Turbo/Supercharger Underboost
The P0299 code indicates that the engine's turbocharger or supercharger is not producing the expected amount of boost pressure. The Powertrain Control Module (PCM) sets this code when the actual boost pressure falls below the commanded target pressure for a specified amount of time.
This code should be addressed promptly as driving with an underboost condition can lead to poor performance and potential damage to the turbocharger. The vehicle may also enter a protective limp mode that severely limits speed and acceleration.
Common symptoms
- Illuminated Check Engine Light
- Noticeable lack of engine power or sluggish acceleration
- Vehicle entering limp mode (reduced power mode)
- Unusual whining or hissing noises from the turbocharger or intake
- Decreased fuel economy
Likely causes
- Boost leak in the intake tract, intercooler, or charge pipes
- Faulty or sticking wastegate or bypass valve
- Defective boost pressure sensor (MAP/TCBP)
- Vacuum leak affecting the wastegate actuator control
- Damaged turbocharger or supercharger internal components
- Restricted exhaust system (e.g., clogged catalytic converter)
What to check before replacing parts
Perform a visual and smoke test of the intake and charge pipe system.
Look for: Look for escaping smoke or obvious cracks, loose clamps, or disconnected hoses that indicate a boost leak.
Inspect the wastegate actuator and linkage.
Look for: Check if the linkage is disconnected, binding, or if the actuator fails to hold vacuum or pressure when tested with a hand pump.
Check the boost pressure sensor readings using a scan tool.
Look for: Compare the sensor reading with the engine off to atmospheric pressure; they should match. While driving, verify if the sensor registers appropriate changes in pressure.
Inspect the turbocharger compressor and turbine wheels.
Look for: Remove the intake boot and look for excessive shaft play, damaged fins, or oil pooling which indicates internal turbo failure.
Test for exhaust backpressure.
Look for: Install a pressure gauge in the upstream oxygen sensor port; high backpressure indicates a restricted exhaust or clogged catalytic converter preventing the turbo from spooling.
This page explains the generic P0299 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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