Engine Speed (Rpm) Sensor
The engine control module (ECM) uses the signal from the engine speed (rpm) sensor to calculate crankshaft position and speed, enabling it to determine when a piston is approaching its top dead center position (TDC). It cannot, however, use the signal from the engine speed (rpm) sensor to determine if the piston is in combustion position (compression stroke) or if the exhaust valve is open (exhaust stroke). The camshaft position sensor signal is also needed to determine the operating cycle of the engine. When the reference hatch on the crankshaft flywheel passes the engine speed (rpm) sensor, voltage and frequency instantly drop to zero.
This enables the engine control module (ECM) to determine the position of the crankshaft.
There is a steel ring with stamped holes welded to the rim of the primary section (the section fixed to the crankshaft) of the flywheel.
The holes are positioned with a gap of 6° between each hole. This arrangement creates a hole for each tooth. There are 360° in one revolution. 6° between each hole means that there are 60 holes. However, two holes are not stamped, to create a reference position (long gap - missing tooth) for the crankshaft. The first tooth after the reference position is located 84° before TDC on cylinder 1.
Engine control module (ECM) also uses the signal from the engine speed sensor to calculate the engine's rpm by counting the number of holes per time unit and the direction of the vehicle.
The impulse sensor uses the Hall principle. On the fly wheel there is a magnetic disk positioned with north and south poles. When the flywheel rotates an alternation of the south and north poles towards the sensor is created, which results in a sine wave. In the impulse sensor the sine curve is converted to a PWM signal, which provides the engine control unit (ECM) with information about engine speed.
The engine speed sensor is located at the flywheel (at cylinder 5).
The engine speed sensor can be diagnosed by the engine control module (ECM) and the sensor signal (engine speed) can be read out.