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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Engine Speed (RPM) Signal, Checking




Engine Speed (RPM) Signal, Checking


NOTE: The engine speed signal is taken from terminal 37 on the Engine Control Module (ECM). The signal is used for various functions including the RPM display in the instrument cluster.







- Connect VAG1598/31 test box to wiring harness for engine control module. Do not connect to the engine control module itself. Refer to "Scan Tool Testing/Wiring And Component Check With VAG1598/31 Test Box", Testing and Inspection
- Check wiring from test box socket 37 to instrument cluster according to wiring diagram for an open circuit.