Although it is possible to immobilize (ie. shut down) a vehicle using the IOX-RELAYKIT, Geotab does not sanction nor directly support using it for engine immobilization due to the the complex and wide variety of vehicle electronic and electrical circuits, and the fact that this solution is not fool-proof. You can find more detailed information on why this isn't supported at the following link: https://www.geotab.com/blog/immobilization-and-safety
Additionally, you can also read more about the application of the relay kit, and the other ways to make use of this powerful hardware add-in at the following link: https://docs.google.com/document/d/1j2TLZ1H9ah_PVxL7-mW0-VM_pv-YQlGouaZFnzrZAko/edit?usp=sharing
Please feel free to reach out if you have additional questions!