External leak on intake or exhaust side
Faulty Charge Air Pressure Sensor
Faulty Wastegate Regulator Valve
Engine Light ON (or Service Engine Soon Warning Light)
Charge Pressure Negative Deviation is the generic description for the P1556 Audi code, but the manufacturer may have a different description for your model and year vehicle. Currently, we have no further information
about the P1556 Audi OBDII code.