This tutorial will show you how to test the throttle position sensor on the 2002-2005 vehicles equipped with the 2.2L GM Ecotec engine. These vehicles are the: Chevrolet Cavalier and Classic, Oldsmobile Alero, and the Pontiac Grand Am and Sunfire.
The throttle position sensor test is a multimeter test, so you don't need a scan tool. In case you're wondering, the TPS test consist of making sure the sensor is creating a throttle angle voltage signal, and that it's getting power and ground.
With the results of this test, you'll be able to find out if the throttle position sensor is bad or not.
Contents of this tutorial:
Symptoms Of A Bad Throttle Position Sensor
As you're probably already aware, the air that the engine breathes passes across the throttle plate. The throttle plate is connected to the accelerator pedal via the accelerator cable.
When your foot is off the accelerator pedal, the throttle plate is in its closed position. This restricts the amount of air that's entering the engine. Now, when you step on the accelerator pedal, the throttle plate starts to open. This also causes more air to enter the engine. The fuel injection computer has to inject more fuel to compensate for the additional air entering the engine.
Although the TPS is not the component that measures the air entering the engine, the fuel injection computer needs to know the exact position of the throttle plate (as you step on or off the accelerator pedal). This information is used, among many things, to inject more fuel, to advance ignition timing, etc.
Due to the fact that the info the TPS provides the PCM is important, when it fails you'll see or more of the following symptoms:
- One of the following trouble codes lighting up the check engine light (CEL):
- P0121: Throttle Position Sensor.
- P0122: Throttle Position Sensor.
- P0123: Throttle Position Sensor.
- Hesitation when accelerating the engine.
- Lack of power.
- Bad gas mileage.
TEST 1: Testing The TPS Voltage Signal
When a TP sensor fails, it usually stops creating a voltage signal that corresponds to the opening and closing of the throttle plate. In other words, its voltage output signal stays stuck a specific voltage value irregardless of throttle plate position.
Thankfully, you and I can measure this voltage signal, with a multimeter, and see if it's performing like it should. To do this, we need to tap into the TP sensor's middle wire and read its voltage signal as we manually open and close the throttle plate.
If the TPS is working correctly, this throttle angle voltage signal will increase as we open the throttle plate and decrease as we close it.
As I mentioned before, if the throttle position sensor is bad, its throttle angle voltage signal will stay stuck in one voltage value no matter how much we open or close the throttle plate.
Alright, these are the test steps:
Turn the key to the ON position but don't start the engine, and place your multimeter in Volts DC mode.
Probe the wire labeled with the #3 (in the photo above) with the red multimeter test lead.
Ground the black multimeter test lead on 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.
Your multimeter should report a voltage between .2 to .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.
Slowly open the throttle (by hand and from the engine compartment). The voltage numbers 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.
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 3.
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 6 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 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 throttle angle voltage DID NOT increase (or decrease) as you opened and closed the throttle plate. This test result usually tells you that the TPS is bad.
Just to tie up any loose ends, I recommend that you make sure that it's getting both power (5 Volts) and ground. For these tests, go to: TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.
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 and ground, go to TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.