P0299: Turbocharger/Supercharger "A" Underboost Condition
The boost pressure is lower than the engine control unit expects.
Normal risk
Usually drivable with reduced power. Have it checked soon.
Short answer · Can I keep driving with P0299?
Usually yes, with less power. Have it checked soon, because a boost leak or sticking turbo can get worse. If you hear grinding or see blue smoke, stop and have it checked.
What does P0299 mean?
Code P0299 means the turbo or supercharger does not produce the expected pressure. Common causes are a split intake hose, a sticking wastegate or vanes, or a faulty boost control.
Diesels with variable vane turbos used mainly for short trips are especially prone to sticking vanes.
What the car does when the code is set
The check engine light comes on and the car has noticeably less power, especially when accelerating or climbing. Some engines go into limp mode. You may hear a whistle or hiss from a boost leak or see black smoke on diesels.
How the system works
A turbocharger or supercharger raises the pressure in the intake so the engine can burn more fuel and produce more power. The engine control unit sets a target boost pressure for each load point, moves the wastegate or variable vanes to reach it, and measures the real pressure with a sensor in the intake. If the measured boost stays below the target for longer than allowed, it stores an underboost code. The cause can be anything that loses pressure on the way or prevents the turbo from building it.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Boost leakA split intercooler hose, loose clamp or leaking intercooler.
- Sticking wastegate or vanesSoot can make variable vanes stick, especially on diesels used for short trips.
- Faulty boost control solenoid or hosesThe actuator does not receive the right control signal.
- Worn turbochargerShaft play or damaged blades.
- Restricted intake or exhaustA blocked air filter, particulate filter or catalytic converter.
How it is diagnosed
- Inspect intake hoses and intercoolerLook for oil-wet joints, splits and loose clamps. A boost leak test pressurises the intake to find leaks.
- Check the actuatorMake sure the wastegate or vane actuator moves freely and follows the commands.
- Compare desired and actual boostWatch live data during a test drive with full load in a safe place.
- Check the turboWith the engine off, check the shaft for play and the blades for damage.
Questions about P0299
Does a whistling noise mean a boost leak?
Often, yes. A new whistling or hissing under acceleration is typical for a split hose or loose clamp on the pressure side.
Can a clogged particulate filter cause underboost?
Yes. Exhaust back-pressure reduces turbo efficiency. Check the particulate filter status if both codes are present.