What Does P0121 Mean on a 2021 Ford Bronco Sport?
A P0121 code on your 2021 Ford Bronco Sport tells our diagnostic investigators that the throttle position sensor (TPS) is sending signals within the normal voltage range but with an abnormal performance pattern. The PCM detects that the TPS readings don't align with expected values based on engine load, MAF data, and other sensor inputs.
Your Bronco Sport rides on Ford's C2 platform and comes with either a 1.5L EcoBoost three-cylinder (181 hp) or the 2.0L EcoBoost four-cylinder (250 hp) in Badlands trim. Both engines use electronic throttle control with an integrated TPS built into the throttle body assembly. The direct-injection design on both engines makes them susceptible to carbon buildup that can affect throttle body operation.
Common Symptoms to Watch For
- Check engine light or wrench light on the dash
- Hesitation when accelerating from a stop
- Rough or hunting idle
- Reduced power, especially noticeable on inclines or during towing
- Jerky throttle response at low speeds
- G.O.A.T. mode selection may behave erratically if throttle input is inconsistent
Top Causes Ranked by Likelihood
- Carbon buildup on throttle body (40%) – Direct injection means no fuel washing across intake valves or the throttle bore. Carbon accumulates on the throttle plate and housing, restricting smooth movement and creating abnormal TPS voltage patterns. Cost: $150–$300 for professional cleaning.
- Throttle body assembly failure (25%) – The integrated TPS can develop internal wear on the resistive element, creating dead spots or erratic signals during throttle sweeps. Cost: $350–$550 for replacement including relearn.
- Connector or wiring harness damage (20%) – The Bronco Sport is designed for light off-road use, and trail debris, water intrusion, or vibration can compromise the throttle body connector or wiring. Cost: $100–$250 for repair.
- PCM calibration issue (10%) – First-year models sometimes have software refinements issued via TSBs. An outdated PCM calibration can trigger P0121 under specific conditions. Cost: $100–$180 for dealer reflash.
- Intake system air leak (5%) – A loose clamp or cracked intake boot between the turbo and throttle body can cause airflow discrepancies that conflict with TPS data. Cost: $50–$200.
How Serious Is This Code?
P0121 is a medium severity code. Your Bronco Sport will likely still drive, but may exhibit reduced power or erratic throttle response. This is especially concerning during off-road driving where precise throttle modulation matters. Plan to have it inspected soon—within the next week.
Diagnostic Path
Start the investigation by connecting FORScan to read live TPS voltage data. Monitor the signal during a slow, smooth throttle sweep from closed to wide-open. Look for any voltage dropouts, dead spots, or sudden jumps—these are the key clues. At closed throttle, expect 0.5–0.9V; at wide-open throttle, 4.0–4.5V.
Visually inspect the throttle body for carbon deposits. On the 1.5L three-cylinder, access is straightforward from the top of the engine. Check the connector for water intrusion—a common finding on vehicles used in wet conditions. Review Ford's TSB database for any software updates applicable to your build date.
Can You Fix This Yourself?
As a 2021 model, your Bronco Sport's 3yr/36k basic warranty may still apply depending on mileage—check your coverage first. Throttle body cleaning is a moderate DIY task. Throttle body replacement is feasible for experienced DIYers, but the relearn procedure requires FORScan or a dealer visit.
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