Manuals through 2025 now available!
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LEMON is the spiritual successor to CHARM, I recommend you try it!
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Vehicle Speed Sensor: Description and Operation
The
Vehicle Speed Sensor is an integral part of the speedometer assembly. The ECM applies and monitors a 12V signal to the sensor. When the drive wheels are turning, the sensor alternately grounds the circuit, creating a pulsing action. The ECM calculates vehicle speed based on the time between pulses.