P0299
UniversalThe Powertrain Control Module (PCM) has detected that the actual boost pressure from the turbocharger or supercharger is below the manufacturer's specified range for a predetermined period of time.
Medium SeverityThis code indicates that your vehicle's turbocharger or supercharger is not generating the expected amount of boost pressure, leading to reduced engine performance. This underboost condition results in a noticeable lack of power and slower acceleration for the driver.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool down before working on any components. Disconnect the battery before performing electrical work. Use proper jack stands when lifting the vehicle. Components within the engine bay can be very hot, so wear appropriate protective gear.
Common Symptoms
- Reduced engine power or acceleration
- Check Engine Light illuminated
- Turbo lag or delayed boost response
- Whistling or hissing noises from the engine bay
- Engine entering "limp mode"
Common Causes
- Vacuum leak or boost leak (cracked hoses, loose clamps, damaged intercooler)
- Faulty wastegate actuator or sticky wastegate
- Malfunctioning turbocharger bypass valve or blow-off valve
- Clogged or restricted catalytic converter or exhaust system
- Faulty boost pressure sensor (MAP sensor)
- Damaged turbocharger compressor or turbine wheel
- Failed turbocharger itself
- Issues with the N75 valve (boost pressure control solenoid)
- PCV system issues leading to vacuum/boost leaks
Frequently reported on: Ford F-150 (2011-2016), Volkswagen Golf/Jetta TDI (2009-2014), Subaru WRX/STI (2008-2014), BMW 335i (E90/E92, 2007-2010), Audi A4 (B8, 2009-2012)
Diagnostic Steps
- Visually inspect all turbocharger/supercharger plumbing, vacuum lines, and intercooler for cracks, loose connections, or damage.
- Check the air filter and intake system for obstructions.
- Listen for whistling or hissing sounds during acceleration, which may indicate a boost leak.
- If accessible, inspect the wastegate actuator and its linkage for proper operation and freedom of movement.
- Use an OBD-II scanner to monitor live data, specifically boost pressure, MAF sensor readings, and O2 sensor readings, to identify discrepancies.
- Consider performing a smoke test to definitively locate boost/vacuum leaks.
- If equipped, check the proper function of the diverter valve/bypass valve.
👨🔧 When to Call a Professional
If you have checked for simple boost leaks and still cannot identify the cause, or if the issue involves internal turbocharger components, it is best to consult a professional mechanic specializing in forced induction systems.
Commonly Asked Questions
What is "underboost"?
Underboost means the turbocharger or supercharger is not generating the expected amount of air pressure (boost) that the engine needs for optimal performance.
Can I drive with a P0299 code?
While you can usually drive with P0299, it's not recommended for extended periods as it can lead to reduced power, increased fuel consumption, and potentially further damage to the turbo or engine components.
How can I check for a boost leak at home?
You can often hear a distinct hissing sound during acceleration if there's a significant boost leak. A more thorough method involves a smoke test, where smoke is introduced into the intake system to reveal leaks.
Is P0299 always a sign of a bad turbo?
Not necessarily. While a failing turbo is a possibility, P0299 is more often caused by simpler issues like boost leaks, a faulty wastegate actuator, a malfunctioning bypass valve, or a clogged exhaust.
What is the N75 valve's role in P0299?
The N75 valve (or boost pressure control solenoid) regulates the wastegate, controlling how much exhaust gas bypasses the turbo turbine. If it fails, it can prevent the wastegate from closing properly, leading to insufficient boost pressure.