The throttle position sensor (TPS) is probably one of the easiest engine management system components to test on your 2.5L Chevy S10 pickup or GMC S15 pickup.
The good news is that testing the TPS doesn't require expensive diagnostic equipment, or even a scan tool.
In this tutorial, you'll find the three multimeter tests you need to perform on the TPS to find out if it's good or bad.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1987, 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Symptoms Of A Bad Throttle Position Sensor
The fuel injection computer needs to know when you step on the gas pedal and when you release it.
This is because when you step on the gas pedal, the throttle plate opens and allows more air into the engine. When you release the accelerator pedal, less air gets into the engine.
As more or less air enters the engine, the fuel injection computer must inject more or less fuel into the cylinders.
The component of the engine management system tasked with reporting the throttle angle to the fuel injection computer is the throttle position sensor.
When the TPS fails, you'll see one of the following TPS diagnostic trouble codes illuminating the check engine light:
- Code 21: Throttle Position Sensor (TPS) Signal Voltage High.
- Code 22: Throttle Position Sensor (TPS) Signal Voltage Low.
You'll also see one or more of the following symptoms:
- Hesitation when accelerating the engine.
- Lack of power.
- Bad gas mileage.
- Engine is hard to start.
- Engine idle is too low and the engine stalls.
- Engine idle is too high.
Where To Buy The TPS And Save
The throttle position sensor is not an expensive component, but it doesn't hurt to save money and here are recommendations from well-known automotive brands (avoid knock-off sensors).
Not sure if the above TPS fits your particular vehicle? Don't worry. Once you get to the site they'll make sure it fits by asking you the specifics of your particular vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Testing The TPS Voltage Signal
As you probably already know, the TPS generates a variable voltage signal. This voltage signal corresponds to the amount that the throttle plate opens or closes.
When the TPS fails, it usually stays stuck producing a single voltage value regardless of the position (angle) of the throttle plate.
So for our first test, we'll check the TPS voltage signal and see if it responds to throttle plate movement.
The wire that you'll connect your multimeter to is the blue (BLU) wire of the sensor's 3-wire connector and it connects to the female terminal labeled with the letter C in the illustration above.
NOTE: You'll need a multimeter to be able to test the throttle position sensor. If you don't have one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
OK, let's start:
PART 1:
- 1
Turn the key to the ON position but don't start the engine.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the red multimeter test lead to the blue (BLU) wire of the TP sensor harness connector.
The BLU wire connects to the terminal identified with the letter C in the photo above. - 4
Connect the black multimeter test lead to the battery negative (-) terminal.
NOTE: The TP sensor must remain connected to its electrical connector. You'll need to use a back probe or a wiring piercing probe to tap into the signal of the wire. To see what a wire piercing probe looks like and where to buy one, go here: Wire Piercing Probe. - 5
Your multimeter should report a voltage between 0.2 to 0.9 Volts DC with the throttle plate closed.
If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
PART 2:
- 6
Slowly open the throttle plate (by hand from the engine compartment).
- 7
The voltage value should increase as the throttle plate opens.
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. - 8
Slowly close the throttle plate.
- 9
As the throttle plate is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the same voltage you noticed in step 5.
PART 3:
- 10
Lightly tap on the throttle position sensor with the handle of a screw-driver or something similar (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. - 11
Repeat step 10 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: The TPS signal voltage increased/decreased as you opened/closed the throttle plate. This is the correct test result and it lets you know the TPS is functioning correctly.
You can also conclude that the TPS is receiving power and Ground. No further testing is needed.
CASE 2: The TPS signal voltage DID NOT increase/decrease as you opened/closed the throttle plate. This test result usually tells you the TPS is bad.
To be sure the TPS is bad, you need to make sure it's getting power and Ground. Go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This usually indicates one of two things: the TPS is bad or it's not getting power or Ground.
For the next test, go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
