P0299 on Buick: How to Diagnose & Fix
Turbo/Supercharger Underboost Condition
4 Buick models · 5 documented issues · 3 critical · $450-$4,000 repair
P0299 on Buick by model: symptoms, diagnosis and fix
On the 1.2L engine, wear in the turbocharger wastegate linkage can cause a rattle on cold start and set code P0299 (engine underboost). When the turbocharger fails, the check-engine light comes on and a message may say the engine power is reduced. Applies to: 2020-2023 Buick Encore GX with the 1.2L LIH engine (bulletin 23-NA-058). GM special coverages N232407740 (2020), N242450640 (2021) and N242484750 (2022) cover turbocharger failure on 1.2L cars; involvement is by VIN. The 1.3L L3T is not listed in these documents.
Common Symptoms
- "Engine Power Is Reduced" message on the driver information center
- Check engine light with sudden loss of acceleration
- Cold-start rattle from the engine compartment
- Vehicle will not exceed roughly 35 mph in limp mode
- Shaking or trembling under load above 35 mph
- Whistling or siren-like noise from the engine bay under boost
- Repeat failure after a prior turbo replacement
How to Fix
Ask a GM dealer to check the VIN for special coverage N232407740 (2020), N242450640 (2021) or N242484750 (2022). Under them, dealers replace the turbocharger as necessary at no charge for 15 years or 150,000 miles, counted from the date the vehicle was first placed in service. Bulletin 23-NA-058 has the technician test the wastegate vacuum supply and the wastegate regulator solenoid valve before removing the turbocharger to check the linkage for wear. In extremely cold weather, bulletin 21-NA-293 lists charge-air-cooler icing as another cause of P0299, corrected by an engine control module reprogram. Outside these coverages, normal warranty rules apply; the bulletins are not a recall or a promise of free repair.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (6)
- GM bulletin 23-NA-058: Cold start rattle, MIL with DTC P0299 (1.2L LIH)tsb
- GM special coverage N232407740: Turbocharger replacement (2020 Encore GX 1.2L)manufacturer
- GM special coverage N242450640: Turbocharger replacement (2021 Encore GX 1.2L)manufacturer
- GM special coverage N242484750: Turbocharger replacement (2022 Encore GX 1.2L)manufacturer
- GM bulletin 21-NA-293: Charge air cooler icing, DTC P0299tsb
- NHTSA owner complaints, 2021 Buick Encore GX (ODI 11619062, 11658466, 11733173)nhtsa
Cascada owners with the 1.6L LWC turbo report the turbocharger assembly itself failing well inside 40,000 miles, distinct from the wastegate-fitting damage GM warned technicians about. Presentation is either an unexplained coolant leak traced to the turbo's water-cooled center section with no warning light, or a P0299 turbo underboost code with weak acceleration and cruise control disengaging as soon as it is set. One 2016 owner was quoted $4,000 at 38,000 miles; another had the turbo replaced under the powertrain warranty in 2020 but the job escalated because a turbo-to-catalytic-converter stud snapped, forcing replacement of the entire catalytic converter assembly.
Common Symptoms
- Coolant loss with no visible leak on the ground
- Check engine light with P0299
- Sluggish acceleration, turbo feels weak
- Cruise control disengages right after being set
- Whining or whistling from the turbo area
How to Fix
Confirm the source first: pressure-test the cooling system and inspect the turbo coolant feed/return lines, then check for boost leaks at the intercooler inlet, throttle-body inlet hose and PCV system before condemning the turbo (a cracked PCV diaphragm is a separate, covered condition). If the turbo center housing is leaking coolant or the compressor/wastegate cannot hold boost, replace the turbocharger assembly; expect the exhaust-side fasteners to be seized and budget for a catalytic converter if a stud breaks. Within 6yr/70k the powertrain warranty covers the turbo. Out of warranty, $2,500-$4,000 at a dealer, less with an aftermarket unit.
Sources for this issue (3)
The 1.4L turbo Encore is known for turbocharger failures that cause a sudden loss of power while driving and a persistent check engine light. NHTSA complaints document dangerous highway events where the vehicle abruptly lost acceleration. GM later issued a field action/warranty extension (Special Coverage N232395330, February 2024) covering turbochargers on 2017-2018 Encores with the 1.4L LUV engine for 10 years / 120,000 miles, with the repair replacing the turbo assembly and associated oil-feed seals and gaskets.
Common Symptoms
- Sudden loss of power on the highway
- Reduced engine power warning
- Check engine light
- Turbo underboost
- Loss of acceleration
How to Fix
Replace the turbocharger assembly along with the turbo oil feed pipe seals, oil return pipe gaskets, exhaust/coolant seals, and related hardware per GM's procedure. For 2017-2018 models with the 1.4L LUV engine, check eligibility for GM Special Coverage N232395330 (10 yr / 120,000 mi from the original in-service date); owners who already paid for a covered turbo replacement can apply for reimbursement. Maintain regular oil changes with the specified oil to protect the turbocharger.
Sources for this issue (1)
Some 1.4L turbo Encores use oil between changes or blow blue smoke, sometimes with a check-engine light and codes P0171, P0300 or P0299. GM's acceptable consumption is 1 quart (0.9 L) in 2,000 miles (3,200 km), not counting leaks. GM lists a leaking camshaft-cover PCV orifice, a missing intake-manifold non-return valve and a weak or broken piston ring land as possible causes. It affects 2013–2019 Encores with the 1.4L turbo LUJ or LUV engine, as listed in GM PIP5197K. GM later replaced the PIP5197 series with bulletin 19-NA-114, which keeps only the PCV-diaphragm test; no GM document found lists the 2020 or 2021 Encore, so this does not cover them. It does not cover Encores with the 1.4L LE2 engine: the 2016–2019 Sport Touring, the LE2 option offered on all but the base model in 2017–2018, and later-build 2021 Encores.
Common Symptoms
- Oil level drops between oil changes
- Blue exhaust smoke
- Check-engine light with code P0171, P0300 or P0299
How to Fix
Check the oil level often and have a GM dealer measure the consumption. Under PIP5197K the technician checks the dipstick and oil-fill cap seals and looks for intake air leaks, then checks the camshaft-cover PCV orifice and replaces the cover if it leaks oil or vacuum. They then measure crankcase pressure at hot idle and on a throttle snap. A normal reading is −11 to −18 inches of water; a reading between −10 and 0 points to cylinder leakage, so the technician does a cylinder leakage test, and only if a broken piston ring land is found are all four piston assemblies replaced. They also check for a missing intake-manifold non-return valve and replace the manifold if it is missing. Normal warranty rules apply; this is not a recall or a promise of free repair.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (2)
The 2.0L LTG turbo's air-to-air charge air cooler collects condensate in its lower core. After long drives in rain or high humidity (heavy fog), a hard throttle application can draw the accumulated water into the engine, causing a sudden multi-cylinder misfire (P0300) and a stumble; in cold weather the moisture can freeze inside the cooler, restricting flow and setting underboost codes P0299/P2227. GM issued TSB 18-NA-020 with a charge air cooler replacement procedure specifically for moisture-related MIL complaints. This affects only the turbocharged LTG cars, not the naturally aspirated 2.5L LCV.
Common Symptoms
- Sudden stumble or misfire on hard acceleration
- Check engine light with random misfire code P0300
- Momentary loss of boost or power
- Worse after long drives in rain or high humidity, or in cold weather
How to Fix
Confirm the misfire pattern is not ignition or injector related, then perform GM TSB 18-NA-020: wipe residual moisture from the boost sensor, smoke-test the charge air cooler, and replace it with the newly designed (wider) part plus the new lower baffle if it leaks or if the vehicle was built on or before January 5, 2019; later builds with no leak go to further diagnosis. Check the intercooler outlet duct for standing water during diagnosis. The bulletin repair is billed under powertrain coverage.
Sources for this issue (2)
P0299 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0299 mean on a Buick?
P0299 stands for "Turbo/Supercharger Underboost Condition." P0299 means the engine computer detected an underboost condition — the turbocharger or supercharger is producing less boost pressure than the PCM expects for the given conditions. The computer compares the manifold/boost pressure sensor reading to a target based on engine load, and when actual boost falls short, it sets this code. The most common real-world cause is a leak somewhere in the intake/charge-air path. You'll typically feel reduced power or sluggish acceleration, and the engine may go into a reduced-power mode. On Buick it is documented across 4 models: Encore GX, Cascada, Encore, Envision.
What are the most common causes of P0299?
The most common causes of P0299 are: Boost/intake leak (cracked or loose charge-air hose or intercooler), Faulty or sticking turbo wastegate or actuator, Stuck or clogged variable-geometry turbo vanes (VGT), Faulty boost pressure or MAP sensor, Leaking or disconnected vacuum/boost control lines, Restricted air intake or clogged air filter, Failed boost control solenoid, Worn or failing turbocharger. The specific cause varies by vehicle.
How much does it cost to fix P0299 on a Buick?
Published repair estimates on Buick range from $450 to $4,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.