P0299 on Cadillac: How to Diagnose & Fix
Turbo/Supercharger Underboost Condition
2 Cadillac models · 2 documented issues · 1 critical · $200-$6,500 repair
P0299 on Cadillac by model: symptoms, diagnosis and fix
The XT4 uses the 2.0T LSY engine which is an evolution of the LTG found in the ATS/CTS. The LSY has improved reliability but shares some issues including PCV system problems and turbo coolant line leaks. The turbo coolant lines can develop leaks at the connections, causing coolant loss and potential turbo damage from overheating. The PCV valve/cover can fail causing oil consumption. These issues typically appear between 40,000-80,000 miles.
Common Symptoms
- Coolant level dropping slowly
- Sweet smell from engine bay (coolant leak)
- Check engine light with misfire or lean codes
- Excessive oil consumption
- Turbo whistle changes or louder than normal
How to Fix
Inspect turbo coolant lines and connections for leaks - replace lines if seeping. PCV system is integrated into valve cover - replace valve cover assembly if PCV fails. GM has released updated coolant line designs for some affected vehicles. Regular maintenance with full synthetic oil at 5,000-mile intervals is important for turbo health.
Sources for this issue (1)
GM issued Service Update 17408 covering 2016-2018 Cadillac CT6 sedans built with the 3.0L V6 twin-turbo (RPO LGW) after turbochargers were found capable of shedding turbine-wheel material. Owners report a whistle, siren or grinding noise from the turbo area followed by a hard loss of boost and a check-engine light. Because the LGW runs two small turbos, a single failed unit can drop the car into reduced power while the other side still spools, which is why the complaint is usually described as 'sudden loss of power under acceleration' rather than a no-start. Metal debris from a disintegrating turbine wheel can be drawn downstream, which is what turns a turbo replacement into an engine replacement in the worst cases. This is specific to the LGW twin-turbo — the 2.0L four and the naturally aspirated 3.6L LGX in the same body do not share it.
Common Symptoms
- Whistling, siren or grinding noise from turbocharger area
- Sudden loss of boost and reduced engine power
- Check engine light
- Blue smoke on acceleration
- Metal debris found in charge piping
How to Fix
Check VIN eligibility and complete GM Service Update 17408 before buying a turbocharger. The service information requires diagnosis and, during the covered period, controlled dealer parts ordering; left/right turbo and calibration branches cannot be represented by one safe retail link.
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 Cadillac?
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 Cadillac it is documented across 2 models: XT4, CT6.
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 Cadillac?
Published repair estimates on Cadillac range from $200 to $6,500 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.