Code Definition

U0100 — Lost Communication with ECM/PCM 'A'

System: Network Communication  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About U0100

U0100 is a generic (obd-ii standard) network communication diagnostic trouble code. It belongs to the U-prefix family of codes, which covers inter-module network communication (CAN, LIN, FlexRay, or similar) faults.

Scanning & clearing: Network (U) codes report communication faults between modules. When diagnosing U-codes, checking the vehicle's CAN bus integrity, supply/ground at each module, and reading all modules for related faults is usually the first step.

Because U0100 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

Modern vehicles share information between control modules over a Controller Area Network (CAN) data bus, and the ECM or PCM broadcasts engine data such as engine speed, coolant temperature, throttle position, and calculated torque that many other modules depend on to do their own job. DTC U0100 is stored by a receiving module when the expected periodic messages from the ECM or PCM identified as module 'A' stop arriving, either failing to appear within a defined window after ignition on or dropping out during vehicle operation. It is important to understand that this code is a symptom reported ...

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