P0299 Code: Turbocharger/Supercharger A Underboost Condition
The turbo or supercharger isn't building the boost pressure the engine computer is asking for.
At a glance
Severity: Moderate
- Meaning
- Turbocharger/Supercharger A Underboost Condition
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $5–$4,500
- DIY difficulty
- Hard
On a boosted engine, the engine computer sets a target boost pressure for each driving condition and controls the wastegate or variable-vane turbo to reach it, while a boost pressure sensor reports what is actually happening in the intake. P0299 sets when actual boost stays below the target by a calibrated margin for long enough. Most of the time the turbo itself is fine: pressurized air is escaping through a split hose, loose clamp or cracked intercooler, or the wastegate or vane mechanism isn't responding. On diesels, a clogged particulate filter or sooted-up variable vanes are also common. Many vehicles cut power into a limp mode to protect the engine once the code sets.
Can I keep driving? You can usually drive gently to a shop, but expect limited power, so avoid highway merging, passing and towing. If you hear loud whining or grinding, see blue smoke or the oil light comes on, stop immediately to avoid wrecking the turbo or engine.
How to read P0299
- P Powertrain
- 0 Generic (SAE)
- 2 Fuel & air (injector circuit)
- 99 Specific fault
Symptoms
- Check engine light on
- Noticeable loss of power, often limp mode with capped boost
- Hissing, whooshing or whistling sound under acceleration
- Slow acceleration when merging or climbing hills
- Black smoke on diesels under load
- Worse fuel economy
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Boost leak: split or popped charge-air hose, loose clamp, cracked intercooler or charge pipe
- Wastegate or variable-vane (VGT) mechanism sticking, or a faulty control solenoid or vacuum line
- Faulty boost pressure or MAP sensor, or its wiring
- Exhaust restriction: clogged diesel particulate filter or catalytic converter
- Worn or damaged turbocharger (bearing wear, damaged compressor wheel)
- Restricted air intake, such as a clogged air filter or collapsed intake hose
- EGR valve stuck open on diesels
Diagnosis step by step
Compare desired and actual boost
With a scan tool that shows desired and actual boost, record a safe, legal acceleration in a middle gear. Boost that builds slowly and never reaches target points toward a leak or a lazy actuator; boost that suddenly drops off at higher rpm suggests a hose that balloons or pops under pressure.
Tools: OBD-II scanner
Inspect all charge-air plumbing
With the engine off and cool, check every hose, coupler and clamp between the turbo, intercooler and throttle body. Oily film on the outside of a joint, a coupler that has slid partly off or a crack at the intercooler end tanks are typical findings.
Tools: Flashlight, Screwdriver
Pressure-test the intake system
Seal the intake with a boost-leak tester or a smoke machine with a suitable adapter and apply modest pressure, around 15 to 20 psi and never more than the engine's rated boost. Listen and spray soapy water on joints to find escaping air.
Tools: Smoke machine
Check the wastegate or vane actuator
On vacuum-operated actuators, apply vacuum with a hand pump: the rod should move smoothly and hold vacuum. On electronic actuators, run the actuator test in the scan tool and watch for full, smooth travel. Sticking diesel vanes often respond to movement but hang up when hot.
Tools: Vacuum gauge, OBD-II scanner
Verify the boost pressure sensor
With the key on and the engine off, the boost sensor should read the same as barometric pressure, roughly 14.7 psi absolute at sea level. A sensor that reads noticeably off at rest can make the computer think the turbo is underperforming.
Tools: OBD-II scanner, Multimeter
Rule out exhaust restriction
On diesels, check the particulate filter differential pressure and soot load in live data; a clogged filter chokes the turbine. On gasoline engines, a collapsed or melted catalytic converter causes the same loss of drive.
Tools: OBD-II scanner
Inspect the turbocharger itself
With the engine off and cool, remove the intake pipe at the compressor inlet. The wheel should spin freely, a little side-to-side play is normal but the blades must not touch the housing, and there should be no chipped blades or pooled oil.
Tools: Flashlight, Gloves
Where the parts are
- 1MAF sensor
- 2Turbocharger
- 3Throttle body
- 4Intake manifold
- 5Fuel injector
- 6EGR valve
- 7Fuel pump
- 8Thermostat
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reseat or replace a charge-air hose clamp | Yes | $5–$60 |
| Replace split charge-air hose or coupler | Yes | $80–$400 |
| Replace boost control solenoid or wastegate actuator | No | $150–$800 |
| Replace intercooler | No | $400–$1,400 |
| Replace turbocharger | No | $1,500–$4,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Volkswagen
On VW TDI diesels, soot buildup in the variable-vane turbo is a well-known cause of underboost, especially on vehicles driven mostly at low speed. Before condemning the turbo, check that the vane actuator moves freely across its full range.
Chevrolet
On the 1.4-liter turbo four-cylinder used in the Cruze, Sonic and Trax, P0299 is frequently traced to leaking charge-air hoses or connections and to wastegate problems. Inspect the boost plumbing and the wastegate linkage before replacing the turbocharger.
Field data
| Chevrolet | 30 | ||
|---|---|---|---|
| Ford | 28 | Escape, Edge, F-150 SUPERCAB | |
| Honda | 9 | Accord, Cr-V, Civic Hybrid | |
| Ram | 6 | 1500, 2500, Promaster | |
| Volkswagen | 4 | Passat, Jetta, Jetta Sportwagen | |
| Dodge | 2 | Dart | |
| Hyundai | 2 | Santa Fe, Tucson |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
A lit check engine light fails OBD-II emissions testing in states that require it. On diesels, underboost can also cause heavy smoke, which may fail a visual or opacity check where one is performed.
Frequently asked questions
Does P0299 mean my turbo is dead?
Usually not. Boost leaks and wastegate or vane control problems are far more common than a failed turbocharger. A turbo that is truly worn out tends to show other signs too, such as loud whining, oil in the intake pipes or blue smoke.
Why does P0299 only show up at high altitude or in hot weather?
Thin or hot air makes the turbo work harder to reach the same boost target. A marginal system, such as a small leak or a weak actuator, may cope at sea level but fall short in the mountains or on a hot day.
Can I clear P0299 and keep driving?
Clearing it may restore full power until the fault is detected again, but the cause is still there. Driving with a boost leak or sticking wastegate for a long time can overwork the turbo and hurt fuel economy.
Can a clogged DPF cause P0299 on my diesel?
Yes. A plugged particulate filter creates high back pressure, so the exhaust can't spin the turbine properly and boost falls short. Check the soot load and differential pressure before replacing turbo parts.