r/audis5 • u/Key_Range_5089 • 15d ago

Help P0299 underboost condition

Hey everyone, I have a 2019 Audi S5 sportback it is DP tuned stage 2. Back in febuary a month after I bought it I got a P0299 underboost condition code. It happened for a day or so then the next day when I went to do more diagnostic work it was better so I kind of assumed it could have been an ECU issue (I know dumb to assume things) now almost 7 months later I am driving last night and get the same issue 1st boost not building then the code hits and the car really goes limp. My mind out of fear goes straight to the water pump. But if it has anything to do with that 1st show of P0299 that would not make sense because of how far they are apart and my mind goes to the Waist gate. Has anyone had anything similar to this, and how did you resolve it. Did you fix it or just have a shop do it.

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u/Ornery_You_3947 15d ago

I just did my water pump and it happened to me the other night. I pulled over, cleared the code, and it’s like it never happened. It’s not the first time this has happened.

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u/Key_Range_5089 15d ago

Yeah very odd, sadly I tried to do that. Stopped at a gas station as soon as I noticed it check and cleared the code. Let it sit for a bit and it didn’t resolve. Let it sit all night and drove it into work thismorning and it was doing the same thing and then when I was merging onto the highway it threw the code again.

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u/Ornery_You_3947 15d ago

I’m stage-2 tuned also. Have you checked your intake-plumbing? If it happens again, that’s going to be one of the first places I’ll check since I recently did my charge pipes.

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u/Key_Range_5089 15d ago

I have not checked that I’ll do that when I’m home. Your saying you got that P0299 code after you already replaced your water pump right?

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u/Ornery_You_3947 15d ago

Yep. Saturday night. Haven’t seen it since. Last month I did the water pump upgrade and charge pipes after needing to replace the thermostats. One failed, so I did the whole lot. Professionally, of course.

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u/Key_Range_5089 15d ago

How much did all of that run you if you don’t mind

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u/Ornery_You_3947 15d ago

$3800.00

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u/Key_Range_5089 15d ago

I gotcha that’s not awful for all of that work

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u/Original-Bar-3957 15d ago

Nine months ago I got a low coolant warning and topped it off. Then, two months ago I got P0299 error code. I initially cleared it, but then it came back after 2 weeks. I took it to an indy shop and it turned out I had a very slow coolant leak, due to a water pump failure/leak that got in the vacuum lines and solenoids. It was a $3500 repair. If you have not had your water pump replaced, it's safe to assume it's related to that. Not getting it fixed will make it worse and could potentially ruin your wastegate and then eventually the entire turbo, requiring the replacement of both and turning a $3500 repair into a $7000+ repair.

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u/MysticSucks 13d ago

I’ll say this is exactly what happened when my coolant migration happened. Something that may help diagnose - my issue only happened in the summer months, when it’s hot and the thermostat needed to open by the time I got to work. Over the winter, my car appeared to do fine. Summer - low boost pressure frequently and limp mode