P0299 on Buick: How to Diagnose & Fix
Turbo/Supercharger Underboost Condition
4 Buick models · 4 documented issues · 3 critical · $450-$4,000 repair
P0299 on Buick by model: symptoms, diagnosis and fix
The 2.0L LTG turbo's air-to-air charge air cooler collects condensate in its lower core. Under humid conditions or after short trips the accumulated water is slugged into the intake on a hard throttle application, causing a sudden multi-cylinder misfire, a stumble, and in some cases an underboost/turbocharger performance code. 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 shudder or stumble under acceleration
- Check engine light with random misfire codes
- Momentary loss of boost/power
- Symptom worse in humid weather or after short cold trips
How to Fix
Confirm the misfire pattern is not ignition or injector related, then perform GM TSB 18-NA-020: replace the charge air cooler with the updated part and clear codes. Reprogram the ECM to the latest calibration at the same time, and check the intercooler outlet duct for standing water during diagnosis.
Sources for this issue (2)
The 1.4L turbo Encore is known for turbocharger failures, often tied to the turbo oil feed/supply line, 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 covering 2017-2018 Encore turbochargers 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, check eligibility for the GM turbocharger warranty extension (10 yr / 120,000 mi). Maintain strict oil change intervals to avoid oil-feed line coking that accelerates turbo failure.
Sources for this issue (1)
Owners of 2016-2018 Cascadas 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. Dealers have advised owners with P0299 to replace the turbo outright after ruling out cheaper causes.
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 single-scroll turbocharger used on both the 1.2L LIH and 1.3L L3T three-cylinder engines suffers wastegate actuator and internal turbo failures. The electric wastegate actuator loses calibration or the linkage binds from heat cycling and carbon, so the ECM can no longer hold commanded boost. The module sets an underboost fault, drops the vehicle into a reduced-power limp mode, and in the worst cases the turbo center section itself fails. NHTSA complaints on the Encore GX and its platform twin (Chevrolet Trailblazer) repeatedly describe the failure recurring after a first turbo replacement, indicating the replacement part shares the same weakness. Owners commonly report it first appearing under highway load or when merging.
Common Symptoms
- "Engine Power Is Reduced" message on the driver information center
- Check engine light with sudden loss of acceleration
- 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
Scan for P0299 and check actual vs. commanded boost with a scan tool before parts are thrown at it. Inspect the charge-air piping and intercooler couplers for split boots and the PCV/oil separator for excessive crankcase pressure, which drives oil into the turbo. If the wastegate actuator is out of calibration, GM's remedy is actuator/turbo assembly replacement and a relearn; a leaking or shaft-play turbo requires the full turbocharger assembly. Address any charge-pipe leak first, since a boost leak throws the same code far more cheaply.
Sources for this issue (3)
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: Envision, Encore, Cascada, Encore GX.
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.
Looking for P0299 on a different make?
View P0299 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.