P0299 on Audi: How to Diagnose & Fix
Turbo/Supercharger Underboost Condition
11 Audi models · 13 documented issues · 8 critical · $200-$9,000 repair
P0299 on Audi by model: symptoms, diagnosis and fix
The BorgWarner BV43 variable-geometry turbocharger (OEM part 03L253056, BorgWarner 53039880208) can fail due to oil starvation, bearing wear, or variable geometry vane sticking/seizing. The most common failure mode is the variable vanes sticking or seizing, causing overboost or underboost. Catastrophic failures (compressor shaft snapping) are less common but documented. Failures typically occur around 100,000-150,000 miles.
Common Symptoms
- Loss of power
- Excessive black smoke
- Turbo whine or grinding
- Check engine light with boost codes
- Oil in intercooler
- Overboost shutdown (limp mode)
- Turbo actuator fault codes
How to Fix
Regular oil changes with VW 507.00 spec diesel oil are critical - the turbo depends on clean oil for bearing lubrication. Replace turbo if failed using OEM BorgWarner unit (03L253056). Always replace the turbo oil feed line (03L145771) and oil return line (03G145736F) with new gaskets (03L145757Q oil return gasket) when replacing the turbo. Let engine idle 30-60 seconds before shutdown to allow turbo to cool down.
Sources for this issue (1)
The SQ5 3.0T supercharged V6 shares supercharger nose bearing issues with the S4/S5. The intercooler water pump also fails, causing heat soak and reduced performance, especially in warmer climates.
Common Symptoms
- Whining from supercharger
- Reduced boost
- Heat soak power loss
- Supercharger belt squeal
- Intercooler pump code
- Elevated intake temps
How to Fix
Replace supercharger nose bearing kit. Replace intercooler pump if failing. Service supercharger belt tension.
Sources for this issue (1)
Audi identifies coolant loss from the mechanical coolant pump on 2018-2024 SQ5 V6 TFSI models. In some cases P0299 is logged when coolant entering the vacuum system impairs changeover valve N649. Audi cautions that a small trace on the pump drip cup can be normal and that dried deposits at the vacuum connection alone do not confirm a leak. This evidence does not establish an inherent design defect, a fixed failure mileage or a "when, not if" failure.
Common Symptoms
- Coolant loss or visible coolant leak
- Coolant warning lamp
- Engine warning lamp
- P0299 underboost in some cases
How to Fix
For an applicable vehicle, follow Audi TSB 2070349/4 and current workshop information. Locate the leak precisely: clean and dry the area, fill the cooling system, check for leakage at idle and up to about 2,500 rpm, and test the cooling system as the workshop manual specifies. If no further leak is found, Audi says to keep observing without replacing parts; if the leak returns, replace the leaking component. Where P0299 is logged, the bulletin attributes it to switch valve N649 contaminated with coolant from a leaking pump, so have that secondary damage assessed.
Sources for this issue (1)
The S8 4.0T V8 shares coolant line issues with other 4.0T Audi models but the heavier sedan and higher power tune accelerate wear. Turbo oil and coolant line failures can cause expensive damage if not caught early.
Common Symptoms
- Coolant loss
- Turbo oil leak smell
- Overheating warning
- White exhaust smoke
- Low coolant light
- Oil in coolant or coolant in oil
How to Fix
Replace all turbo coolant and oil feed lines preventatively at 60,000 miles. Monitor coolant levels closely.
Sources for this issue (2)
The water-to-air intercooler system on the S5 3.0T uses an electric coolant pump that can fail, causing elevated charge air temperatures and reduced power. Heat soak becomes severe in warm climates.
Common Symptoms
- Heat soak power loss
- Reduced boost performance
- Intercooler pump fault code
- Elevated intake temps
- Sluggish acceleration in heat
- Check engine light
How to Fix
Replace intercooler coolant pump. Check intercooler lines for leaks and flush the circuit during replacement.
Sources for this issue (1)
The S7 with the 3.0T supercharged V6 (2012-2018) uses an electromagnetic clutch to engage the supercharger. Over time, the clutch disc wears out or the torsional isolator (damper) fails, creating a loud rattling, grinding, or "bag of marbles" sound from the front of the engine. This is most noticeable on cold starts or under load. A failed clutch prevents the supercharger from engaging, causing significant power loss. A failed isolator damages internal supercharger components, requiring complete supercharger replacement. Oil contamination accelerates wear—if oil becomes contaminated with dirt or debris, it causes premature failure of internal components. AudiWorld forums report failures between 60,000-120,000 miles, with repair costs of $1,500-$5,000.
Common Symptoms
- Loud rattling, grinding, or "marbles" noise from front of engine
- Noise most noticeable on cold start or light throttle
- Significant power loss (feels like naturally aspirated V6)
- Check engine light with underboost codes (P0234, P0299)
- Supercharger whine disappears (clutch not engaging)
- Belt squeal from supercharger pulley
- Metal debris in oil (severe internal damage)
How to Fix
If caught EARLY (noise but no power loss): Replace supercharger clutch ($1,500-$2,500 with labor). Clutch can be replaced without removing supercharger. If SEVERE (grinding + power loss): Replace complete supercharger assembly ($3,500-$5,000 installed). PREVENTION: Service supercharger oil every 40,000 miles despite Audi saying "lifetime." Change engine oil every 5,000 miles with high-quality synthetic. Avoid aggressive launches—gentle driving extends clutch life. Budget for this repair if buying a used S7.
Sources for this issue (1)
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 Audi?
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 Audi it is documented across 11 models: A3, SQ5, S8, S5, A7, S7, S3, Q8, RS5, A1, A6.
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 Audi?
Published repair estimates on Audi range from $200 to $9,000 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.