P0299: Turbo/Supercharger Underboost Condition

What is P0299?

Error code P0299 is a generic OBD-II Diagnostic Trouble Code (DTC) equipped to vehicles that have a turbocharger or supercharger. The code is defined as “Turbo Or Supercharger Underboost Condition.”

Your Engine Control Module (ECM) or Powertrain Control Module (PCM) looks for a specific range of boost (actual boost pressure) coming from your turbocharger or supercharger. They do this by monitoring the engine vacuum line (vacuum hose) and intake manifold pressure with a Manifold Absolute Pressure sensor (MAP sensor). 

When the boost control range detected by your ECM or PCM is too low, error code P0299 is set.

The difference between turbo and superchargers is how they’re driven, but P0299 refers to an underboost condition in both. 

Turbochargers are driven by the exhaust exiting the engine, and a turbine forces air into the intake. On the other hand, supercharges are mounted on the intake side and are typically belt-driven to force more air into the intake, with no connection to the exhaust.

Common symptoms

You may experience one or more of these common symptoms if you have an active P0299 error code:

• Illuminated Check Engine Light
• Decreased engine performance
• Limp mode activated
• Increased fuel consumption
• Marginal power difference when stepping on the accelerator pedal
• Mechanical noise (engine hissing or whining)

Note: Limp mode is a feature in modern cars triggered when your ECM or PCM detects a problem. Limp mode restricts your engine performance when the ECM or PCM senses conditions outside its normal control range.

Can I still drive?

Technically yes, but you should head to a professional mechanic ASAP to get an active P0299 code fixed.

Error code P0299 is not a code you should just ignore. If an active P0299 code isn’t repaired quickly, it could lead to severe engine damage and an expensive repair job.

P0299 causes

Here are some of the most common causes of error code P0299:

• A leaking or damaged charge pipe
• A failed diverter valve
• A defective boost pressure regulation valve
• A faulty fuel injection control pressure sensor
• A clogged air filter
• A faulty EGR system (Exhaust Gas Recirculation)
• Low oil pressure to the engine
• A failed turbocharger or supercharger
• A faulty boost pressure sensor
• A defective wastegate or wastegate actuator

Diagnosis

Here’s how a professional mechanic will diagnose the P0299 code:

• Your mechanic will use a scan tool to test for any other active error codes or fuel trim faults you may have alongside the P0299 DTC.
• Next, they’ll inspect each charge pipe for any leaks or damage. Boost leaks occur when pressurized air escapes the charge hoses after the turbo but before entering the engine. These hoses become damaged over time from normal wear and tear.
• Then, your mechanic will look at your diverter valve and inspect for a torn diaphragm — allowing pressurized air to leak.
• They’ll inspect your Mass Airflow sensor (MAF sensor) and air filter for any debris. A clogged air filter could significantly decrease your turbo or supercharger’s boost pressure.
• Your mechanic will inspect your boost pressure control valve for any damage. A damaged boost pressure control valve causes the wastegate lever to remain in an open position — preventing the vehicle from building any boost pressure.
• They’ll then inspect your turbocharger or supercharger for any damage. They’ll also look at the air intake system, oil pressure, EGR system, and each vacuum hose to see if there’s a vacuum leak.
• Your mechanic will look if you have a faulty boost pressure sensor that is not relaying the air intake system pressure reading to your Engine Control Module.
• Finally, they will inspect your wastegate actuator and actuator arm to see if they’re causing the underboost condition.

Possible repairs for P0299 & Costs

Since fault code P0299 has so many possible causes, your mechanic will need to entirely complete the diagnostic process before moving on to the repair job.

You don’t want to pay for a new turbocharger when your boost pressure sensor is the actual cause of the problem.

Here’s how a professional mechanic will fix error code P0299, depending on the problem:

• Other error codes: Your mechanic will fix any other active error codes you may have in order of seriousness.
• Charging pipe: A leaking or damaged charge pipe is a simple fix, and your mechanic will easily replace it for you if required.
• Diverter valve: If your diverter valve is faulty, your mechanic will replace it for you, and this should allow your engine to reach the desired boost pressure.
• Boost pressure control valve: If your boost pressure control valve is defective, your mechanic will replace it, allowing your vehicle to reach the desired boost pressure.
• Turbocharger or supercharger: If your turbocharger or supercharger is faulty, your mechanic can usually repair it for you. But your mechanic will replace the part if it’s damaged beyond repair.
• Boost pressure sensor: Your mechanic will look at your intake manifold where your boost pressure sensor is typically located and replace it if necessary.
• Wastegate actuator: If your wastegate actuator is damaged or if the wastegate diaphragm is worn out, your mechanic will replace these with new parts.