The crankshaft position sensor. Is it part of the engine or emistions system?

The crankshaft position sensor (CKP sensor) is part of the engine's system, not the emissions system. While its proper function is crucial for the engine's control system and therefore indirectly impacts emissions, its primary role is to tell the engine's computer (ECU) where the crankshaft is in its rotation cycle. This information is vital for ignition timing, fuel injection, and other engine functions.