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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Knock Sensor: Testing and Inspection

1. Disconnect knock sensor connector and remove knock sensor from vehicle. Mount knock sensor in the jaws of a bench vise and connect a voltmeter between terminals 1 and 2.
2. Wrap on the bench vise sharply with a hammer an observe voltmeter.
3. Verify that a voltage spike (less than 1 V) is output from the knock sensor.
4. If no voltage spike is observed, replace the knock sensor.