DTC U2104: Can Bus Reset Counter Overrun: 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. Each module on the CAN bus has a reset counter that tallies the number of times that module has tried to re-initialize communication on the CAN bus without success. The maximum number of attempts is 7. When module tries to re-initialize communication for the seventh time without success, DTC U2104 will be set. If ECM sets DTC U2104, SERVICE ENGINE SOON light will be illuminated on the second consecutive drive cycle that the diagnostics run and fail. If TCM sets DTC U2104, 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 U2104, a malfunction DTC is stored, traction control system is disabled, and traction control indicator light will be illuminated.

A current DTC U2104 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 U2104 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 U2104 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 U2104 in EBTCM will clear after 100 consecutive warm-up cycles with no malfunction detected.

A current DTC U2104 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 U2104 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.