Throttle/Pedal Position Sensor A Circuit Range/Performance
The P0121 code means the vehicle's onboard diagnostic system has detected: Throttle/Pedal Position Sensor A Circuit Range/Performance. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $30-$120
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Common Symptoms
- Check Engine Light on
- Hesitation during acceleration
- Surging idle
- Poor throttle response
- Possible limp mode
Probable Causes (Ranked by Likelihood)
- TPS output does not match expected range at current throttle position Very High
- Worn TPS with dead spots in sweep High
- Throttle plate movement restricted by carbon Moderate
- TPS out of adjustment (older cable-throttle systems) Moderate
Step-by-Step Diagnostic Procedure
-
Use a scan tool to graph TPS voltage while slowly opening the throttle. Look for flat spots or voltage drops that do not correspond to throttle movement.
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Compare TPS reading to throttle blade actual position if second sensor is available.
-
Clean the throttle body and retest.
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If the sensor shows a dead spot, replacement is required.
Common Fixes by Vehicle
What techs usually find when diagnosing P0121 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2020 Ford F-150/Explorer 3.5L/5.0L Easy DIY
TPS signal does not match expected range for current conditions. Usually the throttle body is dirty and the plate is sticking, causing TPS voltage to be out of range at idle. Clean the throttle body with CRC throttle body cleaner. If cleaning does not fix it, the throttle body assembly needs replacement (Motorcraft). Perform idle relearn after any throttle body work.
Labor: 20-30 min2010-2020 Chevrolet Silverado/GMC Sierra 5.3L Easy DIY
TPS range/performance problem. Clean the throttle body -- carbon buildup on the throttle plate prevents full closure and skews TPS readings. If cleaning does not resolve the code, replace the throttle body (ACDelco 12631186). GM requires a throttle position relearn with a scan tool after replacement. Do not open the throttle manually on electronic throttle bodies.
Labor: 20-30 min2008-2019 Honda Accord/CR-V 2.4L Easy DIY
TPS performance out of range. Clean the throttle body thoroughly with throttle body cleaner. On the K24, heavy carbon deposits on the throttle plate cause the TPS to read incorrectly at idle. After cleaning, perform the idle relearn procedure. If the code returns, replace the throttle body assembly (Honda 16400-R40-A02).
Labor: 20 min (clean), 30 min (replace)Frequently Asked Questions
Why does my car hesitate right off idle but then accelerate fine?
This is a classic symptom of a TPS dead spot just off idle (0.5-0.8V range). The ECU briefly loses throttle position data in that range, causing hesitation. Graphing the TPS sweep on a scan tool will reveal the flat spot.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0121 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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