Fault Phenomenon: Caterpillar 777G mining truck instrument displays “TCM Communications Lost,” transmission locked in neutral or a fixed gear.

Troubleshooting Process:
– Checked harness: TCM connector loose, water ingress, or harness worn.
– Checked power supply: TCM power fuse blown.
– Checked ground: ground wire poor contact.
– Checked module: TCM internally damaged.

Root Cause: The power line for the Transmission Control Module had poor contact due to vibration, causing the module to malfunction.

Required Parts: Repair wiring connections, replace TCM if damaged.