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I'm replacing a front wheel speed sensor unit on an '04 YS3F saloon, it's the metal ring type that clips onto the rear of the hub assembly. Sitting underneath the old unit when I removed it was something resembling a flat carbonized rubber ring, would this be a reluctor ring? There was nothing in the packaging with the new replacement sensor unit, but I'm wondering a) what is it? and b) should it be replaced? Thanks guys
 

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I'm replacing a front wheel speed sensor unit on an '04 YS3F saloon, it's the metal ring type that clips onto the rear of the hub assembly. Sitting underneath the old unit when I removed it was something resembling a flat carbonized rubber ring, would this be a reluctor ring? There was nothing in the packaging with the new replacement sensor unit, but I'm wondering a) what is it? and b) should it be replaced? Thanks guys
The wheel speed sensor detects the rotatiional speed of the wheel. It determines this speed via the sensor, the sensor is physically mounted nearby a portion of the wheel that rotates and has "gear teeth", "ridges" on a circular rotating portion of the wheel. A simple check of the operation of the sensor can be done by disconnecting the sensor wire connector at the wheel. Use a DVM meter in Ohms position and read the resistance directly at the Speed Sensor connector, this test applies only or a 2 wire reluctance type sensor. Also, you can switch the two front or two rear sensors , to determine if the Error code moves to that side of the car and confirm if the error code is now on the other side of vehicle. Sometimes the Rotating Ring or Riged Hub that the sensor is monitoring is dirty and does not allow the sensor to accurately detect the rotation because it can't read consistently the moving "gear teeth or ridge rings" due to dirt clogged up on these components. Last resort is to jack up vehicle SAFELY, put the transmission in drive and monitor the output signal of the Sensor with an Oscilloscope.
 
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