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Variable Reluctance Sensor (VRS)

The VRS is used on 4.0L Explorer and Ranger. The VRS transmits crankshaft position and RPM information. It is a passive electromagnetic device, which senses movement of a 35-tooth wheel (wheel has a gap at 60 degrees BTDC, where the 36th tooth would have been, for triggering). The VRS is located behind crankshaft pulley.

An AC voltage signal, generated by VRS, increases with engine RPM and provides basic spark timing information to ignition module. Ignition module uses this input to produce a PIP signal to PCM. The PCM responds with a Spark Angle Word (SAW) signal, which, along with VRS signal, is used by ignition module to compute basic spark timing and determine which coil pack to trigger.

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