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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Ignition Diagnostic Monitor (IDM)

PURPOSE
The Ignition Diagnostic Monitor (IDM) is a function of the Powertrain Control Module (PCM). Information on system failures is stored within the PCM and used for diagnostic self-tests.

OPERATION
The IDM signal is transmitted on each spark firing. This signal communicates information by pulse width modulation and provides a clean buffered signal with a frequency proportional to engine speed for tachometer operation.