The older electronic speed sensors on EEK cars were functionally the same... until they went to the Hall-Effect units in the early 90's (about 1992 to 1993). For the older units, you basically had a sealed unit with a micro switch that produced 8 pulses per revolution... i.e contact closures.
Depending on the car (you didn't give us the year), the computer used the speed sensor to determine when a moving car has come to a stop. The computer then adjusted the AIS motor to set the idle speed. A malfunctioning speed sensor could create a stall or stumble at that point, and usually a code 15 was stored.
The most common cause of the code 15 was a bad connection at the speed sensor plug. Later there were improved connectors to help improve that situation. Occasionally you could get an internal problem in a speed sensor and have a hard failure. Assuming you had an electronic speedometer, it would fail to register along with the odometer.
Some of the earlier speed sensors were a hybrid type that had the mechanical drive for the speedometer/odometer but also had the pulse contacts for the computer to use and for cruise control module.
Regarding the pinion gear, the different # of teeth on the different color gears was for speedometer/odometer calibration for different size tires or differential gear differeneces.
Depending on the car (you didn't give us the year), the computer used the speed sensor to determine when a moving car has come to a stop. The computer then adjusted the AIS motor to set the idle speed. A malfunctioning speed sensor could create a stall or stumble at that point, and usually a code 15 was stored.
The most common cause of the code 15 was a bad connection at the speed sensor plug. Later there were improved connectors to help improve that situation. Occasionally you could get an internal problem in a speed sensor and have a hard failure. Assuming you had an electronic speedometer, it would fail to register along with the odometer.
Some of the earlier speed sensors were a hybrid type that had the mechanical drive for the speedometer/odometer but also had the pulse contacts for the computer to use and for cruise control module.
Regarding the pinion gear, the different # of teeth on the different color gears was for speedometer/odometer calibration for different size tires or differential gear differeneces.