Reluctor ring?

[mfw898y]

Off the top of my head it consists of a toothed ring and a sensor in close proximity. The sensor has coiled wire in it with a voltage applied creating a magnetic field. When a ferrous metal passes through this field, it changes the voltage and/or resistance (somethin to do with magnetic flux) which is sensed up by ECU. This is how it knows when to spark the plugs or unlock the brakes when ABS senses wheels locked.

I refer to them as a phonic wheel and sensor at work, vx call it a reluctor ring as this thread suggests and they called it hall effect to do with ignition timing.:confused:

[trev150]

The Hall effect to a DC system is the same thing as inductance to an AC system.