What is the meaning of OBD-II code P0121, and what are the possible causes and solutions for this code to be generated?

P0121 is a standard OBD-II diagnostic code that signals the Engine Control Module (ECM) has detected an irregularity in the voltage output of the Throttle Position Sensor (TPS) circuit A. This irregularity is detected when the voltage is either higher or lower than what is expected when compared to TPS sensor circuit B. There are several possible causes for a P0121 code, such as: -TPS sensor circuit A output to ECM exceeds specified voltage difference with TPS sensor circuit B by more than 1.6 volts -TPS sensor circuit A output to ECM is less than the specified voltage difference with TPS sensor circuit B by going less than .8 volts. To diagnose the problem, a mechanic will typically scan codes, clear faults, check TPS connections and wiring, and compare TPS circuit data, with pinpoint tests if necessary. The resolution for the P0121 code will depend on the cause, but potential fixes include repairing/replacing the TPS connector, repairing wiring, and replacing the TPS with a new sensor. The P0121 code may indicate a faulty TPS sensor, and other TPS codes may accompany it requiring additional repairs. All TPS codes result in the ECM entering failsafe mode and have similar driving symptoms.