P1121 on a BMW means the engine control module (DME) has detected that the signal from pedal position sensor 1 is outside the expected range or is not correlating correctly with the other pedal sensor or with the throttle valve position. The DME compares the two redundant pedal sensors and expects them to track together within a tight tolerance, so this code sets when sensor 1's voltage or rationality check fails during the self-test or while the pedal is being pressed.
Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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