When I start up the Car Manager I get this error:
Sep() failed!: [string “…”]:240: attempt to index field
‘FrontSuspensionLeft’ (a nil value)
Engine manager works perfectly
Some help please 
Have you installed some of the Mods like the Chrome Grilles Mod?
Anyways: I would try to reinstall the whole game. I had a similar bug, because of my small body modification. Reinstalling helped.
Thanks mate it helped. Good luck testing 