P0299 means Turbocharger/Supercharger A Underboost Condition. Boost pressure is lower than the computer expects for the current conditions. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0299 means
Modern engines measure boost and fuel rail pressure and compare them with a desired value calculated from engine speed, load and throttle. When actual pressure falls short of desired for long enough, the computer sets a code and often reduces power to protect the engine. Watching desired and actual values side by side on a scan tool shows whether the shortfall is constant or only appears under load.
P0299 symptoms
- Loss of power
- Reduced-power mode
- Whistling or hissing from a boost leak
- Black smoke on diesels
Common causes of P0299
- Boost leak from a loose clamp, split hose or intercooler
- Sticking wastegate, or sticking vanes on a variable geometry turbo
- Failing turbocharger
- Faulty boost pressure sensor
- Restricted air filter or exhaust
How to diagnose P0299
- Pressure-test the intake and intercooler for leaks
- Compare desired and actual boost on a scan tool
- Check wastegate or VGT actuator operation
- Inspect the turbo for shaft play and oil leaks
Can you drive with P0299?
Gently and briefly; the cause can worsen, and a failing turbo can damage the engine. Repair soon.
P0299 tips
On diesels, a split intercooler boot or a loose clamp is the most common cause; listen for a whistle or hiss under load and pressure-test the system. On gasoline turbo engines, a sticking wastegate is another frequent cause, and supercharged engines can set it from a slipping belt or a bypass valve stuck open.
Will P0299 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0299 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0087 | Fuel Rail/System Pressure Too Low |
| P0106 | Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance |
| P0101 | Mass or Volume Air Flow Circuit Range/Performance |
Guides that help
- diesel losing power
- turbo failure symptoms
- variable geometry turbos
- what does an intercooler do?
- vacuum leak
When it is more than a sensor
Our superchargers page lists supercharger kits, and diesel owners can read the 6.7 Cummins turbo guide. If a failed turbo or fuel pump has damaged the engine, compare engines by code on our engines page.
More guides: what does a wastegate do? · 6.7 Cummins turbo actuator.
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