SQ8 P0299 Turbo under boost. Build boost very slowly.

**Cash1333** · 04-15-2025 06:53 AM

Quick story, I bought a 2020 SQ8 about 6-7 months ago, and things were fine. Then one day, I randomly got a P0299 code and started inspecting the wastegate; there were no raddles or anything, but then I noticed that the coolant was a little low. So replaced the thermostat and water pump and vacuum lines, and O rings, etc. The car drove fine for another 800 miles before again getting the P0299 code. I used my Autel to move the DV actuators manually, and that worked as normal. I drove it around to water to see if one turbo was making more boost than the other, but it was making the same and going up at the same time. The boost would only go up to about 1/2 on the boost chart and go slowly. When replacing the vacuum hose, we checked and there was no coolant inside of it, as the issue was the outside housing of the water pump O-ring was leaking. Does anyone have any suggestions on what it could be? Could it be the N75 valve?

**CYANiD3** · 04-19-2025 07:35 PM

I think I've seen your post on the facebook groups. I'd do the solenoid valve block off (check youtube, someone posted a video on an SQ7). That's basically free. If that fails, I'd replace that entire solenoid assembly. I only mention this because I'm not sure you replaced that during your water pump replacement and that seems to be a standard item that is replaced at the dealer when doing the water pump.