P0121
Fix within a few daysYour engine computer detects that the Throttle Position Sensor (TPS) or Pedal Position Sensor (PPS) signal is outside its expected range for the current throttle opening or pedal input.
Code P0121 means your Throttle Position Sensor (TPS) signal is out of expected range. Common causes: Faulty TPS (70%), wiring issues (20%), dirty throttle body (8%). Drivability: Yes, for short trips. Repair cost: $40-$160 DIY, $130-$400 professional.
Can I Drive With P0121?
Yes, for short trips only
Essential trips under 10 miles, avoid highways and heavy traffic. Be prepared for potential stalling or power loss.
Stop driving immediately if: Engine stalls repeatedly, significant power loss, or the check engine light starts flashing.
Symptoms of P0121
- 1Engine hesitation or surging during acceleration
- 2Rough or erratic idle
- 3Poor acceleration or lack of power
- 4Engine stalling, especially when coming to a stop
- 5Vehicle entering 'limp mode' (reduced power)
- 6Unresponsive accelerator pedal
Common Causes of P0121
Parts most likely causing this code, ranked by probability
The sensor itself is faulty, sending an incorrect voltage signal to the engine computer.
70% of P0121 cases are fixed by replacing this part
Damaged, corroded, or loose wiring and connectors to the TPS/PPS can cause intermittent or incorrect signals.
20% of P0121 cases are fixed by repairing wiring or connectors
Excessive carbon buildup can prevent the throttle plate from moving smoothly, or the electronic throttle body (which often integrates the TPS) is failing.
8% of P0121 cases are fixed by cleaning or replacing the throttle body
A rare but possible cause where the computer itself is misinterpreting the sensor signal or has an internal fault.
2% of P0121 cases are fixed by replacing the ECM/PCM
Check These First (Before Buying Parts)
- Visually inspect the TPS/PPS electrical connector and wiring harness for any signs of damage, fraying, corrosion, or loose connections.
- Check for excessive carbon buildup inside the throttle body, especially around the throttle plate. Use throttle body cleaner if necessary.
How to Diagnose P0121
- 1Visually inspect the TPS/PPS sensor and its electrical connector for any signs of damage, corrosion, or loose connections.
- 2Check the throttle body for excessive carbon buildup around the throttle plate, which can impede its movement.
- 3Using an OBD-II scan tool, monitor the live data for the TPS/PPS voltage readings while slowly pressing and releasing the accelerator pedal. Look for smooth, consistent voltage changes without drops or spikes.
- 4With the ignition on (engine off), use a multimeter to test the voltage output of the TPS/PPS at various throttle positions. Compare readings to service manual specifications.
- 5If the vehicle has an electronic throttle body, check for proper operation by observing the throttle plate movement as the pedal is pressed.
P0121 on Popular Vehicles
Toyota Camry
2007-2024Camrys are prone to carbon buildup in the throttle body, which can cause P0121 by restricting smooth throttle plate movement. A failing TPS is also common, often requiring replacement of the entire electronic throttle body assembly.
75% fixed by cleaning or replacing throttle body/TPS
Honda Accord
2003-2024Honda Accords frequently experience P0121 due to a faulty Throttle Position Sensor. On many models, the TPS is part of the electronic throttle body, so the entire unit needs replacement. Wiring harness issues are less common but should be checked.
70% fixed by replacing TPS/throttle body
Ford F-150
2004-2024Ford F-150s, especially those with electronic throttle bodies, often trigger P0121 due to issues with the throttle body assembly itself. This can be due to internal sensor failure or mechanical wear. Cleaning the throttle body is a good first step, but replacement is often necessary.
80% fixed by replacing throttle body
Frequently Asked Questions
What does P0121 mean?
P0121 indicates that your vehicle's engine computer has detected an issue with the signal from the Throttle Position Sensor (TPS) or Pedal Position Sensor (PPS), meaning the signal is outside the expected voltage range for the throttle's actual position.
Can I drive with P0121?
Yes, for short trips only. You can drive your vehicle for essential, short trips, but you should fix this code within a few days. Ignoring it can lead to unpredictable engine behavior, stalling, or the vehicle entering 'limp mode,' which significantly reduces power.
Will P0121 clear itself?
No, P0121 will not clear itself. The engine computer stores this code because it detects a persistent range or performance issue with the throttle position sensor. The code will remain until the underlying problem is diagnosed and repaired.
How do I fix P0121 myself?
Start by visually inspecting the TPS/PPS wiring and connector for damage. Then, check the throttle body for carbon buildup and clean it if necessary. If those don't resolve the issue, you will likely need to replace the Throttle Position Sensor itself. On many modern vehicles, the TPS is integrated into the electronic throttle body, requiring replacement of the entire assembly.
How much does it cost to fix P0121?
A DIY fix for P0121 typically costs $40-$160 for a new TPS or throttle body cleaner. If you take it to a professional mechanic, expect to pay $130-$400, which includes parts and 1-2 hours of labor.
P0121 keeps coming back - why?
If P0121 keeps returning, it points to an incomplete diagnosis. Common reasons include underlying wiring issues that were not fully resolved, a faulty electronic throttle body (if only the sensor was replaced), or, in rare cases, a problem with the engine computer itself. Ensure all connections are secure and clean.
Will P0121 fail emissions/smog test?
Yes, P0121 will cause your vehicle to fail an emissions or smog test. A check engine light illuminated for this code indicates an issue with a critical engine management sensor, which prevents the vehicle from passing inspection.
What's the difference between P0121 and P0122?
P0121 indicates a 'range/performance' problem, meaning the TPS signal is inconsistent or outside the expected operating range. P0122 indicates a 'low input' problem, specifically meaning the TPS signal voltage is consistently too low.
P0121 on Honda Accord
On Honda Accords, P0121 is frequently caused by a failing Throttle Position Sensor, which is often integrated into the electronic throttle body. Carbon buildup on the throttle plate is also a common contributor, leading to erratic sensor readings. Cleaning the throttle body and inspecting wiring are good first steps.
Questions to Ask Your Mechanic
Did you check the live data for the TPS/PPS voltage readings across the full range of throttle movement?
Good answer: Yes, I monitored the voltage and saw a consistent drop or spike at a certain point, indicating an internal sensor fault or a wiring issue.
Have you inspected the throttle body for carbon buildup or any mechanical binding?
Good answer: Yes, I found significant carbon buildup around the throttle plate, which was preventing smooth operation. After cleaning, the readings are now stable.
Repair Cost Estimate
DIY Repair
Parts only
$40-$160
Shop Repair
Parts + labor
$130-$400
Save $90-$240 by doing it yourself
Difficulty
intermediate
Time
0.5-2 hours
Intermediate - Requires an OBD-II scan tool and potentially a multimeter for accurate diagnosis, along with basic hand tools for replacement.
Cost of Waiting
Ignoring P0121 can lead to unpredictable engine behavior, including sudden loss of power, stalling, or the vehicle entering 'limp mode,' which can be dangerous. Continued erratic fuel delivery can also put stress on your catalytic converter, potentially leading to a $1,200-$2,500 replacement.
While You're In There...
If you are removing the air intake tube to access the throttle body, it's a convenient time to inspect and replace the air filter if it's dirty.
If you remove the entire throttle body for cleaning or replacement, installing a new gasket ensures a proper, airtight seal.
While the air intake system is open, cleaning the Mass Air Flow (MAF) sensor can improve overall engine performance and fuel economy.
Tools You'll Need
- OBD-II scan tool
- Multimeter
- Basic hand tools (screwdriver set, socket set)
- Throttle body cleaner
P0121 is a common sensor code that often points to a failing Throttle Position Sensor or a dirty throttle body. Most repairs are straightforward and will restore smooth engine operation.
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Your Next Steps
Step 1: Perform a thorough visual inspection of the TPS/PPS wiring and connector. Look for any signs of damage, corrosion, or loose pins. Clean any corrosion with electrical contact cleaner.
Step 2: Inspect the throttle body for carbon buildup. If present, clean the throttle body thoroughly with throttle body cleaner and a brush. Reassemble and test.
Step 3: If the issue persists, use an OBD-II scan tool to monitor the TPS/PPS live data. If the voltage readings are erratic or outside specifications, you will likely need to replace the Throttle Position Sensor. On many vehicles, this means replacing the entire electronic throttle body assembly.