What is the crank sensor in Volvo 740 turbo 1989?

In a 1989 Volvo 740 Turbo, the crank sensor is a crucial component of the ignition system. It's a magnetic sensor that doesn't directly use a toothed wheel like some other vehicles. Instead, it detects the changes in the magnetic field created by a reluctor ring (a ring with strategically placed interruptions in its magnetic field) attached to the crankshaft pulley. This change in the magnetic field is what tells the Engine Control Unit (ECU) the crankshaft's rotational position and speed, allowing the ECU to precisely time the ignition spark and fuel injection. Therefore, it's not just a simple speed sensor; it's a *positional* sensor critical for the engine's timing.