P0299 fault code: what it means

P0299: Turbo is not making the boost the engine computer asks for (underboost). Car feels flat and may go into limp mode.

Engine and gearbox (powertrain) · Costly if missed

Usual causes, most likely first

boost leak from intercooler hoses or clamps
wastegate or variable vanes sticking
vacuum hose or boost control solenoid fault
worn turbocharger

P0299 by make

Audi

Turbo not making the boost asked for. On TSI/TFSI the diverter valve and wastegate are the usual suspects; on TDI a boost leak or sticking turbo vanes.

Usual causes: torn diverter valve diaphragm (petrol TSI/TFSI); boost leak: split intercooler hose or cracked charge pipe (most likely on TDI); lazy or blocked boost control valve (N75); sticking wastegate (petrol) or VNT vanes (TDI)

BMW

Turbo underboost: boost lower than asked. On BMW petrol turbos (N54 / N55 / N20) and diesels, a boost leak or wastegate is usual.

Usual causes: boost leak (split charge pipe or intercooler hose); worn wastegate (N54 rattle) or wastegate actuator; vacuum line or solenoid fault; turbo wear

Ford

Turbo underboost: boost stayed below target. Common on Ranger/Everest diesels and on EcoBoost petrols; usually limp mode or flat power.

Usual causes: split intercooler hose or loose boost pipe; sticking turbo vanes or faulty electronic turbo actuator (diesel); worn or rattling wastegate / failed vacuum check valve (EcoBoost); worn turbo

GWM

Turbo underboost.

Usual causes: split intercooler/boost hose or loose clamp; sticking VGT vanes or actuator; boost control solenoid or vacuum hose

Haval

Turbo underboost on the 1.5T/2.0T petrol.

Usual causes: sticking or faulty electronic wastegate actuator; boost hose or intercooler leak; diverter (bypass) valve leaking

Holden

Turbo underboost: boost stayed below target. On Captiva diesels a split turbo-to-intake trunking is a known cause, with hissing and black smoke.

Usual causes: split turbo-to-intake trunking or intercooler hose; worn or leaking turbo; turbo vane or actuator fault

Honda

Turbo underboost on the Honda 1.5 turbo (L15B): boost is lower than the ECU expects. The electronic wastegate linkage is a known weak point.

Usual causes: boost leak at intercooler or intake hoses; worn electronic wastegate actuator or linkage; turbocharger fault

Hyundai

Turbo underboost: not making the boost asked for. Very common on 1.6 T-GDI Tucson/Kona and 2.0 T-GDI.

Usual causes: boost leak (split intercooler hose or leaking intercooler); wastegate actuator rod stuck or actuator failed; faulty boost control (vacuum) solenoid; turbo oil feed leak or worn turbo bearings (2.0 T-GDI)

Isuzu

Turbo underboost. On D-Max/MU-X often sooted VGT vanes, a boost leak or the VGT actuator.

Usual causes: split intercooler/boost hose or loose clamp; sticking VGT vanes (soot); VGT actuator or solenoid; blocked air filter

Jeep

Turbo underboost on CRD diesels.

Usual causes: split boost or intercooler hose; sticking turbo vanes/actuator; boost control solenoid or vacuum leak

Land Rover

Turbo underboost: boost pressure stays below target. Common on Land Rover diesels when charge air leaks or the turbo cannot build pressure.

Usual causes: split turbo-to-intercooler hose; cracked inlet manifold or intercooler; turbo actuator or vane fault; worn turbo

LDV

Turbo underboost.

Usual causes: split intercooler/boost hose or loose clamp; sticking VGT vanes or actuator; boost control solenoid or vacuum hose

Mazda

SkyActiv-D: small turbo underboost. Boost below target; split hoses and vacuum lines first, then the turbo.

Usual causes: boost leak / split intake hose; vacuum or pressure pipe to the regulating or bypass valve; exhaust leak before the turbo; regulating/bypass solenoid valve or turbo fault

Mercedes-Benz

Turbo underboost (low boost). On Mercedes diesels usually a boost leak or a sticking turbo actuator.

Usual causes: charge air hose or intercooler leak; sticking turbo vanes/actuator; blocked DPF or exhaust restriction; faulty boost pressure sensor

MG

Turbo underboost on MG HS/ZS turbo petrols.

Usual causes: sticking or faulty wastegate actuator; boost hose or intercooler leak; diverter valve leaking

Mini

Turbo underboost (Cooper S / JCW / diesel). Usually a boost leak or wastegate fault before the turbo itself.

Usual causes: boost leak (charge pipe, intercooler hose); wastegate or its actuator/solenoid; diverter (blow-off) valve leaking; turbo wear

Mitsubishi

Turbo underboost: boost below target. Common on Triton/Pajero Sport with VGT sticking or boost leaks.

Usual causes: boost leak (split intercooler hose or loose clamp); VGT vanes or actuator sticking; faulty boost control solenoid or vacuum leak; worn turbo

Skoda

Turbo not making the boost asked for. On TSI/TFSI the diverter valve and wastegate are the usual suspects; on TDI a boost leak or sticking turbo vanes.

Subaru

Turbo underboost: boost stayed below target (Subaru turbo models).

Usual causes: boost leak (split intercooler hose or coupler); wastegate stuck open; faulty boost control solenoid; worn turbo

Volkswagen

Turbo not making the boost asked for. On TSI/TFSI the diverter valve and wastegate are the usual suspects; on TDI a boost leak or sticking turbo vanes.

Volvo

Turbo underboost: boost stays below target. On Volvo D5 diesels usually a boost leak or turbo actuator problem; power drops into limp mode.

Usual causes: split boost hose or cracked intercooler; faulty electronic turbo actuator; sticking turbo vanes; worn turbo

What the repair usually costs

CVT valve body replacement (remanufactured, in car)NZ$1,280–NZ$2,420 · A$1,200–A$2,400
Automatic transmission rebuild, 6-speed and up (sent to specialist)NZ$7,190–NZ$13,080 · A$6,190–A$11,830
DSG / dual-clutch mechatronic unit replacement (new or reman)NZ$4,300–NZ$7,160 · A$3,750–A$6,390
DSG mechatronic repair / rebuild (unit sent to specialist)NZ$2,070–NZ$4,800 · A$1,890–A$4,250

Not sure what P0299 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.