P0121 on a 2017 Honda Civic
Throttle Position Sensor Range / Performance
P0121 on a 2017 Honda Civic indicates throttle position sensor range / performance. It usually stays drivable short-term but should be diagnosed promptly. The most common cause is worn throttle position sensor (mechanical tps wear) (typically $100–$400). Confirm the root cause before replacing parts.
What does P0121 mean on a 2017 Honda Civic?
P0121 is set when the engine control module sees the throttle position sensor signal moving outside its expected range or changing in a way that does not match other inputs (MAP, MAF, engine load). The TPS reports where the throttle blade is — inputs like accelerator pedal position, engine load, and idle control all depend on accurate TPS readings. Bad TPS data triggers reduced-power or limp mode on many vehicles.
This guide covers P0121 across the 2015-2019 Honda Civic generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2015 through 2019.
Is it safe to drive a 2017 Honda Civic with P0121?
In most cases a 2017 Honda Civic stays drivable for short trips with P0121 active, but diagnose and repair it promptly. This is a high-severity code — ignoring it can lead to further damage or a failed emissions test.
What are the symptoms of P0121 on a 2017 Honda Civic?
- Check Engine Light is illuminated
- Throttle hesitation or surging at light pedal input
- Stalling when coming to a stop
- Reduced engine power / limp mode
- Erratic or hunting idle
- Slow or absent throttle response
- On electronic-throttle vehicles, may set ETC fault / wrench icon
What causes P0121 on a 2017 Honda Civic?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Worn throttle position sensor (mechanical TPS wear) | Most common | $100–$400 |
| Carbon buildup in the throttle body causing the blade to bind | Common | $20–$200 |
| Corroded TPS connector or damaged signal wiring | Common | $50–$250 |
| Failed electronic throttle body (combined ETB / TPS unit) | Common | $250–$800 |
| TPS sensor needs reset / relearn after battery disconnect | Occasional | $0–$100 |
| Damaged accelerator pedal position sensor (separate code in some cases) | Occasional | $200–$600 |
| PCM input fault (rare) | Rare | $400–$1,500 |
How to diagnose this on a 2017 Honda Civic
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Identify whether this is a cable or electronic throttle
Older vehicles use a cable from the gas pedal to the throttle body, with a TPS sensor that reports actual blade position. Modern vehicles use electronic throttle control (ETC) — pedal position is one sensor, throttle blade position is another, and the ECM controls the motor. The diagnostic differs.
Tools: Vehicle-specific service information
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Watch TPS voltage sweep with the scan tool
With the key on and engine off, slowly press the throttle from closed to wide open while watching the TPS voltage PID. A healthy sweep is smooth and linear, typically 0.5 V at closed throttle and 4.5 V at wide-open. Glitches, dropouts, or a jumpy reading confirm a worn sensor.
Tools: Scan tool with TPS PID
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Clean the throttle body
Carbon buildup inside the throttle body causes the blade to stick or close incompletely, which gives bad TPS readings even with a perfect sensor. Use throttle body cleaner (NOT carb cleaner — too aggressive on electronic throttle coatings) and a soft brush. On electronic throttle, perform a relearn after.
Tools: Throttle body cleaner, Soft-bristle brush, Shop towels
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Perform a throttle position relearn
Battery disconnection, ECM reset, or throttle body cleaning requires a relearn procedure on most modern vehicles. The procedure varies — typically key on, wait 30 seconds, start the engine, idle 5 minutes. Some vehicles need a bidirectional scan tool to perform an idle relearn.
Tools: Service manual procedure, Bidirectional scan tool (some vehicles)
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Inspect the connector and signal wiring
Unplug the TPS / ETB connector and inspect for water intrusion, corrosion, or bent pins. Engine-bay-mounted connectors fail with age. Apply dielectric grease on reinstall.
Tools: Electrical contact cleaner, Dielectric grease
Known Technical Service Bulletins for the 2015-2019 Honda Civic
Manufacturers publish Technical Service Bulletins (TSBs) when a known issue affects a specific vehicle. These bulletins come from the NHTSA database for your Honda Civic.
- ENGINE Jul 28, 2025
Service Bulletin - Oil leak at timing chain tensioner inspection cover due to possible insufficient sealant adhesion on inspection cover.
NHTSA #11021745 - FUEL/PROPULSION SYSTEM Aug 6, 2024
Dealer Message - American Honda Motor Co., Inc. (AHM) is searching for certain 2018-2020 Accords, 2016-2020 Civics, 2017-2020 CR-Vs, & 2018-2020 Odysseys that have been diagnosed to be in need of the low-pressure fuel pump, fuel strainer, fuel meter or fuel tank replacement.
NHTSA #11006249 - FUEL/PROPULSION SYSTEM Jul 22, 2024
Dealer Message - American Honda Motor Co., Inc. (AHM) is searching for certain 2018-2020 Accords, 2016-2020 Civics, 2017-2020 CR-Vs, & 2018-2020 Odysseys that have been diagnosed to be in need of the low-pressure fuel pump, fuel strainer, fuel meter or fuel tank replacement. If you have a vehicle that match the qualifiers listed below, AHM requests to have the photos of the lock ring & the low-pressure fuel pump flange taken & sent to TIS (click HERE for example photos).
NHTSA #11005271 - FUEL/PROPULSION SYSTEM Jul 6, 2024
Dealer Message - Dealer Message - American Honda Motor Co., Inc. (AHM) is searching for certain 2018-2020 Accords, 2016-2020 Civics, 2017-2020 CR-Vs, & 2018-2020 Odysseys that have been diagnosed to be in need of the low-pressure fuel pump, fuel strainer, fuel meter or fuel tank replacement.
NHTSA #11004264 - VISIBILITY/WIPER Jun 19, 2024
Service Bulletin - Due to a new North America regulation which introduces a new refrigerant and oil requirement, the compressor shaft seal may leak. American Honda is extending the warranty on the A/C compressor shaft seal from the original 3 years to 10 years from the original date of purchase, with no mileage limitation. The new refrigerant and oil may cause swelling of the compressor shaft seal. The swelling may lead to abnormal wearing of the seal which may increase seal gaps around the compressor shaft allowing refrigerant to leak out.
NHTSA #11002711 - VISIBILITY/WIPER Jun 19, 2024
Service Bulletin - American Honda is extending the warranty on the A/C condenser to 10 years from the original date of purchase with unlimited miles. This warranty extension only covers vehicles that have a defective A/C condenser from the factory. The A/C condenser was not manufactured to specification. As a result, corrosion may develop in the form of tiny holes in the condenser tube walls that allow the refrigerant to leak out.
NHTSA #11002705
+14 more TSBs available in MECH AI's TSB explorer for this vehicle.
NHTSA complaints & recalls for the 2017 Honda Civic
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 Honda Civic. Use these to gauge how common a problem is on your specific vehicle before you start chasing Honda Civic diagnostics.
- ENGINE 65
- STEERING 161
- UNKNOWN OR OTHER 160
- ELECTRICAL SYSTEM 99
- SERVICE BRAKES 35
6 active recalls
- STEERING:ELECTRIC POWER ASSIST SYSTEM Sep 2018
Honda (American Honda Motor Co.) is recalling certain 2017-2018 Honda Civic and CR-V vehicles. The magnet that controls the torque sensor output signal for the electronic power steering system may not be properly secured, allowing the magnet to become dislodged. During a full…
NHTSA campaign 18V663000 - EQUIPMENT:OTHER:OWNERS/SERVICE/OTHER MANUAL Nov 2018
Honda (American Honda Motor Co.) is recalling certain 2017-2018 Honda Civic Hatchback and Civic Type R vehicles. The owners guide in these vehicles may not have been included or if included, the owner's guide may not have been properly provided required information. As such, t…
NHTSA campaign 18V817000 - AIR BAGS Apr 2018
Honda (American Honda Motor Co.) is recalling certain 2017 Honda Civic Hatchback and Civic Type R vehicles. Driver and front passenger seatback pads sold as replacement service parts were made without slit openings for the seat-mounted side air bags. In the event of a crash nece…
NHTSA campaign 18V266000 - POWER TRAIN:DRIVELINE:DRIVESHAFT Nov 2017
Honda (American Honda Motor Co.) is recalling certain 2017 Honda Civic Sedan and Coupe vehicles. The right halfshaft may have been improperly heat treated, reducing its strength.…
NHTSA campaign 17V706000
How do I fix P0121 on a 2017 Honda Civic?
- Clean the throttle body with throttle-body-safe cleaner
- Perform a throttle / idle relearn procedure
- Replace the TPS or the electronic throttle body assembly
- Repair damaged TPS connector or wiring
About the 2015-2019 Honda Civic
The 2015-2019 Honda Civic was commonly sold with the following powertrains: 2.0L I4, 1.5L Turbo I4, 1.8L I4. Common trims include LX, Sport, EX, Touring.
When P0121 means “clean the throttle body” vs “replace the throttle body”
Approximately half of P0121 cases on vehicles over 80,000 miles resolve with a throttle body cleaning and relearn. The other half require sensor or assembly replacement. The deciding test: after cleaning, does the TPS voltage sweep smoothly from closed to wide-open without glitches? If yes, the part is good. If no, replace.
Direct-injection engines and throttle body coking
Direct-injection engines (which inject fuel directly into the cylinder, bypassing the intake) build up carbon on the back of intake valves AND on the throttle body. Coking on the throttle body causes the blade to close incompletely, which sets P0121 even with a perfect sensor. Cleaning becomes part of routine maintenance on these engines, often required every 30–50k miles.
Why P0121 needs a relearn after the fix
Modern electronic throttle systems memorize the closed-throttle position as a calibration point. When the throttle body is cleaned, removed, or replaced, the stored position no longer matches reality. A relearn procedure tells the ECM to re-record the new closed position. Without it, the engine may idle high, surge, or set P0121 again within a few drive cycles.
P0121 on a 2017 Honda Civic: frequently asked questions
What does diagnostic trouble code P0121 mean on a 2017 Honda Civic?
P0121 is set when the engine control module sees the throttle position sensor signal moving outside its expected range or changing in a way that does not match other inputs (MAP, MAF, engine load). The TPS reports where the throttle blade is — inputs like accelerator pedal position, engine load, and idle control all depend on accurate TPS readings. Bad TPS data triggers reduced-power or limp mode on many vehicles.
What are the symptoms of P0121 on a 2017 Honda Civic?
Check Engine Light is illuminated. Throttle hesitation or surging at light pedal input. Stalling when coming to a stop. Reduced engine power / limp mode. Erratic or hunting idle. Slow or absent throttle response. On electronic-throttle vehicles, may set ETC fault / wrench icon
What causes P0121 on a 2017 Honda Civic?
Worn throttle position sensor (mechanical TPS wear) (most-common). Carbon buildup in the throttle body causing the blade to bind (common). Corroded TPS connector or damaged signal wiring (common). Failed electronic throttle body (combined ETB / TPS unit) (common). TPS sensor needs reset / relearn after battery disconnect (occasional). Damaged accelerator pedal position sensor (separate code in some cases) (occasional). PCM input fault (rare) (rare)
Is it safe to drive a 2017 Honda Civic with P0121?
In most cases a 2017 Honda Civic stays drivable for short trips with P0121 active, but it should be diagnosed and repaired promptly — this is a high-severity code. Ignoring it can lead to further damage or a failed emissions test.