Car & driving · Free
P0299: turbocharger or supercharger underboost
P0299 means the turbo did not build the boost pressure the engine computer asked for. Most of the time the reason is outside the turbo: a split boost hose, a loose clamp or a sticking control. Many cars go into limp mode with reduced power.
- No account
- Runs on your device
- Phone & desktop
Check your car for P0299
Runs on your device
Connect your OBD2 adapter
- Plug the adapter into the OBD2 port – usually under the steering wheel, near the pedals.
- Switch the ignition on, or start the engine.
- Bluetooth adapter? Turn Bluetooth on. Nothing else to set up.
This browser cannot talk to OBD adapters. Use Chrome or Edge on Android, Windows or Mac – on iPhone, the free Bluefy browser works with Bluetooth LE adapters. The demo car works everywhere.
Classic Bluetooth adapter (PIN 1234)? Pair it in your system settings first, then choose USB or paired Bluetooth – on a computer or in Chrome 138+ on Android. Wi-Fi adapters cannot work in a browser.
Your car data stays on your device. The page talks to the adapter directly; codes, VIN and values are never uploaded.
Never use it while you drive. Set things up before you set off, or let a passenger handle the phone. Standard OBD2 reads engine and emissions data; ABS, airbag and coding need workshop equipment.
What P0299 means
A turbocharger uses the exhaust gas to compress the intake air, so more air, and with it more fuel, fits into the cylinders. A boost pressure sensor reports the pressure in the intake, and the engine computer controls the turbo with a wastegate or, on most diesels, with adjustable guide vanes.
If the measured boost stays clearly below the target for a while, the computer stores P0299 and usually limits the power to protect the engine. Any leak between turbo and engine, anything that keeps the turbo from spinning up and any fault in its control can cause it.
Symptoms of P0299
- Noticeably less power, often with limp mode.
- A hissing or whistling sound under load: escaping boost.
- Black smoke on diesels.
- Higher fuel consumption.
Causes of P0299, cheapest first
Work down the list in order: the first checks cost little or nothing, the last ones are jobs for a workshop.
A leaking boost hose or intercooler
Hoses crack, clamps work loose and intercoolers get hit by stones. Look for oily patches on hoses and joints, and listen for hissing under load.
A blocked air filter or intake
A clogged filter starves the turbo. It is the cheapest thing to check.
A boost control problem
A vacuum hose to the wastegate or vane actuator, a faulty boost control solenoid or a sticking actuator rod keeps the turbo from building pressure.
Sticking guide vanes (diesel)
Soot can jam the variable vanes of a diesel turbo, especially on cars driven mostly in town. A long drive under load sometimes frees them; otherwise they need cleaning.
A blocked exhaust or particulate filter
A clogged diesel particulate filter or catalytic converter holds back the exhaust gas that drives the turbo.
A worn turbo
Shaft play, oil leaks and a siren-like noise mean the turbo itself is worn. It is the most expensive cause, so rule out the others first.
Can you drive with P0299?
Drive gently to a workshop. Limp mode protects the engine, but with reduced power, overtaking and joining a motorway become risky. Drive gently and have it checked soon. If you see blue smoke or hear a loud whine or grinding from the turbo, stop to avoid engine damage.
Check P0299 with OBD Studio
Connect your adapter above, or try the demo car, then:
- In Live data, graph Intake manifold pressure and Barometric pressure under load, with a passenger handling the phone. Boost is the difference between the two.
- Boost that rises slowly or stops at a low value points to a leak or a control problem; compare it with what is normal for your engine.
- The freeze frame in Fault codes shows engine speed and load at the moment of the fault.
- In Inspection, the Boost pressure monitor and, on cars with CAN, the boost result under Read self-tests show the car’s own checks.
More fault code guides
Each of these codes has its own page with causes ranked by cost and the checks that go with them.
- P0420Catalyst efficiency below threshold
- P0171System too lean
- P0300Random or multiple misfire
- P0455EVAP system large leak
- P0442EVAP system small leak
- P0128Engine warms up too slowly
- P0172System too rich
- P0401EGR flow too low
- P0101Air flow sensor implausible
- P0135Front O2 sensor heater
- P0016Crankshaft and camshaft out of step
- P0011Intake camshaft timing over-advanced
- P0141Rear O2 sensor heater
- P0113Intake air temperature sensor high
- P0457Fuel cap loose or missing
- P0700Transmission control system fault
- P0087Fuel rail pressure too low
- P0562System voltage low
- U0100Lost communication with engine computer
More OBD Studio pages
Frequently asked questions
Can I drive with P0299?
Usually yes, but with less power. Drive gently and have it checked soon. Stop if the turbo makes loud noises or the engine smokes heavily, because a failing turbo can damage the engine.
Does P0299 mean my turbo is broken?
Not necessarily. Leaking boost hoses, loose clamps, sticking controls or a blocked filter cause many P0299 codes. The turbo itself is the last thing to replace.
Why does P0299 appear only on long uphill drives?
Under sustained load, a small leak or a weak actuator has the most effect. The car then misses its boost target long enough to set the code.
Can I read P0299 without going to a workshop?
Yes. With any ELM327-compatible Bluetooth LE or USB adapter, OBD Studio on this page reads P0299 and every other stored code for free, shows the freeze frame and clears the code after the repair. Nothing to install, no account.
