The error "GPU fell off bus" is a critical failure where the PCIe link between the GPU and the CPU/PCIe Switch has collapsed, often due to thermal stress, power instability, or physical hardware defects. To isolate the root cause during an intensive workload like NVIDIA NeMo (Large Language Model framework), the administrator must collect high-fidelity telemetry.DCGM (Data Center GPU Manager)diagnostics are designed for exactly this scenario. By running dcgmi diag -r 3 (a comprehensive hardware stress test) or monitoring health via dcgmi health --check concurrently with the workload, the system can capture the exact moment parameters like PCIe replay counts, temperature spikes, or XID errors occur. This data allows the engineer to determine if a specific H100 module is faulty or if the issue is systemic (e.g., a failing PCIe switch on the motherboard). Lowering the workload (Option C or D) might hide the symptom, but it does not diagnose the hardware's inability to handle peak power and data throughput.