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)

Or, hide this message: temporarily or permanently

Check Engine Request






If an emission related fault arises in the automatic transmission, the transmission control module sends a PWM signal at a frequency of 2 Hz from pin 5 to engine control module pin 65 (Motronic 4.1).

The engine control module then causes the CHECK ENGINE lamp (MIL) to light up.

When the ignition switch is turned to the ON position, the control module sends a ground pulse for 1 second as an operational check.