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

(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

A Vehicle Speed Signal is sent to the Motronic control module from the Vehicle Speed Sensor located in the transmission, the signal is directional IN only (PIN 65 - INPUT ONLY).

The vehicle speed signal is information about the current vehicle speed and is supplied to the Motronic control module via the speedometer.

The signal is used for idle air control (active below 4 mph) and A/C compressor cut-out.

Self-diagnosis:

^ Self-diagnosis (OBD) recognizes the fault "no signal".