What Does P0121 Mean on a 2021 Hyundai Sonata?
P0121 on your 2021 Hyundai Sonata tells our diagnostic team that the throttle position sensor (TPS) is transmitting voltage within the expected range but with an abnormal signal pattern. The ECM detects a mismatch between TPS data and its calculations from pedal input, airflow, and engine load.
The 2021 Sonata is part of the eighth generation (DN8), available with the 2.5L MPI (191 hp), 1.6L Turbo GDI (180 hp), or 2.5L Turbo GDI (290 hp in the N-Line). The MPI engine's port injection keeps the throttle body clean, while the GDI engines are more carbon-prone. All pair with an 8-speed automatic or DCT.
Common Symptoms to Watch For
- Check engine light on
- Hesitation during acceleration
- Rough or hunting idle
- Transmission shifts feel off
- Reduced throttle response
- Fuel economy slightly decreased
Top Causes Ranked by Likelihood
- Carbon buildup on throttle body (30%) – At 3-5 years, early deposits are possible, especially on GDI engines. Cost: $120–$275.
- Throttle body assembly failure (25%) – Internal TPS defect. Cost: $0 under warranty; $250–$480 otherwise.
- ECM software calibration (25%) – An available update. Cost: $0 under warranty.
- Wiring or connector issue (15%) – Corrosion or assembly variability. Cost: $0 under warranty; $80–$220 otherwise.
- Intake system leak (5%) – A gasket or boot issue. Cost: $0 under warranty; $75–$250 otherwise.
How Serious Is This Code?
P0121 is medium severity. Fix this soon—Hyundai's warranty makes it painless.
Diagnostic Path
Your 2021 Sonata is well within warranty. Let the dealer diagnose with GDS—it's free.
Can You Fix This Yourself?
Hyundai's 5yr/60k basic warranty covers your 2021 Sonata. Original owners have the 10yr/100k powertrain warranty. Dealer repair is free.
Get a Free AI Diagnosis
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