Possible causes

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

When is the code detected?

Malfunction is detected when an excessively low or high voltage from the sensor is sent to ECM.

Symptoms

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

P0121 CADILLAC 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 Engine Control Module (ECM). In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM.
Idle position of the throttle valve is determined by the ECM 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.

CADILLAC Technical Service Bulletins for P0121 code