P0299: Turbocharger/Supercharger "A" Underboost Condition

What does P0299 mean?

On turbocharged and supercharged engines, the ECM compares the boost it wants with the boost pressure sensor reading. If actual boost stays below the target for too long, it stores P0299 and may limit power to protect the engine.

The "A" refers to the first or only turbocharger or supercharger. The code is common on both petrol and diesel engines, and the likely causes differ between engine types.

Common symptoms

• Check engine light on
• Noticeable loss of power, especially when accelerating
• Limp mode or reduced power warning on many vehicles
• Hissing or whooshing noise from a boost leak
• Black smoke on some diesel engines
• Higher fuel consumption

Common causes

The causes below are the ones commonly seen with P0299. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• Boost leaks from split hoses, loose clamps or a leaking intercooler
• A sticking wastegate or a faulty wastegate actuator
• Sticking variable geometry turbo vanes, often on diesels
• A faulty boost control solenoid or its vacuum lines
• A faulty boost pressure sensor or MAP sensor
• A restricted air filter or exhaust, including a blocked particulate filter on some diesels
• A worn turbocharger

What to check with a scanner

• Read all codes. Boost sensor or solenoid circuit codes can point to a specific part.
• In Live data, compare requested and actual boost (or MAP) if your vehicle provides both. A gap that grows with load fits a boost leak or turbo control problem.
• Check freeze frame data for rpm, load and boost when the code set.
• With the engine off, inspect intercooler hoses and clamps for oil residue or splits.

How to read and clear P0299 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0299 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0299 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0299.

When to see a mechanic

Get professional help if any of these apply:

• The car goes into limp mode repeatedly
• You hear a loud whistle or grinding from the turbo
• There is blue or heavy smoke, or oil in the intake pipes
• The code returns after fixing visible leaks

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Brand notes

Patterns below come from published manufacturer service information. They do not mean every vehicle of that brand has this problem, and a bulletin only applies to the vehicles it lists.

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