P0299: Turbocharger/Supercharger A Underboost Condition
What to do
The car will drive but feel flat, often with a limp mode under load. Before accepting a turbocharger replacement, ask whether a boost leak test was performed and whether the wastegate and vane mechanism were checked for free movement — a split hose and a failed turbo produce the same code and differ enormously in cost.
What this code means
Boost pressure has fallen short of what the module commanded. This is among the most common forced-induction codes in service, and notably it is far more often a leak than a failed turbocharger. The charge system is a long path of pipes, clamps, an intercooler and a set of couplers, all of it under pressure and heat-cycled thousands of times — a split boost hose or a clamp that has relaxed will produce this code with a perfectly healthy turbo fitted.
On variable-geometry diesels, the second big cause is soot: vanes that have seized in a partly open position cannot generate the commanded boost. That is a genuine turbocharger fault, but it is sometimes recoverable by cleaning rather than replacement, which is worth establishing before a large quote is accepted.
Likely causes
Start here
- Boost leak in charge pipework · moderate
- Seized variable geometry turbocharger vanes · specialist
- Faulty wastegate actuator · moderate
- Failed boost control solenoid · moderate
- Disconnected wastegate vacuum hose · easy
Less common
- Restricted air filter · easy
- Blocked or failing intercooler · moderate
- Worn turbocharger · specialist
- Exhaust restriction from failed catalytic converter · moderate
- Faulty boost pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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