In automotive industry the role of electronic system becomes phenomenal. The complexity of the system increases to a larger extend now a days, and hence the diagnostics is also very much essential. The diagnostics can be mainly done in sensors/actuators, processors and on communication medium. Here, we have presented a fault detection system using fuzzy logic for the CAN (Controller Area Network). Whenever a fault occurred in the CAN, a Diagnostic Trouble Code (DTC) corresponding to that fault is recorded in an ECU (Electronic Controlled Unit) which is capable of detecting distinct faults only. In this paper we have proposed a prototype of an ECU using MicroAutoBox — II hardware, with a CAN interface to detect faults induced into the network. Fuzzy engine within the ECU is capable of identifying the faults based on the number of error frames (Ef), ranges from 0–80 as well as change in differential bus resistance (Rdiff(total)). The validation is done based on the rule created in the fuzzy system.