OBD-II · Engine and powertrain (P)
P0299
Turbocharger underboost condition
What it means
Boost pressure is lower than the engine computer's target.
Symptoms
- loss of power, often limp mode
- whistling or hissing under acceleration (boost leak)
- black smoke
- engine warning light
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | split boost hose or loose intercooler clamp (look for oily hoses) |
| 02 | sticking variable turbine vanes or actuator fault |
| 03 | boost control solenoid fault or vacuum supply problem |
| 04 | blocked air filter or intake |
| 05 | restricted exhaust or blocked DPF |
| 06 | worn turbo (shaft play, oil leaks) |
| 07 | EGR stuck open |
What to check, step by step
- 01Inspect all boost hoses, intercooler and clamps; oil-soaked or split hoses are the usual culprit.
- 02Smoke- or pressure-test the intake/boost system.
- 03Compare requested and actual boost in live data and check the actuator movement.
- 04Check vacuum supply and the boost control solenoid on vacuum-operated turbos.
- 05Check DPF load and exhaust back pressure.
- 06Check turbo shaft play and for oil in the intake.