What is a VW Jetta engine speed sensor?
The engine speed sensor provides the ECM with a crankshaft
position signal. The ECM uses the signal to determine a crankshaft
reference point (Top Dead Center) and calculate engine speed (RPM.)
The signal is also used by the On-Board Diagnostic system for
misfire detection. The ignition system will not operate if the ECM
does not receive an engine speed sensor input.