Final answer:
If the ATS caution is on when a DDI comes on, it is important to shut down the affected engine to avoid starter damage.
Step-by-step explanation:
If the ATS (Automatic Transfer Switch) caution is on when a DDI (Diesel Direct Injection) comes on, it is important to shut down the affected engine to avoid starter damage. The reason for this is that the caution indicates a potential issue with the automatic transfer switch, which could affect the electrical system. By shutting down the engine, you prevent any further damage to the starter and ensure the safety and functionality of the system.