The controller area network (CAN) is a field bus that has been widely used in distributed embedded systems due to its inexpensiveness, robustness, guarantee of latency times as well as error detection. However, electromagnetic interference from the operational environment and hardware malfunction may cause short disturbances and permanent failures respectively, inevitably bring on communication errors or even break off the communication. To enhance the dependability of CAN communication, research on the on-line fault diagnosis is carried out in this paper, a Monitor is designed to diagnose faults in CAN nodes and a hybrid method with active and passive mode is presented to diagnose faults among communication links. We analyze the relative works, describe the CAN fault model, and focus on the fault diagnosis mechanisms.