Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

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Vehicle Speed Sensor: Description and Operation

Vehicle Speed Sensor:

Vehicle Speed Sensor is an integral part of speedometer assembly. ECM applies and monitors a 12V signal to sensor. When drive wheels are turning, sensor alternately grounds circuit, creating a pulsing action that occurs 4096 times per mile. ECM calculates vehicle speed based on time between pulses. This input is used by ECM for idle air and fuel control calculations.