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P0121 – Meaning, Causes, Symptoms, & Fixes

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What Does Code P0121 Mean?

  • P0121 definition: Throttle Position Sensor (TPS) “A” Circuit Range Performance Problem
  • Issue Severity: HIGH – Stop driving immediately.
  • Repair Urgency: Fix this code immediately (same-day if possible) to avoid being stranded.
  • Diagnosis: It is important to complete the entire diagnostic process when diagnosing the P0121 code. This DTC can be triggered by a faulty throttle position sensor (TPS), a dirty or faulty throttle body, or damaged wires in the TPS circuit.

Your TPS “A” Circuit has an expected output voltage range, as does your TPS “B” Circuit (if so equipped). When code P0121 occurs, it means that your Engine Control Module (ECM) recognized that your throttle position “A” circuit’s expected output voltage has either gone above or below the sensor’s expected range. When code P0121 is triggered, your ECM will go into failsafe mode. Depending on the failsafe strategy of your car, this could lead to limited speeds or acceleration. This problem can also cause intermittent knocking and even stalling for your vehicle. In some cases, the car will not be capable of driving to the shop and will need to be towed.

P0121 Causes

  • Faulty Throttle Position Sensor (TPS)
  • Dirty Throttle Body
  • Faulty Throttle Body
  • An open or short of the TPS circuit
  • Bad connection of the TPS connector
  • Corrosion on terminal ends of electrical connections

P0121 Symptoms

  • Check Engine Light
  • Knocking or Jerking
  • Reduced top speed
  • Sluggish acceleration
  • Stalling

How Do I Fix Code P0121?

With a P0121 code, the first step is to get it properly diagnosed to figure out what is causing the malfunction in the coolant temperature circuit. Using the live data function of the FIXD sensor and app allows you to read and analyze inputs from the throttle position sensor and the throttle body temperatures to properly diagnose a P0121 code.

If you’ve tried cleaning the throttle body and checked the wiring for the TPS circuit but you’re not comfortable diagnosing this issue further at home, we recommend finding a RepairPal-certified shop to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

> Find a RepairPal Certified Shop Near You

How Much Does It Cost to Fix Code P0121?

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0121 code.

Possible Repair Costs for P0121

When it comes to making repairs associated with the P0121 code, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair. 

  • Throttle Position Sensor $170-$230
  • Throttle Body Cleaning $220-$290
  • Throttle Body $580-$690
  • Wiring repair/replacement $100-$1000

DIY Steps to Diagnose Code P0121

If you’d like to try to fix code P0121 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Diagnosis can require some specialized equipment beyond what the FIXD Sensor can provide, but, on most vehicles, this is still a beginner-level diagnosis and repair for DIYers. 

DIY difficulty level: Intermediate

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):

STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.

Use FIXD to scan your vehicle to verify P0121 is the only code present. If other codes are present, they must be addressed first.

STEP 2: CHECK WIRING AND CONNECTIONS. 

Inspect all of the connectors for the throttle body and throttle position sensor. If the connectors are in place and don’t show damage, check surrounding wires for evidence of damage.

STEP 3: CLEAN THROTTLE BODY.

Remove the intake pipe from the throttle body. Spray throttle body cleaner on a rag (this rag will get extremely dirty; don’t use one you can’t afford to throw away). Open the throttle body with your hand using the pulley on the side if you have a cable operated system, or push on one side of the throttle plate to push it open. Wipe all the carbon (crusty black substance) off the throttle plate and the throttle body until its fully cleaned. In newer model cars with electronic throttle bodies, you may need to have a throttle body relearn procedure performed after this service.

Tech Tip: DO NOT spray throttle body cleaner into the throttle body. Spraying cleaner directly into the throttle body, instead of onto a rag, can damage the electrical components connected to the throttle body. 

STEP 4: CLEAR CODE AND TEST DRIVE.

After cleaning the throttle body, test drive the vehicle to verify the check engine light stays off. If it is still tripping the code, use a multimeter to check for an open or short in the throttle position sensor. If the TPS fails this test, replace it.

STEP 5: CONSULT A PROFESSIONAL.

If at this point the vehicle is still setting the same code, you may have a more serious problem with your car’s engine coolant system, and you should bring the vehicle to a certified shop to have further diagnostic work performed.  

Common P0121 diagnosis mistakes

It is important to complete the entire diagnostic process when diagnosing P0121. Don’t overlook an easy cause such as a loose connector for the throttle position sensor or a dirty throttle body.

Still Need Help Fixing Code P0121?

If you’ve followed the steps above and are still experiencing issues with the throttle position sensor and code P0121, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.

Jeffrey-Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

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We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.

About the Author

Jeffrey N. Ross

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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