A ferromagnetic ring with evenly spaced teeth or notches, mounted on a rotating component like a crankshaft, camshaft, or wheel hub. As it spins, the teeth pass by a stationary variable reluctance sensor or Hall effect sensor, disrupting its magnetic field. This generates a pulsed voltage signal that the engine computer uses to determine RPM, ignition timing, or wheel speed for ABS.
The ABS light is on because the reluctor ring on the right front axle rusted out and snapped.
A cracked reluctor ring will often cause false ABS activation at low speeds before it completely fails and sets a code.
Also heard as
- reluctor ring
- tone ring
- trigger wheel
Related terms
ABS
The anti-lock braking system prevents wheels from locking up during emergency stops.
ECU
The primary computer that manages engine performance, fuel delivery and emissions.
Ignition timing
The exact moment a spark plug fires relative to the position of the piston during the compression stroke.
Computer-controlled timing
An ignition system where an electronic control unit determines exactly when to fire the spark plugs.