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P0299Turbocharger/Supercharger "A" Underboost Condition

What it means

Actual boost pressure stays clearly below the requested value under load. Usually boost air is escaping, or the turbo control can't build pressure.

Symptoms

  • No power above about 2,000 rpm
  • Hissing or whistling under acceleration
  • Limp mode, sometimes black smoke

Common causes

  • Split or detached boost hose / leaking intercooler
  • Sticking variable vanes or wastegate stuck open
  • Faulty boost control solenoid or vacuum leak to the actuator
  • Worn turbocharger or restricted exhaust (blocked DPF)

What to check first

  1. Compare requested and actual boost under load (at idle they are normally equal)
  2. Smoke-test the pressure side between turbo and engine
  3. Check actuator movement and the vacuum supply
Can I drive with P0299? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.
Practise it: Split intercooler hose (diesel) in the engine simulator shows this fault in live data, tests and on the scope.Open in the simulator

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

How to test the parts behind P0299

MAP and boost pressure sensorWiring, typical values, multimeter and scope testsTurbo actuator (variable geometry)Wiring, typical values, multimeter and scope tests

Known engine problems that set P0299

1.9 TDI PD: Sticking turbo vanes and limp modeVolkswagen, Audi, Skoda, Seat, Ford · typically 120,000–250,000 km1.5 dCi K9K: Turbo failure from oil starvationRenault, Dacia, Nissan, Mercedes-Benz, Suzuki · typically 120,000–220,000 km1.6 HDi/TDCi DV6: Turbo failure from a blocked oil feedPeugeot, Citroën, Ford, Volvo, Mazda, Mini · typically 100,000–220,000 kmMercedes OM651: Split charge-air hoses and limp modeMercedes-Benz · typically 100,000–250,000 km1.2/1.4 TSI EA111: Turbo wastegate rattle (1.4 TSI 122–125 hp)Volkswagen, Audi, Skoda, Seat · typically 80,000–180,000 km

Cases with P0299 (2)

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Limp mode when loaded on hills, whoosh under boostTraining case · 2013 Mercedes-Benz Sprinter 316 CDI · 2.1 CDI (OM651) · fixed: Charge-air hose split on the inside of a bend, softened by oil vapour.Siren noise under boost, blue smoke and loss of powerTraining case · 2009 Peugeot 308 · 1.6 HDi 110 (9HZ) · fixed: Turbo bearings failed from oil starvation: carbon from a leaking injector washer

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P0299: questions and answers

What does P0299 mean?

P0299: Turbocharger/Supercharger "A" Underboost Condition. Actual boost pressure stays clearly below the requested value under load. Usually boost air is escaping, or the turbo control can't build pressure.

What are the symptoms of P0299?

No power above about 2,000 rpm. Hissing or whistling under acceleration. Limp mode, sometimes black smoke.

What causes P0299?

Split or detached boost hose / leaking intercooler. Sticking variable vanes or wastegate stuck open. Faulty boost control solenoid or vacuum leak to the actuator. Worn turbocharger or restricted exhaust (blocked DPF).

How do you diagnose P0299?

1. Compare requested and actual boost under load (at idle they are normally equal) 2. Smoke-test the pressure side between turbo and engine 3. Check actuator movement and the vacuum supply

Can I drive with P0299?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.