Crash log-
https://gist.github.com/ProsperCraft/8924b6e6228abe3dc02fca293922eb25
java.lang.NullPointerException: Ticking entity at minecrafttransportsimulator.vehicles.parts.APartEngine.updatePart(APartEngine.java:235) at minecrafttransportsimulator.vehicles.parts.APartEngineGeared.updatePart(APartEngineGeared.java:19) at minecrafttransportsimulator.vehicles.parts.PartEngineCar.updatePart(PartEngineCar.java:18) at minecrafttransportsimulator.vehicles.main.EntityVehicleD_Moving.func_70030_z(EntityVehicleD_Moving.java:121) at minecrafttransportsimulator.vehicles.main.EntityVehicleE_Powered.func_70030_z(EntityVehicleE_Powered.java:64) at minecrafttransportsimulator.vehicles.main.EntityVehicleG_Car.func_70030_z(EntityVehicleG_Car.java:31)

I am told the vehicle is a -
Humvee with a V12 Turbit engine

Immersive Vehicles-1.12.2-16.0.0

Modpack - TownCraft 1 https://www.curseforge.com/minecraft/modpacks/towncraft/

While this was not fixed in V16.1.0, I did add debug information to the crash report that should tell you exactly what is wrong. I'm going to close this ticket, but if you can't figure out the issue from that information let me know and we can re-open this.