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This is a common code if you search.
VAG Error Code: 17965
EOBD II Error Code: P1557
Fault Location:
Charge Pressure Control - Positive deviation
Possible Cause:
Reduced power output.
Limp mode.
Boost Pressure too High.
Hoses/Pipes incorrectly connected, disconnected, blocked or leaking.
Charger Pressure Control defective.
Variable Nozzle Turbo (VNT) nozzles stuck.
Solenoid Valve for Boost Pressure Control (N75) defective.
Possible Solutions:
Check Hoses/Pipes to/between Components.
Check Solenoid Valve for Boost Pressure Control (N75).
Check / Clean / Replace Charge Pressure Control.
Check / Clean mechanism for variable nozzles.
As taken from my
Free EOBD II Error Codes software