Circuit Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The Throttle Position (TP) sensors No. 1 and No. 2 are potentiometer type sensors. Both sensor types have a 5-volt reference circuit, a low reference circuit and a signal circuit.
The TP sensor provides the Engine Control Module (ECM) with a signal voltage proportional to the throttle plate movement. The TP sensor 1 signal voltage at closed throttle is about the 5-volt reference and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. When the control module detects that the TP sensors No. 1 and No. 2 signal circuits are out of correlation with each other, DTC P1221 will set.