Throttle Position Sensor: Testing and Inspection

A "Scan tool" displays throttle position in volts. Throttle position (TP) sensor voltage should read below 0.85 volts, with throttle closed and ignition "ON", or at idle. Voltage should increase at a steady rate as throttle is moved toward wide open throttle. The Engine Control Module (ECM) has the ability to auto-zero the TP sensor voltage if it is below about 0.85 volts. This means that any voltage less than 0.85 volts will be determined by the ECM to be 0% throttle.

Some "Scan tools" have the ability to read the throttle angle and should read 0%, when the throttle is closed. A failure in the TP sensor or circuit should set a DTC 21.