This code usually needs a check soon to find out what is wrong.
Trouble codes · P0299
P0299 meaning
Turbocharger/Supercharger A Underboost Condition
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Loose or split boost hose
- Boost control valve or actuator fault
- Worn turbocharger or restricted intake or exhaust
What you can check
With the engine off and cold, look from above for a loose charge-air hose or oily marks around a split. Describe when power drops; have boost control tested before replacing the turbo.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Turbocharger
- A device that pushes extra air into the engine. Pressure, speed and vane readings help explain a loss of power.
- Intake air pressure (MAP)
- MAP measures air pressure inside the engine's intake; barometric pressure measures the outside air. They help the computer work out engine load and the right fuel amount.
- Engine load
- How hard the engine is working, rather than how fast it is turning. Load and turning force (torque) help put other readings in context.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.