Circuit Description

Throttle Position (TP) sensor is a potentiometer whose resistance changes along with throttle valve position. PCM provides a 5-volt reference voltage to TP sensor. PCM reads voltage across sensor and converts it into a reference for throttle position. When TP sensor resistance decreases, throttle valve opening is increasing to Wide Open Throttle (WOT) and voltage being monitored at PCM increases. When TP sensor resistance increases, throttle valve opening is decreasing to idle and voltage being monitored at PCM decreases.

DTC P0121 will set when difference between expected TP sensor and actual input is greater than 11° for at least 3 seconds. Conditions for DTC to set are:

• Engine speed is 1500-3000 RPM.
• Coolant temperature is greater than 158°F (70°C).
• Intake air temperature is 14-122°F (-10-50°C).
• Fuel level is greater than 25 percent.
• Barometric pressure is greater than 11 psi (75 kPa).
• MAP change is less than.14 psi (13 kPa) per 16 firing events.