DTC U2103: Fewer Controllers On Bus Than Programmed: Description

Serial data on the CAN bus is transferred at a rate of 125 kilobytes-1 megabytes per second to ensure "real-time" response is maintained between Engine Control Module (ECM), Electronic Brake/Traction Control Module (EBTCM), and Transmission Control Module (TCM). When ignition switch is turned to ON position, modules begin to transmit data between each other. Each message sent on this data line has a unique identifier to classify the content and a priority assignment to denote importance. With this embedded information, only those modules on the CAN that have access to the message can receive the message. When more than one module on the network trys to transmit simultaneously, the message with highest priority gets access first.

The CAN bus circuit is continuously monitored by each module for activity or traffic once ignition switch is turned to ON position. The module that has set DTC U2103 has detected that there is no activity or traffic on the bus. This indicates there may be fewer controllers actively communicating on the bus than programmed. If ECM sets DTC U2103, SERVICE ENGINE SOON light will be illuminated on the second consecutive drive cycle that the diagnostics run and fail. If EBTCM sets DTC U2103, a malfunction DTC is stored, traction control system is not disabled, and traction control indicator light will not be illuminated.

A current DTC U2103 in ECM will clear when conditions for setting DTC are no longer present (ECM will turn off CHECK ENGINE SOON light after 3 consecutive drive cycles that the diagnostics run and pass), ECM battery voltage is interrupted, or a scan tool is used to clear DTCs. A history DTC U2103 in ECM will clear after 40 consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission-related diagnostic.

A current DTC U2103 in EBTCM will clear when conditions for setting DTC are no longer present, or a scan tool is used to clear DTCs. A history DTC U2103 in EBTCM will clear after 100 consecutive warm-up cycles with no malfunction detected.