Engine Light ON (or Service Engine Soon Warning Light)
P1221 Chevrolet Description
The Throttle Position (TP) Sensor is mounted on the throttle body of the Throttle Actuator Control (TAC) assembly. The sensor is actually 2 individual throttle position sensors within 1 housing. Two separate signal circuits, a low reference circuit, and a 5-volt reference circuit are used in order to connect the TP sensor assembly and the TAC module. The TP sensor signal voltage increases as the throttle opens. The signal circuit for TP sensor is pulled up to 5-volt reference voltage.