P0121 – Meaning, Causes, Symptoms, & Fixes
Code P0121 Definition
Throttle Position Sensor (TPS) “A” Circuit Range Performance Problem
What Does P0121 Mean?
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.
What Are The Symptoms Of Code P0121?
- Check Engine Light
- Knocking or Jerking
- Reduced top speed
- Sluggish acceleration
What Is The Cause Of Code P0121?
- 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
How Serious Is Code P0121? – High
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.
Code P0121 Common Diagnosis Mistakes
Replacing the TPS or throttle body without attempting a throttle body cleaning.
Tools Needed to Diagnose Code P0121:
How To Diagnose And Repair Code P0121:
Difficulty of Diagnosis and Repair (3 out of 5)
- Check to see if there are any other codes along with P0121 and clear your Check Engine Light with FIXD.
- Check freeze frame data relating to the ECM to help pinpoint the exact issue.
- Check all TPS connections visually for loose or damaged items.
- Try cleaning the throttle body, this is an easy option that your car probably needs anyways. If there’s carbon build up on the throttle plate, it can cause the throttle to stick and send a faulty voltage.
- 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). 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.
- 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.
- Now, test drive the vehicle and see if this fixed the concern.
- If it is still tripping the code, check for an open or short in the TPS sensor. You will need a multimeter to do this. Check out this video for a step by step, if you have a throttle cable system. If you have an electronic throttle body, you would need a diagnostic scan tool for further diagnosis. If the TPS fails this test, replace it.
- If it doesn’t, further diagnostics will need to be done by a reputable shop.
Estimated Cost of Repair
For error code P0121, 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