P2121

P2121 is the range/performance variant of P2120 — the 'D' channel pedal-position sensor is reading within electrical limits (not open, not shorted) but its value doesn't make physical sense relative to either the APP-E sensor or the driver's actual pedal input. Example: APP-D reads 2.5V (mid-travel) while APP-E reads 0.5V (rest) — both are electrically valid but they can't both be true simultaneously, so the ECM throws P2121. This is the early-warning code for a worn pedal sensor where the wiper element is starting to flat-spot but hasn't fully failed yet. Cheapest-first: same as P2120 — unplug the pedal connector, inspect for corrosion, backprobe APP-D and APP-E simultaneously, and watch them on a scope as you slowly sweep the pedal. A healthy pair sweeps in clean mirror image with no flat spots, no dropouts, and no hysteresis. A failing sensor shows a brief flat spot at one specific pedal position (usually around the wear zone from years of daily driving — about 15-20% open), and that flat spot is where P2121 triggers. If APP-E is clean and APP-D has the flat spot, the pedal assembly needs replacement (the sensor isn't serviceable separately on most platforms).

Vehicle-specific patterns: 2008-2014 Honda Accord / Pilot / Odyssey / Ridgeline with the J35 / K24 is a high-incidence P2121 platform — the pedal sensor wears at the rest position from highway commuting (foot held at the same partial-throttle angle for hours daily) and develops a flat spot that throws P2121 with P2127 as a companion. 2007-2012 Nissan Altima / Maxima sees P2121 from the same pedal-sensor wear pattern. 2006-2010 BMW E90 (328i / 335i) throws P2121 from connector corrosion at the pedal-to-firewall transition where road salt wicks up through the floor-pan gap. 2010-2015 Hyundai Sonata / Tucson gets P2121 from a known internal pedal-sensor fault under warranty extension on certain VIN ranges. Critical: never replace the throttle body for P2121 — this is a pedal-side code on every modern ETC platform. The throttle body has its own TPS-A and TPS-B sensors (which throw P0120-series codes when they fail), and they're electrically independent from the pedal sensors.