#OBD Codes
P0299 – Turbocharger/Supercharger underboost condition
Technical definition
Turbo/Super charger underboost
What does P0299 mean?
The P0299 diagnostic trouble code (DTC) shows up when your car's engine isn't getting enough boost from the turbocharger or supercharger. This means the boost pressure going into the engine is lower than what the engine control unit (ECU) requires.
This fault only occurs on forced-induction engines. These engines use a turbocharger or supercharger to push extra air into the engine – helping it burn fuel more efficiently and boosting power.
The image below shows how a turbocharged engine works. Exhaust gases spin a turbine that drives a compressor to force more air into the engine. This extra air, which is cooled before entering the engine, helps burn more fuel and increase power. The cycle repeats as the exhaust continues to spin the turbine.
A supercharger, on the other hand, is a more straightforward mechanism. Its compressor is driven by a belt connected to the engine. It pushes additional air directly into the intake without relying on the exhaust.
Simultaneously, the ECU calculates how much boost the engine needs at any given time and measures the actual boost pressure the turbocharger/supercharger provides. If the ECU notices that the air pressure is way too low for the engine to run smoothly, it will trigger code P0299.
For example, Ford vehicles show a P0299 code if the actual throttle intake pressure (TIP) is 4 psi or more below the desired level for at least 5 seconds.
Common causes of this problem include a faulty turbocharger or supercharger, restrictions in the air intake system, boost leak, faulty sensors, or even low oil pressure.
As a result, you might notice reduced engine power, a check engine light, or odd sounds from the engine, especially from the air intake.
How serious is P0299?
Code P0299 indicates a serious problem that requires immediate attention. If you're lucky enough to catch a turbocharger failure early, you may still have a chance to repair it without major expense.
However, ignoring the issue can cause irreversible damage, not just to the turbocharger or supercharger but also to the engine itself.
Can I still drive with P0299?
Driving with a P0299 error code is possible but not recommended.
If you must, only drive to a nearby mechanic and proceed with caution. Keep engine speed low and avoid sudden throttle inputs to minimize potential engine damage.
The P0299 code significantly reduces engine power and can trigger limp mode. This limits your speed and makes it difficult to accelerate, potentially putting you in dangerous situations on the road.
Symptoms of P0299
Symptoms associated with the P0299 code include:
- Reduced engine power and acceleration
- Limp mode
- Sluggish response, especially when trying to speed up
- Reduced gas mileage
- Whining or hissing noises from the turbocharger
- Check engine light is on
- Rough idling or possible stalling
- Difficulty reaching high speeds, especially under load
Common causes of P0299
- Faulty diverter valve: The diverter valve controls the release of excess boost pressure. If it malfunctions, it can cause a loss of boost pressure. This is one of the most common causes of P0299, but it is relatively easy to fix.
- Dirty air filter or clogged intercooler: Another very common problem is restrictions in the air intake system, which can block airflow into the engine and prevent the turbocharger from building up proper boost pressure.
- Issues with turbocharger or supercharger: Problems with turbocharger or supercharger parts can reduce efficiency and are among the most serious and costly causes of P0299.
- Bad wastegate bypass regulator valve: This valve controls the turbocharger's boost pressure. If the wastegate gets stuck in the open position, the turbo can't build up a boost.
- Air intake leak: Leaks in the air intake system after the turbo can also cause pressure loss.
- Vacuum leak: Some cars use a vacuum to control the wastegate, so a leak can interfere with wastegate operation. It can also cause inaccurate mass airflow (MAF) sensor readings, which lead the ECU to miscalculate air intake.
- Clogged catalytic converter: A clogged catalytic converter can create excessive backpressure in the exhaust system, hindering the turbocharger's ability to build a boost.
- Faulty sensors: Issues with the manifold absolute pressure (MAP) sensor or boost pressure sensor can lead to incorrect readings and improper boost management by the ECU.
- Wiring circuit issues: Damaged wires or poor connections in the boost control circuit can disrupt communication between sensors and the ECU.
How to troubleshoot P0299
Use these tips to diagnose and fix a P0299 code accurately:
Check the air intake filter condition
Open the hood, locate the air filter, and check its condition. If it's dirty, replace it. This is one of the easiest and cheapest ways to fix a P0299 code.
Scan for other codes
Use an OBD scan tool to check for other DTCs that may provide additional clues to the underlying problem. These include:
P2262: If you see this code along with P0299, it likely means a mechanical problem with the turbocharger itself, such as a stuck wastegate, faulty boost sensor, or clogged intercooler.
P0243-P0250: These codes indicate problems with the wastegate solenoid, which regulates the turbocharger’s boost pressure. A faulty solenoid can cause either underboost or overboost, affecting engine performance.
P0235-P0242: These codes indicate a malfunction in the boost sensor circuit. If you see these codes, check the turbocharger boost sensor, wiring, and connectors, as incorrect sensor data can result in underboost conditions, where the engine doesn't receive enough pressure from the turbocharger or supercharger.
Clear the codes and test drive
Use your scanner to clear fault codes. If the fault codes persist, it confirms the issue is ongoing, and you should skip the following test drive part.
Then, drive your car for about 15 minutes to fully warm up the engine. Also, try driving at different engine speeds, as sometimes this code only shows up at high RPMs.
After the drive, perform another scan to see if the issue reappears. If it does, it's an ongoing failure that requires further investigation to fix.
Check freeze frame data
The freeze frame data captured when the fault code occurs can provide valuable insight. This may include mileage, date, engine load, temperature, rpm, and other parameters that help you understand the conditions that triggered the code.
For example, you can use the date or mileage data to recall the driving conditions – whether it was highway, city, track driving, or a day with extreme weather, like unusually hot or cold temperatures. These clues can help the technician find the root cause of the problem.
Compare specified boost pressure to actual boost pressure
To better understand the severity and persistence of the issue, compare specified boost pressure to actual boost pressure live data readings.
Specified boost pressure is the target pressure calculated by the ECU. It depends on engine conditions, such as throttle position, engine load, and speed.
Actual boost pressure is the real pressure measured by the sensor in the intake manifold. It shows what the engine is actually experiencing at any given time.
In some cars, these values are labeled as charge pressure instead of boost pressure.
In the OBDeleven VAG mobile app, you can find boost pressure readings under the engine control unit details.
OBDeleven live data feature
If you're using an Android device, that's even better. You can log live data values in a chart, which makes comparing them much easier.
OBDeleven charts feature
In theory, the specified and actual boost pressure lines should match closely. However, it's common for the actual value to be slightly lower or higher, and it takes a moment to catch up. This delay is known as turbo lag and shouldn't last more than five seconds.
The specified/actual boost pressure chart should look similarly this:
Actual (blue) and specified (green) boost pressure in normal conditions
In the underboost condition, you should notice that the actual pressure is much lower than the specified pressure. You may also see long lags.
In this case, the specified/actual boost pressure graph may look like this:
Actual (blue) and specified (green) boost pressure in underboost conditions
Inspect vacuum hoses
Start by looking for cracks, holes, or disconnected vacuum hoses and replace any damaged ones.
For a more thorough check, try a smoke machine test. This method fills the system with smoke, which escapes from any cracks, holes, or loose connections, making it easy to pinpoint the exact location of a leak.
How much does it cost to fix the P0299 code?
Fixing a P0299 code can cost from as little as fifty dollars for a new diverter valve or air filter to several thousand dollars for a new turbocharger/supercharger or engine itself.
Disclaimer: Advice, how-to guides, and car care tips on our blog are intended as helpful resources for general maintenance and repairs. While we strive for accuracy, the information is provided to the best of our knowledge and should be used at your own discretion and risk.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.
Always refer to your vehicle's owner's manual or consult a certified mechanic for specific repair details and safety procedures.