P0299 on Buick
Turbo/Supercharger Underboost Condition
P0299 on Buick vehicles indicates turbo/supercharger underboost condition. Au7o has documented this code across 4 Buick models — most commonly on Cascada, Encore, Encore GX. 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. Typical repair costs on Buick range from $450 to $4,000, depending on the specific model and root cause.
Common Causes of P0299
- •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
P0299 on Buick by Model
Buick Cascada(1 issue)
- 1.6L LWC Turbocharger Assembly Failure — Coolant Leak At The Turbo, P0299 Underboost, Cruise Drops Out2016-2019
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.
Buick Encore(1 issue)
- Turbocharger / Oil Supply Line Failure Causing Sudden Loss of Power2013-2018
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.
Buick Encore GX(1 issue)
- Turbocharger Wastegate Actuator Failure Causing "Engine Power Is Reduced" and Underboost (P0299)2020-2025
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.
Buick Envision(1 issue)
- Charge Air Cooler Moisture Intrusion Causing Misfire and Turbo Underboost (2.0T LTG)2016-2020
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.
Looking for P0299 on a different make?
View P0299 across all makes →Frequently Asked Questions
What does P0299 mean on 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 specifically, this code is documented across 4 models.
What causes P0299 on Buick vehicles?▼
Common causes on Buick: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0299 on a Buick?▼
Repair costs on Buick range from $450 to $4,000, depending on the specific model and root cause.
Which Buick models have P0299 documented?▼
Au7o has documented P0299 on 4 Buick models: Cascada, Encore, Encore GX, Envision.