P0299

00:00What this code means

Code P0299. Turbocharger/Supercharger A Underboost Condition.

In plain English: the engine computer commanded more boost than the intake-pressure sensors reported; P0299 measures a boost shortfall and does not automatically mean the turbocharger failed.

A gentle short trip may be possible if the engine runs smoothly with no smoke, oil warning or abnormal turbo noise. Stop and arrange a tow for heavy smoke, scraping or siren-like noise, rapidly falling oil level, severe power loss or uncontrolled engine speed. Avoid hard acceleration until the cause is known.

00:40How the test actually works

Here's what your engine computer is actually measuring.

Exhaust energy or mechanical drive spins a compressor that pushes more air through the charge-air path and into the engine. The computer commands a boost target, controls a wastegate, bypass or variable vanes, and watches manifold or charge-pressure sensors. Under load, actual pressure should rise close to the requested value. When actual boost stays too far below the target for the calibrated time, the computer stores P0299.

P0299 sets when the difference between requested and measured boost exceeds the vehicle's allowed error under enabling load, speed and temperature conditions. Manufacturer examples use different pressure gaps and timers, so a universal boost number is not a valid pass-fail specification. The code proves an underboost result, not whether air escaped, the control system failed, a sensor lied or the compressor could not produce pressure.

So the code is not a part failure report. It's a performance measurement that came back under spec.

01:47Symptoms

What you'll usually notice, beyond the light itself.

Weak acceleration or reduced-power mode. The computer may limit fuel and torque when measured airflow or boost cannot meet the request.

Whooshing, hissing or a new whistle under load. A split charge hose or loose connection may leak only after pressure rises.

Black smoke on a diesel or abnormal exhaust smoke. Too little air for commanded fuel can create soot; blue smoke or oil consumption needs urgent turbo inspection.

Intermittent warning light during hills or hard acceleration. The monitor often runs only when load and requested boost are high enough.

Sometimes normal light-throttle driving. A substantial leak or weak actuator can remain hidden while the engine operates near atmospheric pressure.

02:40Most likely causes, ranked

Now the part you came for: what actually causes this, ranked by how often it turns out to be the culprit.

30 percent of the time, it's this: Split, loose or swollen charge-air hose or intercooler leak. Pressurized air can escape between the compressor and intake even when the hose looks normal at idle.

22 percent of the time, it's this: Wastegate, bypass, vane actuator or control-solenoid fault. Lost vacuum, a damaged hose, binding linkage or an electronic actuator fault can bleed boost away.

13 percent of the time, it's this: Restricted air filter, turbo inlet or exhaust flow. A collapsed inlet hose, blocked filter, loaded particulate filter or exhaust restriction limits energy and airflow.

12 percent of the time, it's this: Biased boost, MAP or charge-pressure sensor and circuit. A pressure reading that is plausible but wrong can report underboost even when the air path is intact.

13 percent of the time, it's this: Worn, damaged or sticking turbocharger assembly. Impeller damage, excessive shaft play, a seized mechanism or lubrication trouble belongs after external checks.

10 percent of the time, it's this: Engine breathing, EGR, PCV or calibration issue. Airflow-model errors and application-specific software can fail the same requested-versus-actual comparison.

Notice that the most expensive repair is not the most likely one. That matters, because the cheap checks come first.

04:19The measurement that decides it

This is the single measurement that tells you whether you need the expensive part or the cheap one.

This is an illustrative graph, not a universal specification. Save the freeze frame, then graph requested boost and actual manifold or charge pressure during the manufacturer's controlled road or dynamometer test. Use absolute or gauge pressure consistently.

The known-good actual trace follows the request closely as load rises, with only a small calibrated lag. That shows the complete air path and control system can meet this command at this moment.

The underboost trace rises but remains well below the request. That confirms the symptom, but the graph alone cannot separate a leaking hose, open wastegate, restricted inlet, biased sensor or weak turbocharger.

First verify that key-on engine-off pressure agrees with local barometric pressure. Then pressure- or smoke-test within the manufacturer's limit while watching actuator command and position; those results decide which branch failed.

05:24Diagnostic order

So here is the order to actually test this, cheapest and most likely first.

Step 1. Does saved data show actual boost below request under valid test conditions? Save every code and freeze frame before clearing anything. Reproduce the fault only with the specified load test and compare pressure units correctly; a no-load throttle snap may never request useful boost.

Step 2. Do the filter, inlet, charge pipes and intercooler pass inspection and leak testing? Inspect both sides of every hose, clamp and quick connector, including oil-marked or abraded areas. Pressure- or smoke-test only at the manufacturer's safe limit because an excessive test can damage the system.

Step 3. Do vacuum supply, solenoid command and wastegate or vane movement meet specification? Test the control design actually fitted. Compare commanded and actual actuator position, check vacuum retention where used, and confirm the linkage moves through its specified range without binding.

Step 4. Are boost and barometric pressure sensors accurate and electrically stable? With key on and engine off, related pressure sensors should agree within the vehicle specification and local conditions. Verify supply, ground and signal, then compare with a trusted mechanical pressure measurement if required.

Step 5. Do exhaust flow, engine breathing and the turbocharger pass mechanical tests? Follow factory checks for exhaust restriction, EGR and PCV behavior, impeller condition, shaft play, oil supply and variable-vane movement. Do not run the engine with intake plumbing removed unless the procedure explicitly permits it.

Measure the pressure gap, contain the air, prove the control system and verify the sensors before blaming the turbocharger.

07:24Repair costs

What this costs to put right, in US dollars, parts and labor.

Charge hose, clamp or accessible boost-leak repair: 20 to 350 dollars in parts, plus about 1.0 hours of labor. A pressure leak is often far less expensive than the turbocharger it makes look weak.

Boost-control hose, solenoid or actuator: 30 to 700 dollars in parts, plus about 1.5 hours of labor. Some actuators are serviced separately; others are calibrated with the turbo assembly.

MAP, boost or charge-pressure sensor: 30 to 250 dollars in parts, plus about 0.7 hours of labor. Replacement belongs after pressure plausibility and circuit checks.

Intake or exhaust restriction repair: 25 to 1800 dollars in parts, plus about 3.0 hours of labor. The range spans an air filter or collapsed inlet to an emissions-filter repair.

Turbocharger assembly: 500 to 3500 dollars in parts, plus about 7.0 hours of labor. Confirm the failure and its oil, air or exhaust cause so the replacement is not damaged again.

P0299 can be a loose clamp or a major turbo repair. A controlled boost graph followed by leak, actuator and sensor tests keeps that price range from becoming a guess.

08:52Recap and related codes

Quick recap. P0299 means actual boost stayed below the computer's request; it does not automatically mean the turbocharger failed. Save the load conditions, compare requested and actual pressure, test the complete air path, prove wastegate or vane control, verify sensor accuracy, then inspect restrictions and the turbocharger last.

If your scan tool showed a related code alongside this one, check those too: P0234, P0236, P2263, P00AF.

Codes are on screen and linked below.