Scoupe L4-1468cc 1.5L SOHC (8 VALVE) (1991)
/Page-415001.png)
Top Dead Center (TDC) Sensor: Description and Operation
Crank Angle And #1 TDC Sensor Location
Crank Angle And #1 TDC Sensor
The crankshaft angle sensor and the No.1 cylinder TDC sensor are composed of a disc and unit assembly. The disc is a metal disc which has four
light-transmission slits located 90° apart around its circumference. There is also one additional slit located inward from these four. The inner slit is for
the No.1 cylinder TDC sensor, and the outer slits are for the crankshaft angle sensor.
The disc is affixed to the distributor shaft. When the shaft rotates, the slits in the disc are optically read by the unit assembly. The unit assembly, in order
to be able to detect the two types of slits, incorporates two luminous diodes and two photo diodes. There is a very slight clearance between the luminous
diodes and the photo diodes, and the disc rotates within this space.
Crank Angle And #1 TDC Sensor System
The light emitted from the luminous diodes reaches the photo diodes each time the disc turns. When the photo diodes receive the light transmitted, they
become conductive in the direction opposite to that of ordinary diodes, with the result that current flows as shown by the arrows in the crank angle and
#1 TDC sensor system images, and approximately 5v is applied to the comparator. When this happens, 5v is transmitted from terminal 2 to the ECU.
Because the light to the photo diodes is interrupted when the slit passes, the current shown by the broken line stops flowing, and terminal 2 becomes O
volts. In this way, then, the pulses from the unit assembly are sent to the ECU as signals.
