CASE 005
P0299 Turbo Underboost
advanced
25 min
Diesel
Vehicle
- ModelTraining MPV 2.0
- Engine2.0 TDI
- Mileage168,000 km
Customer complaint
Loss of power, especially on hills. The turbo seems quiet and acceleration is flat.
History
Turbocharger replaced 10,000 km ago. The symptom is slowly returning.
Fault codes
P0299 Turbocharger/supercharger underboost
Live data
- Boost pressure actual vs requestedActual clearly below requested
- MAF reading under loadLower than expected
Measurements
- Visual inspection of boost hosesOil mist around a hose joint
- Charge pipe pressure testAudible leak
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Diagnostic case
Next step — Reasoning.
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Confirmed cause
Boost leak in the charge-air system (split or loose hose), not a failed turbocharger.
Reasoning
Actual boost below requested, with oil mist and an audible leak under pressure, identifies a leak rather than a turbo fault. A new turbo cannot overcome a leak, which explains why the symptom returned.
Recommended repair
- Replace the split charge hose and secure the joints.
- Re-test boost pressure against requested values.
- Clear the code and road test under load.
Related tools
Related OBD codes
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.