A method of failure-detection for a compressor inlet-adjustment mechanism disposed in an air inlet of a compressor of a turbocharger for boosting intake pressure of an internal combustion engine, the inlet-adjustment mechanism being actuatable to switch between a closed position that reduces a flow area of the air inlet and an open position that increases the flow area of the air inlet, the method comprising: identifying a threshold line on a compressor map specifying interrelationships between compressor pressure ratio PR, flow rate W, and one of turbocharger speed N and engine speed Ne, the threshold line being a line at which the inlet-adjustment mechanism is to be switched between the open position and the closed position when an operating point of the compressor on the compressor map reaches the threshold line; determining a measured compressor flow rate W m, a measured compressor pressure ratio PR m, and one of a measured turbocharger speed N m and a measured engine speed Ne m for a current operating point of the turbocharger and engine; determining a theoretical value for a characteristic compressor performance parameter for the current operating point, where is one of PR and N and where the theoretical value for is derived from a first compressor map MAPo specifying an interrelationship between flow rate W, pressure ratio PR, and one of turbocharger speed N and engine speed Ne, when the inlet-adjustment mechanism is open; determining whether the current operating point is on a high-flow side of the threshold line or is on a low-flow side of the threshold line; and when the current operating point is determined to be on the high-flow side of the threshold line at which a desired state of the inlet-adjustment mechanism is open, if a measured value for differs from the theoretical value for by more than a predetermined tolerance, determining that the inlet-adjustment mechanism is in a failure mode. identifying a threshold line on a compressor map specifying interrelationships between compressor pressure ratio PR, flow rate W, and one of turbocharger speed N and engine speed Ne, the threshold line being a line at which the inlet-adjustment mechanism is to be switched between the open position and the closed position when an operating point of the compressor on the compressor map reaches the threshold line; determining a measured compressor flow rate W m, a measured compressor pressure ratio PR m, and one of a measured turbocharger speed N m and a measured engine speed Ne m for a current operating point of the turbocharger and engine; determining a theoretical value for a characteristic compressor performance parameter for the current operating point, where is one of PR and N and where the theoretical value for is derived from a first compressor map MAPo specifying an interrelationship between flow rate W, pressure ratio PR, and one of turbocharger speed N and engine speed Ne, when the inlet-adjustment mechanism is open; determining whether the current operating point is on a high-flow side of the threshold line or is on a low-flow side of the threshold line; and when the current operating point is determined to be on the high-flow side of the threshold line at which a desired state of the inlet-adjustment mechanism is open, if a measured value for differs from the theoretical value for by more than a predetermined tolerance, determining that the inlet-adjustment mechanism is in a failure mode.