P0299: Turbocharger/Supercharger "A" Underboost Condition
P0299 means Turbocharger/Supercharger "A" Underboost Condition. Boost pressure from the turbocharger or supercharger is lower than the engine computer commanded.
On diesels, underboost is commonly caused by sticking variable-geometry vanes from soot. On petrol turbos, check hoses and the intercooler first.
Can I keep driving? Drivable with care. Diagnose soon: performance, economy or other components can be affected.
Common symptoms
- Check engine light on
- Noticeable loss of power
- Whistling or hissing under load
- Limp mode
- Black smoke on diesel engines
Possible causes
- Boost leak: split intercooler hose, loose clamp, cracked intercooler
- Wastegate stuck open or actuator fault
- Sticking variable-geometry turbo vanes (common on diesels)
- Worn turbocharger
- Restricted air filter or exhaust (for example a blocked diesel particulate filter)
- Faulty boost pressure sensor
How to diagnose P0299
- Inspect intercooler hoses and clamps for oil residue and splits.
- Pressure-test the intake (boost leak test).
- Compare desired and actual boost on a scan tool under load.
- Check wastegate or VGT actuator operation.
- Check turbo shaft play and for oil in the intake.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Symptoms linked to P0299
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.