How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 S10/S15)

Testing the throttle position sensor on your 1986-1991 2.8L V6 equipped S10 (or S15) is a pretty simple and straightforward process. The cool thing about the TPS test is that it's done with a simple multimeter... no scan tool needed.

The GM 1986-1991 TPS needs to be adjusted if replaced or mis-adjusted... so, I've also included the TPS adjustment procedure.

The contents of this tutorial at a glance:

  1. Symptoms Of A Bad Throttle Position Sensor.
  2. TEST 1: Testing The Throttle Position Sensor Voltage Signal.
  3. TEST 2: Verifying Throttle Position Sensor Has Power.
  4. TEST 3: Verifying Throttle Position Sensor Has Ground.
  5. How To Adjust the TPS.
  6. Where To Buy Your Throttle Position Sensor And Save.
  7. More GM 2.8L Tutorials.

NOTE: Starting with the 1991 model year, the TPS changed to an updated design. For the 1991 and newer TPS test, go to: How To Test The Throttle Position Sensor (1991-1993 2.8L Chevy S10 Pick Up).

Symptoms Of A Bad Throttle Position Sensor

The TPS is a very important part of the the throttle body fuel injection system... since it reports to the fuel injection computer how much the throttle plate angle as you step on/off the accelerator pedal.

With this info the computer, on your 2.8L S10/S15, can now manage the engine to produce the best performance and lowest possible emissions under all operating conditions.

Being that the TPS is a mission-critical sensor, when it fails your engine performance is going to suffer! You'll also see one or more of the following symptoms:

  1. Check engine light (CEL) illuminated on your Chevy S10's instrument panel.
  2. A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
    1. 21: Throttle Position Sensor Signal Voltage High.
    2. 22: Throttle Position Sensor Signal Voltage Low.
  3. Your 2.8L fails the smog check (state mandated emissions test).
  4. Bad gas mileage.
  5. Hard start and/or extended cranking time (after shut off).
  6. Black smoke coming out of the tailpipe.
  7. Hesitation when accelerating your vehicle down the road.

Thankfully, the TPS can be tested without a scan tool and in the next section we'll start with the very first test.

TEST 1: Testing The Throttle Position Sensor Voltage Signal

How To Test The Throttle Position Sensor (1986, 1987, 1988, 1989, 1990, 1991 S10/S15)

As you're already aware, the accelerator pedal is connected to the throttle plate (on the throttle body) via a cable. This cable is known as the accelerator cable.

As you step on or off the accelerator pedal, the throttle plate opens or closes. It's the throttle position sensor's job to inform the fuel injection computer of these changes in the throttle plate's angle.

The cool thing is that you and I can tap into the voltage signal that the throttle position sensor creates with a multimeter. Thus we can see if it is producing a correct throttle angle voltage signal or not.

The wire that we're going to tap into, to check the throttle plate angle voltage signal, is the dark blue (DK BLU) wire of the TPS connector.

NOTE: The throttle position sensor has to remain connected to its connector for this test to work (this is where a wire piercing probe comes in handy to get to the signal inside the wire. To see what one looks like, click here: Wire Piercing Probe Tool.)

OK, let's start:

  1. 1

    Place your multimeter in Volts DC mode and with the RED multimeter lead probe the DK BLU wire of the sensor's connector. This is the wire that connects to TPS connector terminal letter B in the illustration above.

  2. 2

    Ground the BLACK multimeter test lead on the battery negative terminal. Have you helper turn the Key On, but don't start the engine (this will power up the TP sensor).

  3. 3

    Your multimeter should report a voltage between .2 to .9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.

Part 2

  1. 4

    Now, slowly open the throttle (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.

    For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.

  2. 5

    As the throttle opens, the voltage numbers will increase. This increase in voltage should be smooth and without any gaps or skips. Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.

  3. 6

    Now, slowly close the throttle. As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 4.

Part 3

  1. 7

    OK, now you'll need someone to help you lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle and observe the multimeter.

    If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.

  2. 8

    Repeat step 7 several times to make sure of your multimeter test results.

Let's take a look at your test results:


CASE 1: The throttle angle voltage increased and decreased as you opened and closed the throttle plate. This test result confirms that the TP sensor is OK and not defective.

As a last test, I suggest you check that the TPS is adjusted correctly and producing the correct closed throttle voltage value. For this test, go to: How To Adjust the TPS.

CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This test result confirms that the TPS is behind the TPS trouble code lighting up the check engine light (CEL) on your 2.8L Chevrolet S10.

I'm gonna' suggest that you make sure that the TP sensor is getting both power and ground by performing the last two tests in this tutorial. To check that the TPS is getting power, go to: TEST 2: Verifying Throttle Position Sensor Has Power.

CASE 3: Multimeter DID NOT register any voltage, this test result doesn't condemn the TP sensor as BAD just yet. Why? Because...

... the TP sensor may be missing either power or ground. So the next step is to check that the TP sensor is getting power, go to TEST 2: Verifying Throttle Position Sensor Has Power.