Throttle Position Sensor

The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. TP sensor is a potentiometer whose resistance value changes along with the throttle valve position. The Powertrain Control Module (PCM) provides a 5-volt reference voltage to the TP sensor. The PCM reads the voltage across the TP sensor and uses the voltage to calculate the percentage of throttle valve opening. Sensor resistance decreases as the throttle valve opening increases. When the TP sensor resistance decreases the voltage being monitored by the PCM increases. Sensor resistance increases when the throttle valve opening decreases, therefore the voltage being monitored by the PCM will decrease. At a closed throttle position, output of the TP sensor is low. As throttle valve opens, the output increases so that at wide open throttle, output voltage should be more than 3.3 volts.

Because position of the throttle valve controls the air supply to the engine, the PCM can modify the fuel delivery based on throttle angle. For example, power enrichment occurs when throttle angle approaches wide-open throttle. PCM looks primarily for changes in TP sensor output to control fuel delivery. Acceleration enrichment occurs when throttle angle increases, similar to the accelerator pump on a carburetor equipped vehicle.