2017 Audi A4 - P0299 Underboost Condition - Turbo or diverter valve?

Question

My B9 A4 just hit 85k miles and now it feels like it lost 50 horsepower. I'm getting a P0299 Underboost code. When I accelerate, I hear a faint whistling or whining noise that I didn't notice before.

I checked the intercooler hoses and they all seem tight. I don't see any obvious oil leaks around the turbo. Could it just be a simple sensor or am I looking at a full turbo replacement? I'm hoping it's not the wastegate rattle everyone talks about.

InternationalIan · Answer

Check the Diverter Valve (DV) on the side of the turbo. The older diaphragm-style ones rip all the time. On the B9, they should be the piston style, but they can still jam. It's a 3-bolt job and much cheaper than a turbo.

FreightlinerFred · Answer

✅ Confirmed fix: On the EA888 Gen 3 engine, the P0299 is frequently caused by a worn wastegate pivot arm. The arm gets loose where it enters the hot side of the turbo, preventing the wastegate flap from sealing fully.

I checked mine and could wiggle the arm by hand. I had to replace the entire turbocharger assembly since the wastegate housing isn't sold separately. If you can move the linkage and it rattles, the turbo is finished.

2017 Audi A4 - P0299 Underboost Condition - Turbo or diverter valve?

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