The Throttle Position Sensor (TPS) is mounted on the throttle body and detects the opening angle of the throttle plate. The TPS has a variable resistor (potentiometer) whose characteristic is the resistance changing according to the throttle angle. During acceleration, the TPS resistance between the reference 5V and the signal terminal decreases and output voltage increases; during deceleration, the TPS resistance increases and TPS output voltage decreases. The ECM supplies a reference 5V to the TPS and the output voltage increases directly with the opening of the throttle valve. The TPS output voltage will vary from 0.2~0.8V at closed throttle to 4.3~4.8V at wide-open throttle
The ECM compares the actual measured Mass Air Flow signal with the modeled Mass Air Flow value to detect implausibile 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 dirrection 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.
Item
Detecting Condition
Possible cause
DTC Strategy
? Rationality check
? Poor connections
? Faulty TPS
? Faulty ECM
? Open or short in battery circuit
? Dirty air cleaner
? Air leak in intake system
? Contaminated, deterriorated or damaged TPS
General Enable Condition
? Off idle
? Deviation of fast lambda control factor from 1.0 < 0.1
? Engine coolant temperature > 85 degC
? Engine speed > 600 rpm
? Gradient of TPS signal < 0.12 %
Threshold value
case1
? Difference between load signal by Map sensor and load signal calculated by TPS < 0.75
? Difference between load signal by Map sensor and load signal calculated by TPS > 1.25
case2
? Modeled relative load ? relative load > threshold f(TPS)
case3
? Modeled relative load ? relative load > threshold f(relative load)
case4
-
Enable Conditions
? Engine speed > target idle speed
? 20sec after engine start
? Vehicle speed = 0 kph
? Vehicle speed > 0 kph
Diagnostic Time
? 25 sec
?
TPS
Normal Parameter
Idle position
WOT
Throttle angle
0 ~ 0.5°
90 ~ 100°
Signal Voltage
0.2 ~ 0.8 V
4.2 ~ 4.8 V
Resistance(terminal 1 and 2)
0.71 ~ 1.38 ?
2.2 ~ 3.4 ?
Resistance(terminal 2 and 3)
1.6 ~ 2.4 ? at all throttle position
Hi-scan Data display
0%
75 ~ 85 %
When checking TPS waveform,it is strongly recommended to examine waveform with MAP sensor waveform.
Periode ? Is the voltage of MAP in idling and 0.8~1.2 V,and there must be a little fluctuation in waveform.
In case there is no fluctuation
Possible cause : Deteriorated MAP sensor or some foreign material in TPS sensor.
The voltage in Periode ? Is 0.3~1.0V in average.
Periode ? Is in W.O.T and the voltage there is 4.3 V, and MAP sensor voltage is about 4.3 V.