Possible causes

– Faulty throttle position sensor
– Throttle position sensor harness is open or shorted
– Throttle position sensor circuit poor electrical connection
– Faulty Powertrain Control Module (PCM)

When is the code detected?

Sensor input voltage does not fall within a valid range based on engine speed and load

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0121 2003 JEEP LIBERTY Description

The Throttle Position Sensor (TPS) responds to the accelerator pedal movement. This sensor is a kind of potentiometer which transforms the throttle position into output voltage, and emits the voltage signal to the Powertrain Control Module (PCM). In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the PCM.
Idle position of the throttle valve is determined by the PCM receiving the signal from the throttle position sensor. This sensor controls engine operation such as fuel cut. On the other hand, the Wide open and closed throttle position switch, which is built into the throttle position sensor unit, is not used for engine control.

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