P0299 – Turbocharger Underboost (BMW N57)
Fault code P0299 means "Turbocharger Underboost". It is common on N57 (325d–335d, 525d–535d, X5/X6 30d–40d), N47 (118d–123d, 318d–320d, 520d) engines. Below are the real-world causes, step-by-step tests and OEM part numbers.
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P0299 quick summary
| Fault code | P0299 |
|---|---|
| Meaning | Turbocharger Underboost |
| System | Powertrain (Engine & Transmission) |
| Vehicles | BMW |
| Common on | N57 (325d–335d, 525d–535d, X5/X6 30d–40d), N47 (118d–123d, 318d–320d, 520d) |
| Severity | High |
| Can I drive? | Yes, but usually in limp mode with reduced power. Avoid heavy loads until it is repaired. |
| Repair cost | €20 – €3,500 |
Symptoms of P0299
- Loss of power, often at low rpm
- Limp mode and Check Engine light
- Hissing or whistling under load (boost leak)
- Power returns after restarting the engine
- Blue smoke or oil in the intercooler if the turbo bearings are worn
Most common causes of P0299 (most likely first)
Mechanic's Pro Tip
On N57 diesels P0299 is the most common turbo code – and the turbo is usually not the first suspect. Check, in this order: the vacuum actuator diaphragms (a hand pump should hold about 600 mbar), the charge-air hoses and intercooler connections, the vacuum solenoids, and only then the turbo itself. A loose clamp is the cheapest fix you will ever find.
1.Torn diaphragm in a turbo / wastegate vacuum actuator
Most likely2.Charge-air leak at hoses, couplings or intercooler
3.Faulty vacuum solenoid or vacuum cells (often with P0046)
4.Sticking turbo control / actuator position deviation (P2563)
5.Worn turbocharger (excessive shaft play, oil in the intercooler)
Step-by-step diagnostic guide
- 1
Read the DDE fault memory with ISTA or a BMW-capable scanner; note companion codes such as P0046 and P2563.
- 2
Compare specified and actual boost across the rpm range – dips at a specific rpm show which turbo stage is affected on multi-turbo engines.
- 3
Test each vacuum actuator with a hand pump: it must hold about 600 mbar for 30 seconds.
- 4
Pressure-test the charge-air system and inspect hoses, couplings and the intercooler.
- 5
Check the turbo shaft play: more than about 0.20 mm axial or 0.50 mm radial means overhaul or replacement.
Frequently asked questions
Does P0299 mean my BMW turbo is broken?
Usually not. Vacuum actuators, vacuum solenoids and charge-air leaks are more common causes. Check the turbo only after these have been ruled out.
How much does it cost to fix P0299 on a BMW diesel?
A vacuum solenoid costs about 40–80 €, a vacuum actuator 80–150 € fitted. A remanufactured N57 turbo costs about 800–1,500 €, a new one 1,800–3,500 € (the tri-turbo version more).
Related fault codes
- P0401Exhaust Gas Recirculation (EGR) Flow Insufficient
- P2002Diesel Particulate Filter Efficiency Below Threshold (Bank 1)
- 2E81Electric Coolant Pump Fault (BMW Codes 2E81–2E85)
- P0012Intake Camshaft Timing Over-Retarded (Bank 1) – BMW VANOS
- P0016Crankshaft / Camshaft Position Correlation – N47 / N20 Timing Chain
- P0087Fuel Rail/System Pressure Too Low – N47 / N57
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.