At about 56,000 miles on my B6 Passat 2.0T , the CEL (Check Engine Light) came on, and when I scanned the car with VAG-COM, the following fault code was displayed:
000665 - Boost Pressure Regulation
P0299 - 002 - Control Range Not Reached
When I first bought the B6 Passat 2.0T, it really had power when the turbo kicked in, and now it felt like the engine was revving but you couldn't feel that power that pushed you back in your seat. After some research, I found the following information at ECS Tuning stating that when the 2.0T was introduced, one of the first failing points was the rubber diaphragm in the original diverter valve, even under stock boost pressure. When the seal fails, the boost escapes past the turbo, causing a large boost leak, which reduces performance. After many revisions the entire unit was redesigned, and "D" version was introduced, with a piston in place of the rubber diaphragm. This is a mechanical design that is more durable and is a great upgrade for all stock or modified 2.0T FSI & TSI engines.
The part number for the Diverter Valve is 06H145710DKT , and the OEM Upgraded Diverter Valve (ES#:263879) can be purchased online from ECS Tuning.
You can see the torn rubber diaphragm at the base of the stock Diverter Valve which is the green one on the left compared to the OEM Upgraded Diverter Valve on the right.
Replacing the Diverter Valve on the B6 VW Passat 2.0T is very simple. It is located behind the engine in front of the firewall, and you can access this part from under the car. An easy way to identify the Diverter Valve is that it is fastened by 3 silver Hex screws and it has an electric connector that plugs into it as displayed in the center of the image below.
Disconnect the electric connector first, and then unscrew the 3 silver Hex screws which will release the Diverter Valve part.