Engine
How does a turbocharger work and what does P0299 mean?
A turbocharger uses the exhaust gases to compress the intake air so the engine makes more power. If the pressure the control unit measures is lower than it asks for, it stores P0299 (underboost) and usually limits power; if it is higher, P0234. Often the cause is not the turbo itself but a split hose or the boost control.
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How is boost controlled?
With a wastegate or, on many diesels, with variable geometry vanes that change how the gases hit the turbine. An electric or vacuum actuator moves them as the control unit asks.
What causes underboost?
Leaks in the hoses or the intercooler, variable geometry stuck with soot, a failed actuator or its sensor, a badly clogged particulate filter or, in the end, wear of the turbo itself.
A worn turbo usually gives other clues: whistling, blue smoke from oil or oil consumption.
How do you look after a turbo?
Change the oil on time and to the manufacturer's specification, let the engine warm up before working it hard and, after very demanding use, let it idle a few seconds before switching off if the manual recommends it.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0299Turbocharger/supercharger A: underboost
- P0234Turbocharger/supercharger A: overboost
- P0033Turbocharger/supercharger bypass valve A, control circuit: malfunction
- P0045Turbocharger/supercharger boost control A, circuit open
- P2563Turbocharger boost control position sensor A, circuit: range/performance
Related symptoms
- Car loses power: what limp mode is
- Blue smoke from the exhaust: the engine is burning oil
- Black smoke from the exhaust: causes and what to do
Learn more
See what your car is saying
With the ECO-LITE, your workshop can record remotely, if the car publishes them, the requested and actual boost during a road test.
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Frequently asked questions
Can I drive with P0299?
Gently and to the workshop, yes. If there is blue smoke, metallic noises or oil loss, stop.
Can a split hose cause P0299?
Yes, it is one of the most common causes.
What does P0234 mean?
That boost pressure is higher than the control unit expects; it is usually down to the boost control.