What a reluctor sensor is
A variable reluctance sensor, usually called a VR sensor or just a reluctor, is a small magnet wrapped in a coil of wire. It sits close to a toothed wheel made of steel or another ferrous metal. Each time a tooth sweeps past, it disturbs the magnet's field, and that change induces a voltage in the coil. The result is an AC signal that swings positive and negative, roughly a sine wave, once per tooth.
It's the same principle as a generator in reverse: nothing is powered, the motion of the wheel creates the signal. That's why these sensors are so durable and so common on crank and cam triggers.
How to recognize one
| Reluctor (VR) | Hall effect / optical | |
|---|---|---|
| Wires | Usually 2; a third is typically a shield | Usually 3: power, ground, signal |
| Needs power? | No | Yes |
| Output | AC wave, gets bigger with speed | Clean on/off square wave |
| Main weakness | Weak signal at cranking speed, sensitive to noise | Needs a supply; electronics can fail from heat |
A third wire on a reluctor is normally a shield that protects the signal from electrical noise, not a power feed. Connect it as a shield, not to 5V or 12V. Our Hall effect and optical sensors page covers the other family, and Hall effect or reluctor? helps you work out which you have.
What the ECU does with the signal
An ECU can't time spark and injection from a raw sine wave. It needs a clean edge it can measure. Inside the Elite, a reluctor adapter conditions the incoming AC signal and turns it into a square wave, similar to what a Hall sensor would produce. From there, the ECU treats it like any other digital trigger.
Because the signal is small at low RPM and grows with speed, the adapter's settings matter. If it's too sensitive, noise gets through as false teeth. If it isn't sensitive enough, the ECU misses teeth while cranking. See trigger arming voltage for how to tune that threshold.
Wiring tips
- Use shielded cable and ground the shield at one end only.
- Polarity matters. If the ECU sees the wave upside down, it will time off the wrong edge and timing will wander. Swapping the two wires is the usual fix.
- Keep it away from coils and plug leads. Reluctor signals are low level and easy to corrupt.
- Check the air gap. Too big a gap means a weak signal, especially when cranking.
Full wiring details are in trigger wiring for crank and cam sensors.
