P0299 code: Turbocharger/Supercharger Underboost Condition
P0299 means turbocharger/Supercharger Underboost Condition. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0299 means
A turbocharged (or supercharged) engine's computer commands a target boost pressure and watches the boost sensor to confirm it arrives. P0299 sets when measured boost stays meaningfully below that target — the engine is asking for boost and not getting it. The most common real-world cause is a leak in the pressurized plumbing between the turbo and engine: a split intercooler hose, a loose clamp, a cracked charge pipe, or a leaking intercooler, all of which let boost escape before the engine sees it. Other causes include a wastegate stuck open (bleeding off boost it should be holding), a sticking variable-geometry (VGT) actuator or carboned-up vanes on diesels, a restricted air intake or clogged filter, a faulty boost-control solenoid, an exhaust restriction, or a genuinely worn turbo with damaged bearings or blades. Most vehicles respond with limp mode — power is limited to protect the engine — so the car feels dramatically slower even though it usually remains drivable. Because causes range from a loose clamp to a failed turbocharger, a boost-leak test is the smart first diagnostic step before any expensive parts are discussed.
P0299 symptoms
- Noticeable loss of power, especially under acceleration or uphill
- Reduced-power (limp) mode that may reset after a key cycle
- Hissing or whooshing sound under boost (a leak talking)
- Slower, lazier throttle response
- Worse fuel economy
- Whining or grinding turbo noises if the turbo itself is failing
What it costs to fix P0299
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0299 for my vehicle →How to fix P0299
Moderate — doable at home with common tools and patience
- Log boost against target and sanity-check the sensor
First confirm the boost sensor matches barometric pressure at key-on, engine off. Then log desired and actual boost through a safe acceleration in one gear with a helper watching. Boost short at every speed suggests a leak or a gate stuck open; slow spool-up on a diesel leans toward sticking variable vanes or a restriction.
- Pressure-test the charge piping and intercooler
Check the air filter and inlet hose first, then cap the intake ahead of the turbo and pressurize the charge system with a boost-leak tester, no higher than normal boost. Listen, and spray soapy water on couplers, clamps, the intercooler core and end tanks, and the throttle body seal. A little air passing open valves is normal; hissing at a joint is not.
- Check wastegate and VGT actuator travel
A wastegate held open by a seized pivot, a worn rattling bushing, or a weak actuator dumps boost before the engine sees it. On diesels, carbon-fouled variable-geometry vanes and sticky actuators are common. Command the actuator through its range with a scan tool where possible, and confirm the control hoses and solenoid are intact.
- Rule out an exhaust restriction
The turbine needs free exhaust flow to spin up. On diesels, check DPF soot load and differential pressure in live data; a heavily loaded filter cuts boost. On gasoline engines, a collapsed or clogged converter does the same, often with sluggish power and extra heat under the car. A back-pressure test confirms it.
- Inspect the turbo itself only after the rest checks out
With the engine off and cool, remove the inlet duct and look at the compressor wheel: chipped or bent blades, rub marks on the housing, or shaft play that lets the wheel touch the housing mean the turbo is worn. Heavy oil in the charge pipes and blue smoke support that. Find the cause, such as an oil feed problem, before fitting a new turbo.
DIY or shop? A home mechanic can cover a lot of P0299 — air filter, clamps and hoses, a boost-leak test, and a look at the compressor wheel — and leaks found that way are usually simple fixes. Actuator calibration, VGT cleaning, DPF diagnosis, and turbo replacement are where most people need a shop: they take bidirectional software, turbo removal, and care with the oil feed and drain lines. If you hear grinding from the turbo or see blue smoke, park it rather than finishing the turbo off.
Tools for the DIY steps: Scan tool with boost and actuator data · Boost-leak tester · Spray bottle with soapy water · Nut driver or hose clamp driver · Flashlight
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0299.
Start a case with P0299 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0299?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0299: common questions
What does P0299 mean and why is my car so slow?
The computer commanded boost and measured less than it asked for, so it set P0299 and, on most vehicles, limited power to protect the engine — that limp mode is why the car suddenly feels gutless. The boost itself is usually escaping through a leak or being lost to a control or turbo fault.
What's the most common cause of P0299?
A boost leak — a split intercooler hose, loose clamp, or cracked charge pipe letting pressurized air escape before it reaches the engine. That's why a boost-leak pressure test is the standard first step. Wastegate and VGT actuator faults are next in line, with an actual worn-out turbo further down the list than most people fear.
Does P0299 mean I need a new turbo?
Not usually. Plenty of P0299s are fixed with a hose, a clamp, an actuator, or a cleaning of stuck VGT vanes on diesels. The turbo itself is the last suspect, condemned only after the plumbing pressure-tests tight and the controls check out — so be wary of any diagnosis that jumps straight to turbo replacement.
How much does P0299 cost to fix?
The spread is unusually wide, which is why we don't pretend there's one number: a clamp or hose is a cheap fix, an actuator or boost solenoid is moderate, and a replacement turbocharger is a major repair. Paying for a proper boost-leak test first is the best money you can spend on this code.
Is it safe to keep driving in limp mode with P0299?
Redline can't make that call from the code alone. Limp mode cuts power to protect the engine, which also makes merging and passing hazardous, so get P0299 diagnosed promptly. Grinding noises, heavy smoke, or oil consumption point at turbo hardware failure — stop driving and have it towed.
Symptoms that trigger P0299
Drivers who get this code often notice one of these. Each has its own causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0299 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0299 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.