covers the 2019 Enclave with the 3.6L LFY and the 2020 Encore with the 1.4L LUV, for the same condition and the same code list, for 15 years or 150,000 miles. Those vehicles are well inside the term.

Under both coverages, the dealer follows the normal diagnosis for the code; the purge valve is replaced free only if that diagnosis leads to it. A dealer VIN check is free.

Symptoms of P0442

• Check engine light — often the only symptom
• A faint fuel smell near the rear of the car or the filler door
• Rough idle, hesitation or stalling at idle if a purge valve is stuck partly open (the condition in GM's Buick purge coverages)
• Other EVAP or fuel-level codes alongside it on 2010–2012 LaCrosse and 2011–2012 Regal with connector corrosion

Causes and How to Confirm Each

How Is P0442 Diagnosed on a Buick?

1. Read every code with GM descriptions. P0442 with P0496 or a lean code points toward the purge valve; P0442 with vent or fuel-level codes on a 2010–2012 LaCrosse or 2011–2012 Regal points toward the rear connector.
2. Check your VIN for open coverages and bulletins, especially N192210240 and N232395300 on 2016–2020 Buicks.
3. Reseat the fuel cap and inspect its seal — but don't stop there.
4. Inspect GM's seven connections from 21-NA-124: purge tube at the purge valve, purge tube to chassis line near the transmission, chassis line at the canister, tank load line at the canister, vent valve line, tank load line jumper near the tank, and the fuel cap.
5. Follow GM's order: lines seated, lines undamaged, then the vent valve, then the purge valve.
6. Cycle the purge and vent valves with a bidirectional scan tool while inspecting, as GM recommends.
7. Smoke test under both pressure and vacuum. On a 2012–2013 LaCrosse, Regal or Verano, add GM's purge-and-seal vacuum test from PI0979.
8. Replace only what the test proves — and the canister only if it fails the leak test.
9. Clear the code and let the monitor run: fuel between about a quarter and three-quarters, drives of at least 10 minutes and 5 miles, then park and let the car sit. Expect several days.

Parts and Cost

GM Documents That Name P0442 on a Buick

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

What Other P0442 Pages Get Wrong

• "It's always the gas cap." GM lists the cap as one of seven connections — and its Buick documents point at vent valves, canisters, purge valves and a corroded connector.
• Telling Buick owners to look for P0456. No Buick uses it. The 0.020-inch leak is P0442 on every Buick, even the Opel-built Cascada and Regal.
• Trusting a pressure-only smoke test. GM's 2012–2013 LaCrosse/Regal/Verano tip exists precisely because the vent valve can seal under pressure and leak under vacuum.
• Replacing the canister first. GM's Buick documents say to replace it only when it fails the leak test.

Frequently Asked Questions

Is P0442 serious on a Buick?

Not mechanically urgent. It doesn't usually affect driving, though a purge valve stuck open can cause rough idle or stalling, which GM's Buick coverages describe. It will fail an emissions test, and a light that's already on can hide a new problem.

My Buick scanner says P0456. Is that different?

On a Buick, almost certainly a mismatched description. GM's tables never use P0456 on a Buick engine; the 0.020-inch leak is P0442. Re-read the code with a tool that shows GM descriptions.

Will tightening the gas cap fix P0442?

Sometimes. Reseat it until it clicks and allow several days of normal driving. If the code returns, work through GM's seven connections and the vent and purge valves.

Why can't the shop find the leak on my 2012 LaCrosse or Regal?

GM's PI0979 explains it: the vent solenoid on 2012–2013 LaCrosse, Regal and Verano can leak under vacuum but seal under the light pressure of a smoke machine. GM's purge-and-seal vacuum test is the way to catch it.

Is the purge valve covered on my Encore or Enclave?

Possibly. N192210240 covers 2016–2017 Encore and Enclave, 2016 LaCrosse and 2018 Cascada; N232395300 covers 2019 Enclave (LFY) and 2020 Encore (LUV) for 15 years or 150,000 miles. Coverage depends on diagnosis leading to the valve. A dealer VIN check is free.

How long does P0442 take to clear after a repair?

Usually several days of normal driving with fuel between a quarter and three-quarters and the car parked warm between drives.