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P0121 Code: Causes, Symptoms and Ways to Fix It! 

  • Cars Explained
  • Gerard Stevens
  • 7 minutes

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Modern cars depend heavily on a network of modules, intelligent devices, and wiring for safe and efficient operation. Nevertheless, despite front-line manufacturing techniques, no vehicle is safe from an occasional electrical failure. These defects can range in severity, resulting in anything from check engine light to significant issues with the car’s drivability. P0121 code is one such diagnostic trouble code that identifies an electrical fault that can reduce the overall reliability of your car.  


Be mindful that your car’s Throttle Position Sensor (TPS) “A” Circuit has issues when the engine code P0121 appears. It is one issue that will be difficult to solve if it occurs. This issue can also result in intermittent knocking and even vehicle stalling. So, what leads to the P0121 code? What are its symptoms? How can you rectify it? We’ve all that info covered for you! 

What does code P0121 mean? 

The definition of the code means Throttle Position Sensor (TPS) “A” Circuit Range Performance Problem. Your car’s TPS ‘A’ Circuit, like the TPS’ B’ Circuit, has an anticipated output voltage range (if so equipped). When code P0121 appears, it hints that the Engine Control Module (ECM) has detected that the predicted output voltage of the TPS ‘A’ circuit has gone above or below the sensor’s expected range. When the code activates, your car’s ECM will enter failsafe mode. It could result in limited speeds or acceleration, depending on your car’s failsafe system. In some situations, the car will be unable to drive to the repair and will require towing. 

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What causes a P0121 code? 

P0121 diagnostic trouble code appears due to a variety of problems, some of which are more common than others. Being aware of the possible reasons for the code will help speed up the diagnostic process. These are some of the most common reasons why the code appears. 

  • Defective throttle body 
  • Unclean throttle body  
  • A defective Throttle Position Sensor (TPS) 
  • Throttle position sensor improperly connected 
  • Presence of corroded pins in throttle position circuit-related connectors 
  • TPS circuit that is open or shorted 

Symptoms of P0121 code 

Many additional symptoms are frequently associated with the P0121 code. While not all of these symptoms will be present in every case, the majority of the issues will show up in any car having this diagnostic trouble code. These are some of the most frequent symptoms you can observe when this code shows up.  

  • Check Engine Light turns on 
  • Stalling 
  • Having starting troubles 
  • Inadequate throttle response 
  • Inconsistent acceleration  
  • Reduction in engine power 

How serious is the P0121 code? 

Due to its potential consequences on a car’s drivability, the P0121code is generally viewed as being highly serious. Many serious drivability-related symptoms frequently accompany the P0121 code, which can pose a risk to your ability to travel safely and efficiently. 


Stalling, reduced engine power, and inconsistent acceleration are some of the most serious symptoms connected with this engine code. So, in most severe cases, the appearance of the code can leave you stranded. In any case, you need to identify the main cause of the code and fix it as soon as possible. If you can’t fix the issue on your own, make an appointment with your nearest service facility at the earliest.  

Can I drive with the P0121 code? 

You can technically drive with a bad throttle position sensor. A malfunctioning throttle position sensor, on the other hand, can result in an inability to shift up, a rough or slow idle, and a lack of power when accelerating. However, it is best to stop driving immediately when the code shows up. You need to fix the issue at the earliest to avoid getting stranded.  

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How to diagnose P0121 code 

These are some steps followed by the mechanic to diagnose the engine code.  

  • Scanning and recording the codes received, as well as looking at the freeze frame data to see when the P0121 code got set. 
  • Clear the OBD-II fault codes and test the car again to determine whether the P0121 code reappears. 
  • Visually check all TPS connections and wiring for any loose or broken components. 
  • Compare data from TPS circuits A and B on the scanner. If necessary, execute TPS pinpoint tests as directed by the manufacturer. 

Common mistakes made while diagnosing the code 

  • Initially, not performing a visual inspection 
  • Not scanning, recording, clearing, or retesting to verify the codes 
  • Replacing the TPS sensor before correctly diagnosing the issue 
  • Not comparing the parameters of TPS sensors A and B before and after repairs or replacements 

How to fix code P0121 

To find and fix the main cause of diagnostic problem code P0121, follow the instructions below. Before performing any repairs, always consult the factory-specific service documentation for your car’s make and model. 

Look For More DTCs 

Check for additional diagnostic fault codes before starting the diagnostic process. Any such error codes need to be thoroughly diagnosed and corrected before proceeding. 

Visually examine the TPS/Wiring 

The fixing process starts with a visual inspection of the throttle position sensor and its connections. Repair the damaged or frayed wires, while TPS or throttle body damage may require replacement. You need to also check The TPS connector pins for consistency. 

Clean the throttle body 

Then clean the engine’s throttle body to remove carbon fouling. Using a rag saturated with a throttle body cleaner will do the trick. Electrically operated throttle bodies must be removed for cleaning thoroughly. Following the treatment, some electronic throttle bodies require recalibration. 

Test the voltages between circuits  

You need to conduct a test to find an open or shorted circuit if DTC P0121 persists. When evaluating a mechanical throttle body, use a multimeter, and when testing an electronically controlled throttle body, use a quality scan tool. Then compare all the data to the manufacturer’s lowest and maximum values. If the TPS has power/ground but is ‘open’ or ‘grounded,’ replace the sensor.  

What repairs can fix the P0121 code? 

Do these repairs to fix the engine code error.

  • Repair or replace the TPS connector 
  • Do wiring repairs if required 
  • Do a replacement for TPS with a new sensor 

Things to consider while doing the repair 

  • You may need to do additional repairs to get a complete fix as the P0121 code may be accompanied by other TPS codes. 
  • A defective TPS sensor not tracking the throttle angle can lead to most P0121 failures.  
  • All TPS codes force the ECM to move to failsafe mode. 
  • All TPS codes have nearly the same drive symptoms. 

How much does it cost to fix code P0121? 

To fix the P0121 code, you may require one or more of the following repairs. The estimated cost of repair includes the cost of components and labor for each conceivable repair. The repair cost will vary based on your location and car type. 

Item  Estimated cost 
TPS  $170-$230 
Throttle body cleaning  $220-$290 
Throttle body  $580-$690 
Wiring repair/replacement  $100-$1000 

The bottom line 

  • The appearance of the P0121 code indicates that there is an issue with Throttle Position Sensor (TPS) “A” Circuit. 
  • It is better to stop driving immediately when your car encounter this issue. 
  • Try to fix ix this code immediately (same-day if possible) to avoid getting stranded. 
  • When diagnosing the P0121 code, it is critical to follow the entire diagnostic process. A defective throttle position sensor (TPS), a bad or faulty throttle body, or damaged TPS cables might cause this DTC. 

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