P0299
Turbocharger/Supercharger A Underboost Condition
Published · Reviewed and updated
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.
A diagnostic starting point: Split, loose or swollen charge-air hose or intercooler leak. Start by asking: Does saved data show actual boost below request under valid test conditions? Illustrative parts budgets span $20–$3500 USD, with diagnosis, labor and taxes extra.
Quick answers about P0299
- What does P0299 mean?
- 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.
- What should I check first for P0299?
- One starting point is 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. The code alone does not identify a failed part; follow the procedure for your vehicle.
- Can I drive with P0299?
- 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.
- How much does it cost to fix P0299?
- Illustrative parts budgets in this guide span $20–$3500 USD. Diagnosis, labor and taxes are extra. 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.
- How do I diagnose P0299?
- Start with: 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.
Watch the P0299 videos
Full walkthrough — 9:29. Watch on YouTube
What P0299 actually means
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.
Symptoms
- Weak acceleration or reduced-power modeThe computer may limit fuel and torque when measured airflow or boost cannot meet the request.
- Whooshing, hissing or a new whistle under loadA split charge hose or loose connection may leak only after pressure rises.
- Black smoke on a diesel or abnormal exhaust smokeToo little air for commanded fuel can create soot; blue smoke or oil consumption needs urgent turbo inspection.
- Intermittent warning light during hills or hard accelerationThe monitor often runs only when load and requested boost are high enough.
- Sometimes normal light-throttle drivingA substantial leak or weak actuator can remain hidden while the engine operates near atmospheric pressure.
Possible causes and what to check
This is a practical diagnostic order, not measured failure rates. Follow the tests and priorities specified for your vehicle; a code alone does not identify a failed part.
The deciding graph: requested boost versus actual pressure
Illustrative graph, not a recording from your vehicle or a universal service limit. Confirm the test conditions, units and acceptance criteria in the applicable service procedure.
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.
How to diagnose it, in order
-
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.Yes → go to step 2No → Check intermittent data, enabling conditions and related codes
-
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.Yes → go to step 3No → Repair the restriction, collapsed hose or charge-air leak
-
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.Yes → go to step 4No → Repair the vacuum, solenoid, actuator, linkage or control circuit
-
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.Yes → go to step 5No → Repair the pressure-sensor circuit or replace the proven biased sensor
-
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.Yes → Check application-specific software and airflow modelingNo → Repair the proven restriction, engine fault or turbocharger damage
Measure the pressure gap, contain the air, prove the control system and verify the sensors before blaming the turbocharger.
What you need to do this yourself
- A scan tool that reads live data — Choose vehicle-compatible access to the live data, freeze frame and monitor results required by the diagnostic procedure. Some checks also need bidirectional control.
- Digital multimeter — Use the specified meter and test method for electrical checks. Follow circuit diagrams and avoid applying an unsuitable test load to a computer driver.
- Vehicle-specific service information — Confirm the procedure, safety precautions, tools and acceptance limits for the exact year, model and engine.
Some links may be affiliate links. They cost you nothing extra and do not change which tools are recommended — the diagnostic order on this site is the same either way.
Illustrative repair budgets
These are rough US planning examples, not quotes or measured repair averages. Parts and labor are separate; diagnosis, taxes, difficult access and additional repairs can increase the total.
| Repair | Parts (USD) | Labor time |
|---|---|---|
| Charge hose, clamp or accessible boost-leak repair A pressure leak is often far less expensive than the turbocharger it makes look weak. |
$20–$350 | 1.0 h |
| Boost-control hose, solenoid or actuator Some actuators are serviced separately; others are calibrated with the turbo assembly. |
$30–$700 | 1.5 h |
| MAP, boost or charge-pressure sensor Replacement belongs after pressure plausibility and circuit checks. |
$30–$250 | 0.7 h |
| Intake or exhaust restriction repair The range spans an air filter or collapsed inlet to an emissions-filter repair. |
$25–$1800 | 3.0 h |
| Turbocharger assembly Confirm the failure and its oil, air or exhaust cause so the replacement is not damaged again. |
$500–$3500 | 7.0 h |
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.
P0299 video summary · 1:10
A brief introduction to the code and a diagnostic starting point. Use the full guide and vehicle-specific service information for the complete procedure.
Written diagnostic walkthrough
Current written guidance organized by topic. This text may include corrections made after a video was published and is not a verbatim transcript of the archived video.
Meaning and driving guidance
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.
How it is measured
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.
Symptoms
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.
Possible causes
Here is a practical order for checking the possible causes. These are diagnostic priorities, not measured failure rates.
Check 1: 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.
Check 2: Wastegate, bypass, vane actuator or control-solenoid fault. Lost vacuum, a damaged hose, binding linkage or an electronic actuator fault can bleed boost away.
Check 3: Restricted air filter, turbo inlet or exhaust flow. A collapsed inlet hose, blocked filter, loaded particulate filter or exhaust restriction limits energy and airflow.
Check 4: 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.
Check 5: Worn, damaged or sticking turbocharger assembly. Impeller damage, excessive shaft play, a seized mechanism or lubrication trouble belongs after external checks.
Check 6: Engine breathing, EGR, PCV or calibration issue. Airflow-model errors and application-specific software can fail the same requested-versus-actual comparison.
Use the test results to choose the repair. A position in this list does not prove that a part has failed.
Illustrative diagnostic pattern
This illustrative graph explains a diagnostic pattern. Use the vehicle-specific procedure to interpret it.
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.
Diagnostic steps
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.
Illustrative repair budgets
These are illustrative US parts budgets with labor shown separately. Diagnosis, taxes, access and additional repairs can change the total.
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.
Sources and application limits
This legacy guide has not yet had a page-specific source list added. Check the factory service information for your exact year, make, model and engine before acting on a test or specification.