Prizm L4-108 1.8L DOHC VIN 8 MFI (1998)
Throttle Position Sensor: Description and Operation
Throttle Position (TP) Sensor
The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the
PCM calculates throttle position. As the throttle valve angle changes (accelerator pedal moved), the TP sensor signal also changes. At a closed throttle
position, the output of the TP sensor is low. As the throttle valve opens, the output increases so that at wide open throttle, the output voltage should be
above 3.3 volts. By monitoring the output voltage from the TP sensor, the PCM can modify fuel delivery based on throttle angle. For example, power
enrichment occurs when the throttle angle approaches wide.open throttle. The PCM looks primarily for changes in the TP sensor output to control fuel
delivery. Acceleration enrichment occurs when the throttle angle increases, similar to an accelerator pump on a carbureted vehicle.