Operation CHARM: Car repair manuals for everyone.
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

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Vehicle Speed Sensor: Description and Operation


The vehicle speed sensor is mounted in the instrument cluster and provides a pulsating voltage signal from which the ECM determines vehicle speed. As vehicle speed increases, the frequency of the VSS voltage pulsations increases, allowing the ECM to determine optimum EGR and preventing TCC engagement at low speeds.