What is OBD-II Code P0299 – Turbocharger/Supercharger A Underboost Condition

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What is OBD-II Code P0299 – Turbocharger/Supercharger A Underboost Condition

OBD-II codes are diagnostic trouble codes that serve as a standardized language for vehicles to communicate with mechanics and technicians. These codes provide essential information about the health and performance of key components, such as the engine, transmission, and emissions systems, and help diagnose and repair issues more efficiently and accurately. OBD-II Code P0299 is one of the most common codes related to turbochargers and superchargers, which are devices that compress more air into the engine and increase its power output. In this article, we will explore in-depth what OBD-II Code P0299 means, what causes it, and how to fix it, from the perspective of a mechanic who has seen these problems firsthand.

Caution: This article is for educational and informational purposes only. It is not intended to be a substitute for professional advice, diagnosis, or repair. Always consult a qualified mechanic or technician before attempting any repairs on your vehicle.

Symptoms of OBD-II Code P0299
As with many OBD-II codes, OBD-II Code P0299 can trigger several symptoms that may indicate that there is a problem with the turbocharger or supercharger system. Some of the most common symptoms are:

1. A decrease in power or acceleration
2. A whistling, hissing, or sucking sound from the engine
3. A lack of boost pressure or pressure control
4. A rough or unstable idle
5. A blinking or illuminated check engine light (CEL)
6. A reduced fuel economy or efficiency
7. A reduced top speed or hauling capacity

These symptoms can vary in severity and frequency depending on the specific make, model, and year of the vehicle, as well as the driving conditions and habits of the owner or operator. For example, a turbocharged diesel pickup truck may exhibit different symptoms than a supercharged sports car. Therefore, it is essential to diagnose the root cause of OBD-II Code P0299 before attempting any repairs.

Causes of OBD-II Code P0299
OBD-II Code P0299 indicates that the engine control module (ECM) has detected an underboost condition in the turbocharger or supercharger system. This means that the actual amount of boost pressure is lower than the expected amount, which may cause the symptoms mentioned above. An underboost condition can be caused by several factors, including:

1. A malfunctioning wastegate valve or actuator: The wastegate is a mechanical valve that regulates the exhaust flow from the turbine side of a turbocharger. If the wastegate valve or actuator fails, it can either stay open, leading to lower boost pressure, or stay closed, leading to higher boost pressure.
2. A clogged, leaking, or damaged intake or exhaust system: The air intake and exhaust systems of a turbocharged or supercharged engine must be free of restrictions or leaks to ensure proper airflow and exhaust. Any blockage or damage can disrupt the pressure balance and cause an underboost condition.
3. A faulty boost pressure sensor or circuit: The boost pressure sensor or circuit measures the actual boost pressure and sends this information to the ECM for comparison with the expected boost pressure. If the sensor or circuit fails, it can either report a false high or low reading, leading to incorrect fuel and timing settings.
4. A dirty or failing turbocharger or supercharger: The turbocharger or supercharger itself may become clogged or worn over time, reducing its efficiency and output. This may be more common in engines that are frequently operated in harsh or dusty environments or that are not properly maintained.
5. A software or programming error: The ECM that controls the turbocharger or supercharger system may have a bug, glitch, or outdated software version that causes it to misinterpret the boost pressure signal. This is less common but still possible, especially in older or non-OEM ECUs.

Diagnosis and Repair of OBD-II Code P0299
Diagnosing and repairing OBD-II Code P0299 can vary in complexity and cost depending on the cause and extent of the issue. The first step is to retrieve and read the code with an OBD-II scanner, which can provide additional data about the timing, frequency, and other parameters of the underboost condition. Once you have verified the code and with the symptoms, the next step is to inspect and test the relevant components of the turbocharger or supercharger system using diagnostic tools, such as a boost pressure gauge, a multimeter, or a smoke tester. You may need to consult the vehicle’s repair manual or online resources for the specific procedures and specifications.

Some possible repair options for OBD-II Code P0299 are:

1. Replace or repair the wastegate valve or actuator if found faulty.
2. Clean, fix or replace the intake and exhaust systems if found dirty, damaged or clogged.
3. Replace or reprogram the boost pressure sensor or circuit if found faulty.
4. Replace or overhaul the turbocharger or supercharger if found dirty, worn or damaged.
5. Update or reflash the ECM software or firmware if deemed necessary or recommended by the manufacturer.

The cost of such repairs can range from a few hundred dollars to several thousands depending on the complexity and labor involved. It is advisable to obtain multiple quotes and recommendations from reputable shops or dealerships before deciding on a course of action. It is also essential to ensure that the parts and services that you use are of high-quality and compatible with your vehicle to avoid further issues down the road.


1. What is a turbocharger or supercharger, and how does it work?

A turbocharger or supercharger is a device that compresses more air into the engine than it would naturally aspirate, which increases the oxygen content and allows for more fuel to be burned, resulting in more power output. A turbocharger uses a turbine that is driven by the exhaust gases to spin a compressor that compresses the intake air, while a supercharger uses a belt or a gear to spin the compressor directly off the engine’s crankshaft.

2. Is it safe to continue driving with OBD-II Code P0299?

It is not recommended to continue driving with OBD-II Code P0299 as it may lead to reduced performance, increased emissions, and potentially more severe engine damage if left unchecked for long periods. Moreover, a blinking or illuminated CEL may trigger other OBD-II codes that can further complicate the diagnosis and repair process.

3. Can I fix OBD-II Code P0299 by simply resetting the ECM?

Resetting or clearing the ECM’s memory may temporarily remove the OBD-II Code P0299, but it will not fix the underlying issue that caused it. Moreover, it may erase other valuable diagnostic data that can help diagnose the issue more accurately later. Therefore, it is not recommended to reset the ECM as a permanent solution.

4. Can I drive without a working turbocharger or supercharger?

It is possible to drive without a working turbocharger or supercharger, but it may result in reduced performance, poorer fuel economy, and increased emissions. In some cases, it may also lead to more severe engine damage if the engine is pushed too hard or operated under stressful conditions.

5. How can I prevent OBD-II Code P0299 from occurring again?

To prevent OBD-II Code P0299 from occurring again, you can follow some basic maintenance and driving practices, such as:

1. Checking and replacing the air filter regularly to ensure proper airflow.
2. Checking and replacing the oil and oil filter regularly to avoid clogs and wear.
3. Using high-quality fuel and additives to prevent deposits and corrosion.
4. Avoiding harsh driving habits that may stress the engine, such as sudden accelerations, constant idling, or racing.
5. Consulting the vehicle’s owner’s manual or repair manual for specific maintenance recommendations and schedules.

Note: Always talk to a trusted mechanic or dealership for personalized advice and expertise tailored to your vehicle and driving habits.

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