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 logical successor to CHARM, I recommend you try it!

Link: lemon-manuals.la

Component Testing

The engine knock sensor is affected by a number of factors. A few of these are:
- ignition timing
- cylinder pressure
- fuel octane, etc.

The knock sensor generates an AC voltage whose amplitude increases with the increase of engine knock.

The knock sensor can be tested with a digital voltmeter:
- The RMS voltage starts at about 20mVac (at about 700 rpm) and increases to approximately 600 Vac (5,000 rpm).
- If the output falls outside of this range a DTC will be set.