DTC P0121: Throttle Position Sensor Circuit - Range/Performance Problem: Condition
WARNING: This page is about a different car, the 2002 Suzuki XL-7. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0121 is set when throttle opening value is less than predetermined while intake air volume changes and engine is running at a constant speed. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles.