If you have diesel car with 5-cylinder engine from 2012 or newer, or you have 4-cylinder VEA engine, then you need to clean the boost pressure sensor every 30-80.000-km. Otherwise your engine power will rapidly decrease and you can expect the engine DTCs according the boost pressure.
You need to locate this sensor under the plastic cover. If you stand front of the car, you will have it in right bottom corner under the cover (same place for VEA and old 5-cyl. engine)
Unscrew the TX27 or TX30 screw and remove the sensor. The engine must be off and ignition key removed from ignition!
When you remove it, you will see somethign like this:
You need to scratch this mess off with needle or small flat screwdriver, but be really carefull and dont use too much power!
Once your work is done, you will see something like this:
And the sensor should look like this:
here inside are small holes - you need to clean them also! You can clean it with petrol or alcohol.
Once you finish, you can put it back and you can also reset the adaptation data for ECM - recommended.