An injection molding machine for molding a multilayer article, comprising: a coinjection nozzle having a surface layer material channel (424, 428) and an internal layer material channel; a surface layer material injection unit; an internal layer material injection unit; a mold cavity; and a controller operable to: cause the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then cause the internal layer material injection unit to commence injecting an internal layer material into the mold cavity via the internal layer material channel; then during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure (P T). a coinjection nozzle having a surface layer material channel (424, 428) and an internal layer material channel; a surface layer material injection unit; an internal layer material injection unit; a mold cavity; and a controller operable to: cause the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then cause the internal layer material injection unit to commence injecting an internal layer material into the mold cavity via the internal layer material channel; then during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure (P T). cause the surface layer material injection unit to commence injecting a surface layer material into the mold cavity via the surface layer material channel; then cause the internal layer material injection unit to commence injecting an internal layer material into the mold cavity via the internal layer material channel; then during application by the surface layer material injection unit of a hold pressure upon the surface layer material in the surface layer material channel and with the surface layer material injection unit and the internal layer material injection unit in fluid communication with one another via the surface layer material channel and internal layer material channel, cause a pullback stroke to occur at the internal layer material injection unit for reducing a pressure of the internal layer material; then after a delay interval, detect at least one physical parameter indicative of a post-pullback pressure of the internal layer material at the internal layer material injection unit; and generate an indicator of pullback effectiveness based on a relationship of the post-pullback pressure indicated by the at least one physical parameter and a threshold pressure (P T).