DTC U2105: Lost Communication With Engine Control Module (ECM): 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 bus 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 once ignition switch is turned to ON position. The TCM and EBTCM monitor received messages from ECM for corruption or missing messages. DTC U2105 will be set if TCM and/or EBTCM does not receive a message back from ECM 3 seconds after initialization, or if the message is corrupted. If TCM sets DTC U2105, SERVICE TRANSMISSION light will be illuminated, request is sent to ECM to illuminate the SERVICE ENGINE SOON light on the second consecutive drive cycle that the diagnostics run and fail, and transmission will be placed in default mode (maximum line pressure, 4th gear commanded, TCC inhibited and freeze shift adapts). If EBTCM sets DTC U2105, a malfunction DTC is stored, traction control system is disabled, and traction control indicator light will be illuminated.

A current DTC U2105 in TCM will clear when conditions for setting DTC are no longer present (TCM will turn off SERVICE TRANSMISSION light and ECM will turn off CHECK ENGINE SOON light after 3 consecutive drive cycles that TCM does not send a MIL request), or a scan tool is used to clear DTCs. A history DTC U2105 in TCM will clear after 40 consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission-related diagnostic. TCM will cancel default mode of transmission when conditions no longer exist and ignition switch is off long enough to power down TCM.

A current DTC U2105 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 U2105 in EBTCM will clear after 100 consecutive warm-up cycles with no malfunction detected.