Lost Communication

📖 YOUCANIC Automotive Glossary

Lost Communication is a fault where modules cannot exchange data on the CAN Bus, generating U-codes identifying which module stopped communicating — U0100 (ECM), U0101 (TCM), U0121 (ABS), U0140 (BCM), U0151 (SRS). A single failed module or wiring fault can generate multiple U-codes across many modules simultaneously, creating a cascade that appears more complex than it is.

The diagnostic approach is identifying the common denominator. If U0100 appears in TCM, ABS, BCM, and SRS, all four report they lost communication with the ECM — the ECM or its CAN connection is the problem. Common causes: blown fuse, corroded connector, damaged CAN wiring, failed module, or gateway failure. The YOUCANIC UCAN-II Auto Scan reads all modules simultaneously, making it easy to identify which module is missing.