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P0221 means sensor B is moving - just not in lockstep with sensor A. Watch both TPS/APP A and B in live data while you press the pedal slowly: they should mirror each other. If B drifts, lags, or jumps, you've found the fault. See top-rated scanners on Amazon ↑
🗺️ Where Is the Problem?
Blueprint view - P0221 secondary throttle/pedal sensor (B) range/performance vs sensor A
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0221 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
60%
#1 - Most Likely
Worn / Dirty Throttle Body (B sensor side)
Carbon buildup on the throttle plate or wear on the internal B-sensor potentiometer track causes erratic B-sensor output that no longer tracks A. Cleaning sometimes helps; replacement is the permanent fix on most modern drive-by-wire bodies.
🔩 Part
$120–$400
👨🔧 Labor
$80–$160
⚡ DIY Difficulty
Easy
30%
#2 - Check First
Worn Accelerator Pedal Module
On pedals with two redundant Hall-effect sensors, one channel can drift while the other reads correctly. Pedal modules are usually a bolt-in replacement and resolve P0221 cleanly.
🔩 Part
$80–$220
👨🔧 Labor
$60–$120
⚡ DIY Difficulty
Easy
10%
#3 - Less Common
Wiring Resistance / Bad Ground
High resistance in the B-circuit return or ground path skews the signal voltage just enough to fail the range/performance test. Ohm-test the harness pin-to-pin and inspect grounds.
🔩 Part
$10–$60
👨🔧 Labor
$80–$160
⚡ DIY Difficulty
Medium
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Compare TPS/APP A and B in live data - With the engine running (or key-on), slowly sweep the throttle pedal from 0 to 100%. The two sensors should track proportionally. If B lags, jumps, or freezes, that confirms the range/performance fault.
- Clean the throttle body and reset adaptations - Remove the intake duct and clean carbon from the throttle plate with throttle body cleaner. Reset throttle/pedal adaptations with a scan tool and re-test before replacing parts.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need