Here you go Dave, All you ever wanted to know about the TVS.
Five Frequently Asked Questions about System Level Transient Voltage Protection
Near the end of the document they discuss the placement of the TVS. Any time you have inductance between the item being protected and the TVS, the item being protected will receive a higher voltage spike. You can't assume that all the voltage spikes come from the TIU channel and transformer, they can come from any inductance anywhere on the layout that suddenly loses power and has a collapsing magnetic field. Many accessories have coils that activate motion, when you de-energize the coil you have the potential to generate a voltage spike. If the engine is next to that accessory and some distance from the TIU (and it's TVS), your protection is substandard due to the inductance posted by the track and wire between the engine and the TIU TVS.
Will this be an issue? Maybe not. However, if there was no reason to have TVS protection, why is it in the TIU?
