DTC P0121: TP Sensor No. 1 Circuit Performance: Description

Throttle control module contains 2 Throttle Position (TP) sensors with a common 5-volt supply, a common ground and 2 independent signal circuits that vary resistance according to changes in throttle plate position. ECM measures signal voltage from each TP sensor, which is a reduced value of ECM 5-volt reference. As the throttle plate opens from zero percent throttle to wide open throttle, voltage on TP sensor No. 1 signal increases from 0.4-0.6 volt to 4.1-4.4 volts, while voltage on TP sensor No. 2 signal decreases from 4.3-4.6 volts to 0.6-0.8 volt. DTC sets when TP sensor No. 1 and TP sensor No. 2 are out of correlation, and TP sensor No. 1 indicates too large a difference in throttle angle based on MAF reading.