Testing the throttle position sensor (TPS) is not difficult. In this tutorial, I'll explain how you can test it with a multimeter.
You'll easily and quickly determine whether TPS is good or bad with your test results.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1993-1996 2.2L Buick Century, Oldsmobile Cutlass Ciera) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.2L Buick Century: 1993, 1994, 1995, 1996.
- 2.2L Oldsmobile Cutlass Ciera: 1993, 1994, 1995.
- 2.2L Oldsmobile Ciera: 1996.
Symptoms Of A Bad Throttle Position Sensor
As you're probably already aware, the accelerator pedal is connected to the throttle plate (in the throttle body) with an accelerator cable.
The throttle cable causes the throttle plate to open or close as you step on or off the accelerator pedal.
As the throttle plate opens, more air enters the engine, and the fuel injection computer has to increase the amount of fuel it's injecting into it (the engine).
The fuel injection computer becomes aware of the throttle plate angle through the throttle plate angle information provided by the throttle position sensor.
When the throttle position sensor fails, the fuel injection computer will set one of the following diagnostic trouble codes and illuminate the check engine light.
OBD I equipped vehicles:
- 21: Throttle Position Sensor (TPS) Signal Voltage High.
- 22: Throttle Position Sensor (TPS) Signal Voltage Low.
OBD II equipped vehicles:
- P0121: Throttle Position (TP) Circuit Performance Problem.
- P0122: Throttle Position (TP) Circuit Low Input.
- P0123: Throttle Position (TP) Circuit High Input.
You'll also see one or more of the following symptoms:
- Hesitation when accelerating the engine.
- Lack of power.
- Bad gas mileage.
Where To Buy The TPS And Save
The following links will help you to comparison shop for the throttle position sensor of known automotive brands (no 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
The TPS produces a voltage signal that increases as you open the throttle plate and decreases as the throttle plate closes.
Thankfully, we can use a multimeter to confirm that the TPS voltage signal increases/decreases as the throttle plate opens/closes.
Usually, when the TPS fails, it usually stays stuck, producing a single voltage value as the throttle plate opens/closes.
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 (at: easyautodiagnostics.com).
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 is 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 middle 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 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 7 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. It tells you that the throttle position sensor IS NOT defective.
This test result also confirms that the TPS is getting both power and Ground from the fuel injection computer.
CASE 2: The TPS signal voltage DID NOT increase/decrease as you opened/closed the throttle plate. This test result usually tells you that the TPS is bad.
So that you can make 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 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 your next step is to check that the TP sensor is getting power and Ground. Go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
