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 a expected output voltage range, as does your TPS “B” Circuit. When code P0121 occurs, it means that your Engine Control Module (ECM) recognized that your “A” circuit’s expected output voltage has either gone above or below the sensor’s expected range when compared to “B” Circuit.

P0121 Symptom

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

P0121 Causes

  • Difference in voltage output between “A” Circuit and “B” Circuit has exceeded 1.6 volts or has gone below .8 volts
  • An open or short of the TPS
  • Bad connection of the TPS
  • Corrosion in connector or sensor

Code P0121 Severity – 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.

Code P0121 Common Diagnosis Mistakes

Failing to conduct a visual inspection of all of the TPS connections to look for any loose or damaged items.

P0121 Diagnosis

 Diagnosis and Repair 

  • A sensor is needed for this next action, and the FIXD sensor is perfect for it. Scan and document the codes received in order to see when the P0121 code was triggered.
  • Check for an open or short in the TPS signal. You will need an oscilloscope to do this.
  • Check all TPS connections visually for loose or damaged items.
  • Compare data between TPS “A” Circuit and “B” Circuit.
  • Repair or replace TPS connector or sensor.
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Comments 1

Gary S.

September 26, 2018

The Regal was from a friend who wanted to sell it to me at a good KBB price. Didn’t buy it. Thanks FIXD!