When performing a Land Rover Discovery Ls Swap, encountering communication problems between the engine control module (ECM) and transmission control module (TCM) can be frustrating. A common issue is the U0100 code – Lost Communication with ECM/PCM, often accompanied by a no-start condition. This article will delve into diagnosing and resolving these CAN bus communication issues.
One of the primary challenges with aftermarket wiring harnesses, like those from PSI Conversions, is the lack of detailed CAN bus wiring diagrams. Understanding the specific CAN layout is crucial for effective troubleshooting. Unlike the factory “inline” CAN bus configuration, aftermarket harnesses may utilize a “wye” or “tee” design with different terminating resistor setups. This variance makes generic diagnostic tips unreliable.
To pinpoint the problem, you need to trace the CAN bus wires and create your own wiring diagram. This involves identifying the correct pin connections for the ECM and TCM within the PSI harness. While tedious, this process is essential for accurate diagnosis.
A practical starting point is to test communication by unplugging each module individually. First, disconnect the ECM and attempt to read the TCM’s tune. If the TCM still responds, the circuit might be a “wye” configuration. Conversely, if disconnecting the TCM results in losing communication with both modules, it suggests an “inline” setup similar to the factory harness.
While PSI Conversions should ideally provide a CAN bus diagram, you can try contacting their support for assistance. Their expertise might offer valuable insights into their specific harness design.
Although a U0100 code might not directly cause a no-start, certain electronic throttle control (ETC) faults, influenced by the TCM, can intentionally prevent starting for safety reasons. Therefore, resolving the communication issue is vital.
Interestingly, the absence of a corresponding U0101 code (No Communication with TCM) in the ECM raises questions. Typically, a no-communication issue would trigger codes in both modules. This anomaly adds another layer to the diagnostic process. Further investigation might involve checking for other U codes in the TCM related to modules like the ABS and BCM, even if they are set to “No MIL Light.” Additionally, verify if the catalyst test remains enabled.
