OBD-II Code P0299 — What It Means & How to Fix It

What Does This Error Mean?

P0299 means the PCM detected that boost pressure is lower than expected — called underboost. This applies to both turbocharged and supercharged engines. The engine is not making as much power as it should under load. Common causes include boost leaks, a failing turbo, or a faulty wastegate.

Affected Models

All 1996+ turbocharged and supercharged vehicles
Very common in Ford EcoBoost engines (1.5T, 2.0T, 3.5TT)
Common in Subaru turbocharged WRX, STI, and Forester XT
Common in VW/Audi 1.8T and 2.0T engines
Common in GM trucks with the 2.7T and 3.0 diesel engines

Common Causes

Boost leak from a cracked intercooler pipe, loose hose clamp, or split coupler hose
Stuck-open wastegate allowing boost to bleed off before reaching target pressure
Worn or damaged turbocharger with reduced compressor efficiency
Faulty wastegate control solenoid not holding the wastegate closed properly
Failed boost pressure sensor giving the PCM incorrect low-boost readings

How to Fix It

Perform a visual inspection of all intercooler pipes, hoses, and couplers between the turbo and the intake manifold. Look for cracks, splits, or hose clamps that have come loose. Squeeze rubber couplers to feel for soft spots or cracks.

Boost leaks are the most common cause of P0299. A small crack in a coupler hose is easy to miss but causes a significant boost loss.
Perform a pressurized boost leak test if available. This involves blocking off the intake and pressurizing the charged air system with compressed air. You will hear or feel any leaks. This is far more effective than a visual check alone.

DIY boost leak testers are available online for under $30. Many specialty auto parts stores will also lend them. This tool pays for itself quickly on turbocharged vehicles.
Check the wastegate actuator and solenoid. On external wastegates, check that the actuator rod moves freely. On electronic solenoid-controlled wastegates, test the solenoid resistance and check for fault codes specifically for the solenoid circuit.

A stuck-open wastegate lets exhaust bypass the turbo, preventing the turbo from spinning fast enough to build target boost pressure.
Check turbocharger shaft play with the engine off and cooled down. Reach into the air intake and grasp the compressor wheel. Radial (side-to-side) play should be minimal. Excessive play indicates bearing wear — the turbo may need replacement.

Some axial (in-and-out) play in the shaft is normal. Significant radial wobble is a sign of worn bearings and reduced compressor efficiency.
Verify the boost pressure sensor is working correctly using live scan data. At idle it should read near atmospheric pressure. Under full-throttle acceleration it should climb to the vehicle's specified boost target. A sensor stuck at a low value can cause a false P0299.

Compare boost sensor readings to a known-good vehicle of the same model if you can. Alternatively, a technician can verify sensor accuracy with a calibrated pressure gauge.

When to Call a Professional

A boost leak test using a pressure-testing kit is the best starting point. If no leaks are found, the turbo, wastegate, or solenoid needs further testing. A shop can perform a full turbo health check including shaft play measurement. Diagnosis typically runs $100-$150. Repairs range from $20 for a hose clamp to $1,500+ for turbo replacement.

Frequently Asked Questions

How serious is P0299?

It is moderately serious. Your engine is not producing the power it should. This means you may lack power when merging onto a highway or passing. In most cases the vehicle goes into reduced power mode to protect the engine. Drive gently and get it diagnosed soon.

Can a boost leak really cause this code?

Yes — boost leaks are the number-one cause of P0299. Even a small leak in an intercooler coupler drops system pressure. The PCM sees lower boost than commanded and sets the underboost code. Always check for leaks before replacing expensive parts like the turbo.

Does P0299 mean my turbo is dying?

Not necessarily. A failing turbo is one possible cause, but it is not the most common one. Boost leaks, a faulty solenoid, and a stuck wastegate are all more likely. Check all of those first. Turbo diagnosis should be a last step after simpler causes are ruled out.