Enables mannosyl-oligosaccharide 1,2-alpha-mannosidase activity. Involved in positive regulation of retrograde protein transport, ER to cytosol and trimming of terminal mannose on C branch. Acts upstream of or within ubiquitin-dependent ERAD pathway. Is integral component of endoplasmic reticulum membrane. Is expressed in embryo and liver. Orthologous to human EDEM1 (ER degradation enhancing alpha-mannosidase like protein 1). [provided by Alliance of Genome Resources, Apr 2022]