Understanding the system and symptoms
Reduced boost can arise from charge-air leakage, wastegate control faults, diverter valves, sensors, exhaust restrictions or damaged turbocharger hardware. The turbocharger itself is only one candidate.
How a technician narrows down the cause
Compare specified and actual boost under controlled conditions, then pressure-test charge-air plumbing and inspect clamps and intercooler connections. Verify actuator movement and command with the correct engine-specific procedure. Check pressure sensor plausibility before attributing underboost to a turbocharger.
Model-specific context: Audi A5; researched applications 2010–2018; platform A5 B8, A5 B9 Coupe. Exact applicability should be checked against the vehicle identification number and equipment.
What owners may notice in researched cases
- MIL with P0299 and lack of boost
- P0299 underboost
- MIL, lack of power and P0299
Diagnostic observations from the source cases
The available technical cases describe checks such as Source-documented diagnostic sequence; Command turbocharger wastegate with scan tool; Inspect wastegate linkage and pivots. These checks help distinguish competing causes before recommending replacement.
Possible causes identified in individual cases
The underlying causes documented in individual cases included Loose wastegate linkage; Damaged turbocharger wastegate flapper; Damaged wastegate linkage; Open-circuit turbocharger recirculating valve N249. These are examples of verified findings in those cases, not a prediction of what has failed on every Audi A5.
Repairs reported in the source cases
Repairs reported to resolve documented cases included Repaired loose wastegate linkage per TSB 21-14-18; Replaced turbocharger assembly; Replaced wastegate linkage; verified no codes returned; Replaced N249 turbocharger recirculating valve; verified strong performance and no returning DTC. A repair that succeeded on one vehicle should only be recommended for another after confirming the same fault.
Fault codes recorded in the research
Codes mentioned in the research: P0299, P2563, 09571. Codes can have different interpretations depending on model and conditions.
Verification and next steps
Confirm the requested boost is achieved without overboost or underboost faults, and inspect for oil or exhaust leaks after any turbo-related repair.
If your Audi A5 is showing these symptoms, Mich’s Foreign Cars in Hickory, NC can discuss an appropriate diagnostic appointment. Call 828-324-6012 and provide the year, engine, warning messages and any available fault codes.