Testing the throttle position sensor (TPS) on your 1991, 1992, 1993 2.8L Chevy S10 Pick-up can be accurately done with a simple multimeter. In this tutorial I'll show what and how to test it to find out if the TPS is fried or not.
Contents of this tutorial:
NOTE: For the 1986 to 1991 TPS test, go to: How To Test The Throttle Position Sensor (19986-1991 2.8L S10/S15).
Puedes encontrar este tutorial en Español aquí: Cómo Probar El Sensor TPS (1991-1993 2.8L S10 Pick Up) (en: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
The on-board diagnostic (OBD) system on your 2.8L S10 Pickup is designed to light up the check engine light (CEL) when any of the input sensors fail. So, when the TPS fails, the check engine light will light up.
You'll also see one or more of the following symptoms:
- Check engine light (CEL) illuminated on your Chevy S10's instrument panel.
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- 21: Throttle Position Sensor Signal Voltage High.
- 22: Throttle Position Sensor Signal Voltage Low.
- Your 2.8L fails the smog check (state mandated emissions test).
- Bad gas mileage.
- Hard start and/or extended cranking time (after shut off).
- Black smoke coming out of the tailpipe.
- 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
The throttle position sensor's job is to inform the fuel injection computer of the throttle plate's angle as it opens or closes.
The TPS uses power and Ground to create a throttle angle voltage signal. It sends the throttle angle voltage signal to the fuel injection computer thru' the wire that connects to the TPS connector terminal labeled with the letter C in the illustration above.
The first order of business, to see if the TPS is working correctly or not, is to tap into this wire with a multimeter, and see if the TPS is creating a correct throttle angle voltage signal while we manually open and close the throttle plate.
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:
Place your multimeter in Volts DC mode and with the red multimeter test lead probe the middle wire of the sensor's connector. This is the wire that connects to TPS connector terminal letter C in the illustration above.
Ground the black multimeter test lead on the battery negative terminal. Have your helper turn the Key On, but don't start the engine (this will power up the TP sensor).
Your multimeter should report a voltage between 0.2 to 0.9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
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.
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.
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.
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.
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.
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: The 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.