Prizm L4-108 1.8L DOHC VIN 8 MFI (1995)
Throttle Position Sensor: Description and Operation
DESCRIPTION
The Throttle Position (TP) sensor is a "three-wire" sensor or potentiometer with a five-volt reference input from the PCM to the sensor, a
reference ground from the PCM and a sensor output signal from the sensor to the PCM.
OPERATION
The sensor output signal is an AC voltage that varies with throttle angle. As the throttle angle is changed (accelerator pedal moved), the output of
the TP sensor also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle opens, the output increases so that, at
wide-open throttle, the output approaches five volts.
FUEL DELIVERY CALCULATIONS
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 TP sensor output to control fuel delivery.
Acceleration enrichment occurs when the throttle angle increases, similar to an accelerator pump on a carbureted vehicle.
IDLE SWITCH
The TP sensor also houses an idle switch. The PCM supplies both resisted ignition voltage and a ground to the idle switch. When the throttle is
closed, the PCM senses the voltage drop caused by the switch closed to ground. The PCM uses this information as a reference for idle air control
information.
TP SENSOR CIRCUIT FAILURE
A failure in the TP sensor circuit should set a Diagnostic Trouble Code (DTC) 41 Throttle Position Sensor Circuit.
