In this tutorial, I'll show you how to test the throttle position sensor in 3 basic tests that are done with a multimeter. No scan tool or any other expensive diagnostic equipment required.
Also, you don't have to remove the TPS to test it! So, if the check engine light is lit up by one of the following trouble codes: P0121, P0122, or P0123... this tutorial will help you!
The contents of this tutorial at a glance:
- Symptoms of a Bad Throttle Position Sensor.
- TEST 1: Testing the Throttle Position Sensor Voltage Signal.
- TEST 2: Verifying Throttle Position Sensor Has Power.
- TEST 3: Verifying Throttle Position Sensor Has Ground.
- Where to Buy Your Throttle Position Sensor and Save.
- More 2.2L GM Diagnostic Tutorials.
NOTE: The pre-1998 S10/Sonoma throttle position sensor is a different style. It's tested in the exact same way. To see the tutorial that covers the 1995 thru' 1997 throttle position sensor go here: How to Test the Throttle Position Sensor (1995-1997 2.2L S10 and Sonoma).
Symptoms of a Bad Throttle Position Sensor
If you've been wondering what the heck the TPS is for... it's job is to let the PCM know the throttle plate position (angle) as it opens or closes.
This is due to the fact that the throttle plate position constantly changes as you step on (or off) the accelerator pedal (since the accelerator pedal is connected to the throttle plate via a cable).
With the info the TPS provides, the PCM can now: inject more/less fuel, advance/retard ignition timing, calculate automatic transmission shift points, etc.
Since the TPS is such a crucial component of the engine management system... when it fails your 2.2L engine is gonna' resent it. You'll see one or more of the following symptoms:
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- P0121: Throttle Position (TP) Circuit Performance Problem.
- P0122: Throttle Position (TP) Circuit Low Input.
- P0123: Throttle Position (TP) Circuit High Input.
- Your 2.2L Chevy S10 (or GMC Sonoma) 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.
The most important thing to know, when testing the TPS, is that the throttle position signal it produces is a Volts DC signal. This throttle position voltage signal increases as the throttle plate opens and decreases as the throttle plate returns back to its closed position.
With the help of a multimeter, you can very easily verify this increase/decrease in the voltage by tapping into the dark blue (DK BLU) wire, of the TPS electrical connector.
So, for our first TPS test, we're gonna' see if the TPS is creating the correct voltage signal as 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.)
To get this show on the road, this what you'll need to do:
Place your multimeter in Volts DC mode and with the RED multimeter lead probe the DK BLU wire of the sensor's connector.
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).
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.
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: Your multimeter showed the voltage signal increase and then decrease as you opened and closed the throttle plate. This confirms that the TP sensor, on your 2.2L Chevy S10 (or GMC Sonoma) is OK and not defective.
CASE 2: Your multimeter DID NOT show the voltage signal increase and then decrease as you opened and closed the throttle plate. This tells you that the TPS is bad and causing the TPS trouble code lighting up the check engine light (CEL) on your 2.2L Chevy S10 (or GMC Sonoma).
Before you run out and buy it... I'm gonna' suggest that you do two more tests. One is to check that the TPS is getting power. The other is to check that it's ground. To check that the TPS is getting power, go to: TEST 2: Verifying Throttle Position Sensor Has Power.
CASE 3: Your 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.