How To Test The Throttle Position Sensor (2002-2005 GM 2.2L)

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.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.2L Chevrolet Cavalier: 2002, 2003, 2004, 2005.
• 2.2L Chevrolet Classic: 2004, 2005.
• 2.2L Oldsmobile Alero: 2002, 2003, 2004.
• 2.2L Pontiac Grand Am: 2002, 2003, 2004, 2005.
• 2.2L Pontiac Sunfire: 2002, 2003, 2004, 2005.

ALTERNATOR DIAGNOSTIC TESTS: How To Test The Alternator (2002-2005 2.2L Ecotec).

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.

Where To Buy The TPS And Save

The following links will help you to comparison shop for the TPS. I think they'll save you a few bucks:

Not sure if the above TPS fits your particular 2.2L Ecotec equipped GM vehicle? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular GM vehicle. If it doesn't fit, they'll find you the right one.

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 regardless 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:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Connect the black multimeter test lead on the battery negative (-) terminal.

3. 3

   Probe the wire labeled with the #3 (in the photo above) with the red multimeter test lead.
   
   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: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

4. 4

   Turn the key to the ON position but don't start the engine.

5. 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.

6. 6

   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.

7. 7

   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.

8. 8

   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.

9. 9

   Repeat step 8 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: Making Sure The TPS Is Getting 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 the next step is to check that the TP sensor is getting power and Ground, go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.

TEST 2: Making Sure The TPS Is Getting 5 Volts

If, in TEST 1, the TP sensor did not produce a variable voltage that reacts to how you open or close the throttle plate, then there's a good chance it may be missing power.

In this test section, we're going to make sure the TP sensor is getting power from the PCM, which comes in the form of 5 Volts DC.

The wire that delivers this voltage to the TP sensor is the one I've labeled with the number 1 in the image above.

To check for the presence of these 5 Volts, we'll do a simple multimeter Volts test on the female terminal that connects to this wire.

Alright, here we go:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter test lead to the battery negative (-) terminal.

4. 4

   Turn the key to the ON position, but don't start the engine.

5. 5

   Probe the female terminal that connects to the wire labeled with the number 1 in the image above.

6. 6

   Your multimeter should register 4.5 to 5 Volts DC, if the sensor is getting power.

Let's take a look at what your test results mean:

CASE 1: 4.5 to 5 Volts are present. This is the expected test result.

Now that we know the TP sensor is getting power, we need to make sure it's also getting Ground. For this next check, head over to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: Power IS NOT present. Make sure you're testing the correct terminal and repeat the test.

If your multimeter still doesn't report 4.5 to 5 Volts DC, then we can exonerate the TP sensor as bad, since without power, it's just not gonna function.

If, after repeating the test, you still don't see the indicated voltage, then we can conclude there's probably an open-circuit issue in the wiring between the TP sensor connector and the PCM connector.

Although it's beyond the scope of this tutorial, your next step is to find out why these 5 Volts are missing from the circuit and restore them. Once the TP sensor gets its power back, you'll see the TPS issue and diagnostic trouble code go away.

TEST 3: Making Sure The TPS Is Getting Ground

So far, your previous two TPS diagnostic tests have confirmed the following:

• No variable TP sensor signal —The voltage does not increase or decrease as you open and close the throttle plate (TEST 1).
• TP sensor has power —You've confirmed it's getting its 5 Volts (TEST 2).

The final thing we've got to do is make sure the TP sensor is getting Ground, which comes directly from your vehicle's fuel injection computer (PCM).

The wire that delivers this PCM-supplied Ground is the one I've labeled with the number 2 (see photo above).

We'll do a simple multimeter voltage test on the terminal of the connector that connects to this wire to check for the presence of Ground.

NOTE: Be very careful not to apply battery 12 Volts to this wire, or you run the risk of deep frying the PCM. The multimeter voltage test I'm outlining below is a safe way to check for the presence of Ground in this circuit.

Let's get going:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the red multimeter test lead to the battery positive (+) terminal.

4. 4

   Turn the key to the ON position, but don't start the engine.

5. 5

   Probe the female terminal that connects to the wire labeled with the number 2 with the black multimeter test lead (see the image above).

6. 6

   Your multimeter should register 10 to 12 Volts DC, if the sensor is getting Ground from the PCM.

Let's find out what it all means:

CASE 1: Your multimeter registers 10 to 12 Volts DC. This is the expected test result.

We can conclude that the TP sensor is fried and needs to be replaced, but only if you've confirmed the following:

• TP sensor signal is stuck —The voltage stays at one value regardless of throttle plate position (TEST 1).
• TP sensor has power —You've confirmed it's getting its 5 Volts (TEST 2).
• TP sensor has Ground —In this test section, you've confirmed it's getting Ground from the PCM.

CASE 2: Ground IS NOT present. Make sure you're testing the correct female terminal of the connector and repeat the test.

If your multimeter still doesn't show 10 to 12 Volts, then we can conclude the TP sensor isn't getting Ground from the PCM —and without it, it's just not gonna function.

If, after repeating the test, you still don't see the indicated voltage, then we can exonerate the TP sensor as bad and conclude there's an open-circuit issue in the wiring between the TP sensor connector and the PCM connector.

Now, it's beyond the scope of this tutorial to find out why this Ground is missing, but your next step is to troubleshoot the issue and restore Ground to the circuit. Once the TP sensor has Ground, you'll see the TPS issue resolved and the diagnostic trouble code go away.