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
Confirm the complaint and exact vehicle criteria first. Inspect the vacuum line and N649 for coolant, then clean and dry suspected leakage, fill the cooling system correctly, inspect at idle and around 2,500 rpm, and pressure-test according to Audi workshop information. If no leak is reproduced, observe the vehicle without replacing parts. If the pump leak is confirmed, replace the failed component and document it. If fresh coolant has entered the vacuum system, inspect the remaining Audi checkpoints and replace only contaminated components; if the downstream checkpoints are clean, replace N649 and clean the line between the pump and N649 as directed by TSB 2070349/5.
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)
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, A6, S3, A7, S7, Q8, A1, RS5.
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.