DTC P0121: Throttle Position Sensor Circuit Range/Performance Problem: DTC Detecting Condition

The ECM compares the actual measured Mass Air Flow signal with the modeled Mass Air Flow value to detect implausible TPS signal. Because throttle position is one of key parameters in determining the modeled MAF.

The DTC P0121 is set when the difference between these two value is too high or too low with lambda deviation in same direction for a certain time.

The ECM illuminates the MIL on the second consecutive driving cycle that the diagnostic runs and fails.

The modeled Mass Air Flow value is determined by engine speed, throttle angle and ISCA duty.