# P0299: Turbocharger/Supercharger "A" Underboost Condition **Verdict:** Drive to a shop this week Air intake - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$4,000 - **Urgency:** This week - **Most likely:** Boost leak or wastegate problem - **DIY?:** Steps 1-2 ## Quick answer P0299 means the turbocharger or supercharger is not making as much boost as the engine computer asked for. The engine feels down on power and may go into limp mode. A leak in the boost pipes or a wastegate problem is the usual cause, and a failing turbo is less common. ## What does P0299 mean? A turbocharger uses exhaust flow to spin a compressor that packs extra air into the engine, and a supercharger does the same job driven by a belt. More air, matched with more fuel, means more power from a smaller engine. The engine computer sets a target boost pressure for current conditions and controls it with a wastegate, a bypass valve or, on many diesels, variable turbine vanes. A boost or manifold pressure sensor reports actual boost. P0299 sets when actual boost stays below the target by more than a calibrated amount for a set time, usually during acceleration when boost is requested. "A" refers to the first or only turbo or supercharger; twin-turbo engines may report the second unit separately. To protect the engine, many vehicles cut power or enter limp mode, which often lasts until the engine is switched off and restarted. ## What are the symptoms of P0299? - Check engine light on - Noticeable loss of power, especially when accelerating - Limp mode or reduced-power warning - Hissing or whooshing sound when accelerating - Whining, grinding or smoke from the turbo if it is failing ## What causes P0299? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Boost leak from a cracked hose, loose clamp or leaking intercooler** (most common). Pressurized air escapes through a split coupler, loose clamp or cracked intercooler before reaching the engine, so the turbo cannot hold target boost. Rubber and plastic charge pipes harden with heat and age, and couplers can blow off under load. Listen for a hiss or whoosh under acceleration and look for oily residue around pipe joints and the intercooler. 2. **Wastegate stuck open or a bad wastegate actuator** (common). The wastegate is a flap that lets exhaust bypass the turbine to limit boost. If it sticks open from carbon or rust, or its vacuum or electronic actuator fails, exhaust skips the turbo and boost stays low. On diesels with variable-vane turbos, soot-stuck vanes cause the same problem. A shop checks that the gate or vanes move fully when commanded. 3. **Faulty boost control solenoid or vacuum line** (common). On many engines a solenoid valve meters vacuum or boost pressure to the wastegate actuator, following commands from the engine computer. A split or disconnected vacuum line, a weak vacuum pump on diesels, or a solenoid stuck in one position keeps the wastegate from closing. Cracked lines are common on older engines, where rubber hoses harden from years of heat. 4. **Leaking diverter or blow-off valve** (less common). A diverter or blow-off valve vents boost when the throttle closes so the compressor is not stressed. If its rubber diaphragm tears or the valve sticks open, boost leaks back into the intake during acceleration. This is a well-known failure on some Volkswagen and Audi gasoline turbo engines, and revised replacement valves exist for several of them. 5. **Worn or damaged turbocharger** (less common). Turbos spin at very high speed on a thin film of oil, so oil starvation, sludge or a foreign object can wear the bearings or chip the blades. Signs include whining or siren noises, blue or gray smoke, oil pooling in the intake pipes and shaft play felt by hand. High-mileage engines with stretched oil changes are most at risk. 6. **Restricted air filter or exhaust** (rare). A badly clogged air filter, a crushed intake duct, a plugged catalytic converter or, on diesels, a soot-loaded particulate filter can restrict flow enough that the turbo cannot reach target boost. Restriction problems often bring other codes or warnings with them. Check the air filter first, since it is cheap and quick, before testing exhaust back pressure. ## How do you diagnose P0299? 1. Inspect boost hoses, clamps and the intercooler for cracks, loose clamps and oil residue. 2. Compare desired and actual boost pressure on a scan tool during a safe road test. 3. Have a shop pressure-test the intake (boost leak test) to find leaks. 4. Check wastegate movement and test the boost control solenoid and vacuum lines. 5. Remove the intake pipe and check the turbo shaft for play and damaged blades. ## How do you fix P0299, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace a boost hose, clamp or coupler | $100-$400 | Most common and least expensive repair. | | Replace boost control solenoid or diverter valve | $150-$500 | Restores control of the wastegate or stops a valve leak. | | Replace wastegate actuator | $250-$900 | Some electronic actuators are only sold with the turbo. | | Replace the turbocharger | $1,500-$4,000 | Only after leaks and controls are ruled out. | ## Is it safe to drive with P0299? > **Drive to a shop this week.** You can usually drive it gently, but limited power makes merging and passing risky. Stop driving if you see heavy smoke or hear grinding from the turbo, because debris can damage the engine. ## Will P0299 fail an emissions test? An OBD-based emissions test fails a car showing P0299 with the check engine light on. On a diesel, low boost can also raise smoke, which matters in places that still run opacity tests. After the repair, drive until the readiness monitors complete; some diesels may also need to finish a particulate filter regeneration before every monitor reports ready. ## After the repair: clearing P0299 Clear the code and road-test with a scan tool, comparing desired and actual boost during a firm, safe acceleration. Actual boost should rise to meet the target quickly and hold it without overshooting. If limp mode does not return and the code stays away through a week of normal driving, including highway merges and hills, the leak or control fault is fixed. ## How to prevent P0299 - Change engine oil on schedule with the specified grade; turbo bearings depend on clean oil. - After towing or hard highway runs, let the engine idle briefly before shutting it off. - Replace the air filter on time and keep the intake sealed so dirt never reaches the compressor. - Check intercooler hoses and clamps at oil changes for oil residue, cracks or looseness. - On diesels, mix in regular highway driving to limit soot that sticks turbo vanes. ## Codes often seen with P0299 - [P0101](/codes/p0101): Mass or Volume Air Flow "A" Circuit Range/Performance - [P0171](/codes/p0171): System Too Lean (Bank 1) - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) ## Frequently asked questions ### Does P0299 mean my turbo is bad? Not usually; a boost leak or wastegate problem is more common, and the turbo itself is often fine. Replacing a healthy turbo will not fix a split coupler or stuck solenoid. A boost leak test and control checks should always come before turbo replacement, and real turbo failure usually brings noise, smoke or shaft play. ### Can I drive with P0299? Yes, gently, for short trips. The car will lack power and may go into limp mode, which makes merging and passing risky. Get it checked soon, and stop driving if you hear new grinding or whining from the turbo or see heavy smoke, because turbo debris can damage the engine. ### What does underboost mean? Underboost means the turbo or supercharger is making less pressure than the engine computer commanded. Less boost means less air in the cylinders, so the engine makes less power. The computer compares desired and actual boost, and when the gap stays too large for too long it sets P0299 and often limits power. ### How much does it cost to fix P0299? Most P0299 repairs cost $100 to $500, because boost leaks, clamps, solenoids and diverter valves are the usual causes. A wastegate actuator runs $250 to $900. Replacing the turbocharger costs $1,500 to $4,000 and should only happen after a boost leak test and control checks rule out the cheaper causes. ### How do I find a boost leak? The reliable way is a boost leak test, where a shop seals the intake and pressurizes it with shop air or smoke. Leaks then hiss or show smoke at the bad joint. At home you can check clamps, look for oily residue and listen for hissing under load, but small leaks are easy to miss. ### Can a clogged air filter cause P0299? It can, though it is not the usual cause. A badly clogged filter starves the turbo of air, so it struggles to reach target boost, especially under hard acceleration or at high altitude. A filter costs little and takes minutes to check, so look at it before booking a boost leak test. ### Why does P0299 come and go? Intermittent P0299 usually means a leak or control part that fails only under certain conditions. A coupler may only blow open under high boost, a wastegate may stick only when hot, or a diaphragm may leak only at higher pressure. Note when it happens, such as hot weather or towing, and tell the shop. ### Is P0299 common on diesels? Yes, P0299 is a familiar code on turbo diesels. Besides boost leaks, diesel turbos with variable vanes can stick when soot builds up, often on trucks used mainly for short trips. A loaded particulate filter or an EGR fault can also affect boost, so diesel diagnosis usually checks those systems as well. ### Will P0299 pass inspection? No, an active P0299 with the check engine light on will fail an OBD-based emissions test. On a diesel, low boost can also raise smoke. Repair the leak or control fault, clear the code, and drive normally until a scan tool shows the readiness monitors complete before you return for the retest. ### Can I fix P0299 myself? Sometimes, if the cause is a loose clamp, cracked coupler or split vacuum line you can see and reach. Those parts are inexpensive and need only basic hand tools. Testing a boost control solenoid, adjusting a wastegate or replacing a turbocharger takes a scan tool and experience, so leave those jobs to a shop. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other air intake codes - [P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High](https://diagxcar.com/codes/p0108) - [P0112 Intake Air Temperature Sensor 1 Circuit Low (Bank 1)](https://diagxcar.com/codes/p0112) - [P0113 Intake Air Temperature Sensor 1 Circuit High (Bank 1)](https://diagxcar.com/codes/p0113) - [P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0121) - [P0122 Throttle/Pedal Position Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0122) - [P0123 Throttle/Pedal Position Sensor/Switch "A" Circuit High](https://diagxcar.com/codes/p0123) - [P0201 Injector Circuit/Open - Cylinder 1](https://diagxcar.com/codes/p0201) - [P0217 Engine Coolant Over Temperature Condition](https://diagxcar.com/codes/p0217) - [P0230 Fuel Pump Primary Circuit](https://diagxcar.com/codes/p0230) - [P0261 Cylinder 1 Injector "A" Circuit Low](https://diagxcar.com/codes/p0261) ## Symptoms - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) - [Why is blue smoke coming from my exhaust?](https://diagxcar.com/symptoms/blue-smoke-from-exhaust) - [Why is black smoke coming from my exhaust?](https://diagxcar.com/symptoms/black-smoke-from-exhaust) - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) - [Why does my car whine when I accelerate?](https://diagxcar.com/symptoms/whining-noise-when-accelerating) --- Source page: https://diagxcar.com/codes/p0299 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.