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 determines operating conditions such as idle (closed throttle), part load, acceleration/deceleration, and wide-open throttle from the TPS. Also The ECM uses the Mass Air Flow Sensor (MAFS) or Manifold Absolute Pressure Sensor (MAPS) signal along with the TPS signal to adjust fuel injection duration and ignition timing.
If the number that throttle angle input signal chages rapidly (above 30%) is 3 times or more, ECM sets DTC P0121.
Item
Detecting Condition
Possible Cause
DTC Strategy
Rationality check
Poor connection
TPS
ECM
Enable Conditions
Counter of signal switching = 3 times
Threshold Value
|? throttle angle| > 30 %
Diagnostic Time
5 sec
MIL ON Condition
3 driving cycle
MAPS
Resistance
Output voltage
1.6 ~ 2.4 ? (20?)
0.2 ~ 4.8 V
1.2 ~ 4.1 V
During acceleration, the TPS output voltage increases; during deceleration, the TPS output voltage decreases. Whenever possible, TPS signal should be compared with the MAPS signal. And check whether the TPS and MAPS signals increase time when accelerating.