The current study investigates colesevelam as add-on therapy to pioglitazone to improve glycemic control in subjects with type 2 diabetes mellitus not adequately controlled with pioglitazone monotherapy or pioglitazone in combination with either metformin or a sulfonylurea. The study will evaluate if colesevelam add-on to pioglitazone therapy for type 2 diabetes mellitus will be safe, well tolerated, and efficacious.