DTC P0121 – How To Test a Chevy S10 TPS

DTC P0121 – How To Test a Chevy S10 TPS


Trouble Code P0121 is a On Board Diagnostics malfunction that is indicating a throttle position sensor (TPS) error. The specific wording of this trouble code is Throttle Position Sensor Range/Performance Problem meaning that the signal being sent by your TPS is one that your PCM does not expect.

From either old age or a wiring issue, or in the rare event that the TPS has somehow loosened this trouble code is easy to diagnose and fix. Today I’ll be showing you how to test a Chevy S10 TPS in a 2000 Chevy S10 truck. This truck has the GM 2.2 liter engine Vortec 2200 four cylinder engine.

The part number for this unit is Chevy #17106809, and if your local dealership or parts store is currently out of this part, you can try a few interchange numbers. Chevy part numbers 17113578 as well as 17123852 both qualify, and you can also cross over to the Isuzu part number 8171135780 or 8171238520.


In order for you to learn how to test a Chevy S10 TPS, you will need to use a multimeter. Not sure what that is or how to use one? Check out our guide here.

Symptoms of OBDII DTC P0121

  • Surging or bucking under throttle
  • No power
  • No throttle control
  • Check engine light

Where is my Chevy S10 TPS?


The Throttle Position Sensor (TPS) is a deflecting potentiometer that’s mounted opposite of your throttle body butterfly. Open your hood and follow your intake pipe until you reach the throttle body. The side opposite of the cable and butterfly, which is facing towards you has the three pin Chevy S10 TPS.


How To Test a Chevy S10 TPS


  1. Start Engine
  2. Allow to warm to operating temperature
  3. Prepare multimeter
  4. Shut off engine

When you are at this stage, carefully measure the voltage at PIN 3 shown below. This is the blue wire and it’s the signal wire for your Chevy S10 throttle body. If you are having difficulty reaching the wire through the isolation, try backpinning the sensor using a paper clip.


Now put the black ground lead of your multimeter to your battery, and the multimeter should read between .5 to .8 volts with the throttle plate closed. If your vehicle is an automatic, make sure it’s in PARK and the parking brake is raised fully. If your vehicle is a manual transmission, make sure it’s in neutral for this section of our how to test a Chevy S10 TPS DIY Guide.

Manually deflect or open the throttle blade by pushing downward on the throttle butterfly. This should open the throttle and swing the TPS fully open to it’s maximum range. Measure the voltage at PIN 3 again, there should be 4.5 to 4.9 volts at this wire now with the throttle open fully. Slowly close the throttle blade by backing off the throttle butterfly, you should see a smooth transition of voltage without any dips or spikes.

Pro Street Replacement Parts


If your findings are out of range, this means that your Chevy S10 TPS has failed. If there is no voltage at PIN 3 then you should take the next two steps by checking for power and ground at the throttle position sensor.

Checking your Chevy S10 Throttle Position Sensor for Power


Now you’ll need to check the throttle position sensor in your vehicle for switched power and ground. Using your multimeter with the black lead on the negative post of your battery, unplug your throttle position sensor. With the sensor unplugged, gently probe the front of the sensor connector at PIN 1 which is a RED wire.

There should be 5 volts of power here with your key set the “ON” position. If you do have power at this wire, check the connector side of PIN 2 for the low reference ground signal.

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If you don’t have power or ground here at these pins, trace the wiring back until you find the broken section of wire or short. Replace or repair the wire in question to restore the normal operation of your Chevy S10 2.2 liter throttle position sensor.

Use a scan tool to remove the OBDII trouble code, and you are ready to rock and roll! You now know how to test a Chevy S10 TPS, if you have any questions about our guide, leave them below!


  1. My Chevy S10 does not bring back voltage at the pin you showed on this page. I have .2 volts with the throttle closed. Can i adjust the tps?

    • Hi Reggie, thanks for reading.

      This voltage is a tad too low for “adjustment” of which your Chevy does not have. You could in theory try to “slot” your TPS holes, so that you can adjust it but it’s a better idea to just replace your bad TPS.

      Don’t forget to clear the code, thanks for commenting and let us know how it turns out!