P0299: Turbo/Supercharger Underboost Condition
The P0299 code indicates that the engine control module (ECM) has detected that the boost pressure from the turbocharger or supercharger is lower than the expected value. This underboost condition can be caused by a variety of issues including boost leaks, faulty wastegate, clogged air filter, or a malfunctioning turbocharger. The ECM compares actual boost pressure (measured by the MAP or boost pressure sensor) to the desired boost pressure based on engine load and RPM. If the actual pressure is significantly lower, the code is set.
1. Most Common Causes
- Vacuum or boost pressure leak in intercooler/turbo system hoses
- Wastegate stuck open or faulty wastegate actuator
- Defective or leaking bypass/blow-off valve
- Worn or damaged turbocharger (impeller, shaft, bearings)
- Clogged or restricted air filter
- Obstruction in intake duct or intercooler
- Faulty or out-of-calibration MAP or boost pressure sensor
- Insufficient vacuum to wastegate actuator or failed N75/N249 solenoid
- Leak at intake or exhaust manifold gasket
- EGR valve stuck open (on applicable systems)
- ECM software needs update
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Loss of power or acceleration
- Whistling or hissing noise from engine bay
- Poor fuel economy
- Excessive black smoke from exhaust
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Visually inspect all boost hoses, intercooler, and intake for leaks or damage.
Step 3: Check the wastegate actuator and linkage for proper operation.
Step 4: Test the boost pressure sensor and MAP sensor with a multimeter or scan tool.
Step 5: Perform a boost leak test using a smoke machine or pressure tester.
Step 6: Inspect the turbocharger for shaft play, damage, or oil leaks.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with P0299 as it can cause reduced power and potential damage to the turbocharger or engine. Limp mode may activate, limiting speed. Have it diagnosed promptly.
How much does it cost to fix?▼
Cost varies widely depending on the cause. A simple boost leak repair may cost $50-$150, while turbocharger replacement can range from $1,000 to $3,000 or more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.