P0221

P0221 means TPS sensor B is reporting a voltage that is in-range electrically but does not correlate with engine load, MAF airflow, or the TPS-A signal — a rationality fault rather than an open/short. The cheapest diagnostic is a slow-sweep test: with the engine off and ignition on, slowly open the throttle by hand (or by accelerator pedal on drive-by-wire) while watching both TPS-A and TPS-B on a graphing tool — any flat spot, glitch, or non-mirrored region in TPS-B's sweep is the defect. TPS-A should climb smoothly from ~0.5 V to ~4.5 V; TPS-B should descend (or ascend on some platforms) just as smoothly with no dropouts. Check the 5 V reference for sag under load and confirm sensor ground integrity (under 100 mV drop). Caveat: carbon buildup on the throttle plate can cause the plate to hang at a slightly different mechanical position than the PCM expects from learned closed-throttle, which trips P0221 without any actual sensor fault — always do an induction clean and throttle relearn before condemning the throttle body.

Vehicle-specific patterns: 2008-2013 GM 5.3L truck (LMG/LC9) with AFM — carbon coking around the throttle plate edge causes intermittent P0221; throttle-body service and idle/ETC relearn via Tech 2 or equivalent resolves most cases. 2006-2011 Toyota Tacoma 4.0L (1GR-FE) — the integrated TPS develops a dead spot around 15-20% opening; ETB replacement (22030-31010) is the documented fix. 2007-2012 Nissan Altima 2.5L (QR25DE) — electronic throttle control actuator failure under TSB NTB10-082, ETB part 16119-JA00A. 2005-2010 Ford Mustang 4.6L 3V — TPS-B nonlinearity from connector pin fretting; clean and apply dielectric grease before replacing the throttle body. Estimated repair: $90 to $550.