Code Definition

U2104 — Lost Communication With Engine Control Module (ECM)

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

About U2104

U2104 is a generic (obd-ii standard) network communication diagnostic trouble code recorded for Holden vehicles. 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 U2104 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

Module to module communication on this Holden uses a serial data bus (Class 2 or GMLAN depending on the model) so that controllers such as the BCM, ABS, instrument cluster, and ECM can share information. DTC U2104 is stored by a receiving module when it stops receiving valid serial data messages from the Engine Control Module within a calibrated time window while the ignition is on. This means the ECM is either unpowered, has lost its ground, is internally failed and not transmitting, or the data circuit between the modules has been broken or shorted. Because so many systems depend on engine d...

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