Techniques for diagnosing lead fractures and lead connection problems are described. One or more medical leads may be coupled to an implantable medical device (IMD) to position electrodes or other sensors at different locations within a patient than the IMD. The IMD may include a lead diagnostic module configured to diagnose problems with a coupled lead and automatically select between a lead fracture problem and a lead connection problem based on the diagnosis. The diagnosis of either lead fracture problems or lead connection problems may be based on a timing of an increased impedance value with respect to connection of the lead to the IMD, a return to baseline impedance values after the increased impedance value, an abrupt rise of the increased impedance value, maximum impedance values, or oversensing. An external device may present the diagnosis to a user to facilitate appropriate corrective action.
