GM Technical Service Bulletin #77-63-06Ab states that: "stalling, hard starting, and hesitation are symptoms of a failing PMD (Pump Mounted Driver) module." These symptoms usually (but not always) set a code 35 or 36 in the 1994 - 1995 models, or a code 1216 in the 1996 - up models. Often when this problem is diagnosed at a dealership or repair shop, the customer is told that the injection pump needs to be replaced. But in most cases, the PMD module can simply be replaced for a fraction of the price. This unit is the latest design used by GM and replaces the 34583 and the 35976 previous models.