P0299 Code on a Buick: Turbocharger Engine Underboost (Buick Guide)

P0299 on a Buick is "Engine Underboost." The engine computer asked the turbocharger for a certain boost pressure, measured what it actually got, and the actual figure stayed too far below the target for too long. It only applies to turbocharged Buicks — the Encore, Encore GX, Envista, Envision, Regal and Verano turbo models and the newest 2.5T Enclave — and on those vehicles GM has written an unusually large stack of documents about it. The surprise in that stack: GM wrote an entire bulletin because too many turbochargers replaced for P0299 came back with no trouble found. Ice in the charge air cooler, a stuck bypass valve, a restricted vacuum hose and a calibration update all come before the turbo itself.

What Does P0299 Mean on a Buick?

A turbocharged Buick engine has a boost pressure sensor between the turbo and the throttle body. The ECM calculates a desired boost pressure from pedal position, rpm and load, then controls the turbo's wastegate to reach it. P0299 sets when actual boost falls short of desired boost by more than a calibrated limit.

GM's published OBD tables describe two ways it can fail. At steady conditions with boost control active, a positive deviation — desired minus actual — beyond the limit counts as underboost. During transients, if boost rises more slowly than a threshold gradient, that also counts. In GM's 2015 tables (which cover the Encore 1.4T) the code needs two trips to turn on the light; in the 2021 tables that cover the Encore GX engines it is listed as a one-trip code.

P0299 tells you boost was low, not why. Leaks, an open wastegate, intake restriction, ice — or, on one Buick, an over-sensitive calibration — can all set it.

Which Buicks Set P0299

Only turbocharged engines can set it. GM documents name P0299 on these Buicks:

• 2013–2022 Encore, 1.4L turbo (LUJ, LUV and LE2) — the largest group of documents, from wastegate preload to cold-weather icing.
• 2020–2025 Encore GX, 1.2L (LIH) and 1.3L (L3T) three-cylinder turbos — wastegate linkage wear, vacuum supply problems, charge air cooler icing and a calibration update.
• 2024–2025 Envista, 1.2L (LIH/LBP) — wastegate binding and a restricted vacuum hose.
• 2016–2020 Envision 2.0T (LTG) — moisture and ice in the charge air cooler (bulletin 21-NA-074).
• 2021–2023 Envision 2.0T (LSY) — a charge air bypass valve that sticks open.

The 2011–2017 Regal 2.0T, 2013–2016 Verano Turbo, 2016–2019 Cascada 1.6T and the 2025-on Enclave 2.5T can all set P0299 — GM's calibration tables list it for those engines — but we found no GM bulletin naming P0299 on them specifically. Naturally aspirated Buicks (3.6L V6, 2.4L, 2.5L, 3800) have no turbo and cannot set it.

The Encore 1.4T Story

Wastegate preload (2013–2015). GM's PI1366 says P0299 on the 1.4L can come from loss of wastegate preload. Some wear at the actuator rod-to-pin joint is normal and does not set a code; what matters is whether the wastegate lever wiggles freely while the actuator rod stays still. If it does, the preload is insufficient and the bulletin calls for a turbocharger. The later PIP5495N adds that this preload problem is really a 2011–2012 original-actuator issue — the updated actuator has about 5 mm more closing travel, making insufficient preload "very unlikely."

Do not replace the turbo for these (PIP5495N). This is the most useful GM document an Encore owner can show a shop. For 2013–2020 Encore 1.4L, GM lists conditions that do not justify a turbo for P0299: cracks at the wastegate valve port (normal), a broken or oil-clogged wastegate solenoid or hoses, a bent actuator port, a missing actuator clip, a bypass valve with a broken port or water and oil inside, restrictions in the air cleaner, resonator or ducts, collapsed hoses, animal nesting material and excessive exhaust backpressure.

When nothing is found, PIP5495N tells the technician to run GM's Turbocharger Boost Control Test: warm engine, three wide-open-throttle runs to the 1–2 shift, and compare actual against desired boost on a graph. The turbo is replaced only if the difference in the measured window exceeds 14 kPa (2.0 psi).

Cold weather. Bulletin 16-NA-405 (2013–2017 Encore LUV) covers loss of power, smoke and hesitation in the first 10–15 minutes at −18 °C (0 °F) or colder, with P0299, P0236, P2227 or P00C7. The fix was a PCV heater and, depending on version, a front fascia blocker. Bulletin 22-NA-067 (2013–2020 Encore LUV) adds ice in the crankcase vent tube, ice blocking the PCV passage in the cylinder head and sludge at the charge air bypass valve, and its repair can include a new intake manifold. For the 2016–2022 LE2 engine, bulletin 17-NA-221 covers the same cold-weather icing, and PIP5812C describes oil and moisture freezing inside the wastegate regulator solenoid valve — drain it, blow it out at 15–20 psi, and replace it only if the plunger is stuck.

Encore GX and Envista

The 1.2L three-cylinder's wastegate is vacuum-controlled from an engine vacuum pump, and many of its P0299 documents point there.

• 23-NA-058 (2020–2023 Encore GX 1.2L, replacing PIP5829A): cold-start rattle and P0299 from wastegate linkage wear. The rattle test is done on a hoist with a remote start — if touching the wastegate rod with a long screwdriver silences the rattle, linkage wear is present. The earlier PIP5829A adds vacuum tests — about −50 kPa (15 in Hg) at the supply hose at idle — before a turbo is condemned.
• PIP5978 (2020–2024 Encore GX and 2024 Envista 1.2L): the vacuum hose from the pump to the wastegate solenoid can be restricted at its ends by adhesive bonding material. Replace the hose, not the turbo.
• PIP6058A (2024–2025 Envista 1.2L LBP/LIH): P0299 or P0234 from a binding wastegate, confirmed by operating the wastegate by hand with the turbo removed.
• PIP5903 (2022–2023 Encore GX 1.3L L3T): GM's stated cause is "P0299 Improved Diagnostic Sensitivity" — the correction is an ECM reprogram before any other diagnosis.
• 21-NA-293 (2020–2023 Encore GX): charge air cooler icing below −18 °C (0 °F). The fix is a new ECM calibration that changes cold-weather shift patterns so the engine runs higher rpm on the highway.

Envision, Regal and Verano

2016–2020 Envision 2.0T: bulletin 21-NA-074 links P0299, P2227 and P0300 to moisture in the air-to-air charge air cooler. Cold weather freezes it and restricts flow; humid weather lets water collect and get swallowed on the next hard acceleration. GM's repair starts with a smoke test of the cooler, and the bulletin says not to replace the cooler ducts unless they are damaged or leaking.

2021–2023 Envision 2.0T (LSY): PIP5889A says the charge air bypass valve can stick open intermittently. GM tells technicians to inspect it with a borescope rather than remove it, because removing it can free the valve and hide the fault.

Regal and Verano 2.0T: no GM bulletin we found names P0299 on these; their charge air leak bulletin (PIP5402E) names P1101 and P015B instead.

Special Coverages on Buick Turbochargers

• N232395330 — certain 2017–2018 Encore 1.4L (LUV): turbocharger replacement, 10 years or 120,000 miles from the original in-service date. Many of these vehicles may still be inside that window.
• N232407740 / N242450640 / N242484750 — certain 2020, 2021 and 2022 Encore GX 1.2L: turbocharger replacement, 15 years or 150,000 miles. The 2022 coverage is explained in our N242484750 guide.

None of these documents lists P0299 by number — they say only that the check engine light will come on and a code will set, with possible reduced power. A P0299 on one of these VINs is still worth a free dealer coverage check.

Symptoms of P0299

• Check engine light, sometimes on the first occurrence
• Noticeable loss of power, especially merging or climbing
• Reduced engine power message on some models
• Hesitation on acceleration in extreme cold that fades after 10–15 minutes
• Rattle from under the car at cold start (Encore GX wastegate linkage)
• Companion codes: P0234, P0236, P2227, P00C7, P2261

Causes and How to Confirm Each

How Is P0299 Diagnosed?

1. Record every code and the freeze-frame data. Ambient temperature, rpm and boost at the moment it set tell you whether you are looking at an icing event or a hardware fault.
2. Run a VIN check for campaigns and coverages. Ask about calibrations (PIP5903, 21-NA-293), the Encore and Encore GX turbo coverages and the expired cold-weather service updates.
3. Smoke test the charge air path from turbo outlet to throttle body, including the cooler.
4. Inspect the intake side — filter, airbox, ducts and resonator — for restriction or nesting.
5. Check wastegate control. On the Encore 1.4T, the regulator solenoid and its hoses; on the Encore GX and Envista, the vacuum pump, supply hose and solenoid with a vacuum gauge.
6. Check the bypass valve for oil, water or a stuck-open plunger.
7. Graph desired vs actual boost under wide-open throttle. GM's 1.4T threshold for condemning a turbo is a difference above 14 kPa (2 psi).
8. Only then inspect the turbocharger for wastegate preload, linkage wear, binding or wheel damage.

Parts and Cost

Order turbo parts by VIN.

GM Documents That Name P0299 on Buicks

16-NA-405 also refers out-of-warranty vehicles to Special Coverage 17157; we saw that number cited but did not read the coverage itself (corroborated). Have a dealer check your VIN against current bulletins and campaigns rather than relying on any article, including this one.

What Other P0299 Pages Get Wrong

• "P0299 means the turbo is bad." GM wrote a whole PI for the Encore listing turbochargers returned with no trouble found, and the conditions that should not lead to one.
• Ignoring the weather. A P0299 that only appears below 0 °F on short trips is an icing problem with its own GM fixes, not a failed turbo.
• Missing the calibration fix. On a 2022–2023 Encore GX 1.3L, GM's first step is an ECM reprogram.
• Treating the Encore GX like the old Encore. The 1.2L three-cylinder uses a vacuum-operated wastegate; the vacuum pump, hose and solenoid have to be tested first.
• Not checking coverage. 2017–2018 Encore and 2020–2022 Encore GX owners may have turbo coverage measured in years and miles that are still running.

Frequently Asked Questions

Can I drive my Buick with P0299?

Usually the engine still runs, but with less power and sometimes in reduced power mode. Avoid situations where you need full acceleration and get it diagnosed soon — GM notes the cold-weather icing condition can also raise crankcase pressure and cause oil leaks at seals and gaskets.

Does P0299 mean my Encore needs a new turbo?

Not by itself. GM's PIP5495N lists hoses, solenoids, the bypass valve, intake restrictions and icing as things to rule out first, and only condemns the turbo when actual boost misses desired by more than 14 kPa (2 psi) in its test.

Why does P0299 only happen when it's very cold?

Moisture from the air and the crankcase vent can freeze inside the charge air cooler or the wastegate solenoid, restricting boost. GM has cold-weather bulletins for the Encore, Encore GX and Envision describing exactly this.

Is the Encore GX turbo covered?

Certain 2020, 2021 and 2022 Encore GX models with the 1.2L have special coverage for turbocharger replacement at 15 years or 150,000 miles. Coverage depends on the VIN, so ask a Buick dealer to check.

What's the difference between P0299 and P0234?

P0299 is underboost — actual boost below desired. P0234 is overboost — actual above desired. Both point at wastegate control, which is why a frozen solenoid or binding wastegate can set either one.

Will clearing P0299 fix it?

No. The ECM checks boost continuously and the code will return as soon as the condition repeats. Clear it only to confirm a repair.