How To Test The Throttle Position Sensor (GM 4.3L, 5.0L, 5.7L)

In three simple test steps, you can find out if the TPS sensor on your GM car or pick up or SUV or Van is bad. You don't need a scan tool, since all three of the tests explained in this article are done with a simple multimeter. Every test has step by step instructions that will make diagnosing the TPS on your GM vehicle a breeze.

At the bottom of this page you'll find a complete list of GM cars, pick ups, SUVs and Vans this test article applies to. Also, in this section you'll find the info you'll need to successfully test and troubleshoot your TPS sensor or code.

You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1996-2004 GM 4.3L, 5.0L, 5.7L) (at: autotecnico-online.com).

Symptoms Of A Bad Throttle Position Sensor (TPS)

Beside the check engine light (CEL) being on and driving you nuts, your Chevy or GMC pick up (or SUV or van) may be experiencing one or several of the following symptoms:

1. TPS diagnostic trouble codes (DTCs) stored in the vehicle's computer's memory.
   • P0121:: Throttle Position Sensor Performance.
   • P0122:: Throttle Position Sensor Circuit Low Voltage.
   • P0123:: Throttle Position Sensor Circuit High Voltage.
2. Really bad gas mileage.
3. Transmission does not shift out of second gear.
4. No power as you accelerate the vehicle.
5. Hesitation when you step on the accelerator pedal.

What Tools Do I Need?

You don't need any expensive testing equipment to test the TPS on GM vehicle. You will need:

1. A multimeter (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing).
2. A helper.
3. A repair manual for any remove and replace info you may need that this article does not cover.

Circuit Descriptions Of The GM TPS Sensor

Like the majority of throttle position sensors on modern fuel injected cars and trucks nowadays, the GM TPS is a three wire sensor. Each wire provides a specific type of signal to the TPS or to the PCM (Powertrain Control Module=Fuel Injection Computer). Below are the circuit descriptions of each:

• Circuit labeled 1:
  • Throttle Position (TP) Signal Circuit. Blue wire.
• Circuit labeled 2:
  • Ground Circuit (Provided by PCM internally). Black wire
• Circuit labeled 3:
  • Power Circuit (5 Volts from PCM). Gray wire.

I'm gonna' make one very important recommendation to you when testing the signals of each wire. And that is to not probe the front of the female terminal of the TPS connector. It's best to use a tool to pierce the wire, such as a wire-piercing probe (you can see what one looks like here: Wire Piercing Probe) to get to and test the signal.

One last observation, these three circuits go directly to the PCM. So you need to be careful not to short these wires to power (12 Volts) or you may fry the PCM.

Where To Buy The TPS And Save

The throttle position sensor (TPS) isn't an expensive part, especially if you shop for and buy it online.

The following links will help you comparison shop for the throttle position sensor (TPS):

Not sure if the TPS sensor above fits your particular GM vehicle? Don't worry, once you get to the site they'll make sure it fits and if it doesn't, they'll find you the right one.

How Does The GM TPS Sensor Work?

Knowing how the throttle position sensor works will help you to understand the 'why' and 'how' of the three tests you're gonna' do in this article. So, in a nutshell when you crank and start your GM car or truck or SUV:

1. 1

   The throttle position sensor gets 5 Volts from the Gray wire and Ground from the Black wire. Both of these are provided internally from the PCM.

2. 2

   Once the car or truck starts and is idling and since the throttle is closed, the TPS sends a base throttle position signal of about 0.5 to 0.9 Volts to the PCM on the Blue wire (this voltage will vary slightly on your vehicle but should be within the 0.5 to 0.9 Volts DC).

3. 3

   When you step on the accelerator pedal to get the car or truck moving, the throttle opens causing the TP sensor to increase its voltage signal.

4. 4

   This is how the PCM knows that the throttle just opened up and that it needs to start injecting more fuel and advancing ignition timing, transmission shift points, etc.

5. 5

   As you let go off the gas pedal (accelerator pedal) the throttle closes and the TP sensor decreases the voltage signal to the PCM and returns to its base voltage signal, till you step on the accelerator pedal to move the vehicle and the cycle begins again.

Pretty simple stuff, no? Well testing it is just as simple. Since you'll be working in the engine compartment, no need to tell you (but I'm gonna' tell you anyway) to be alert and be very careful. Use common sense and take all necessary safety precautions.

TPS Diagnostic Manual Download

If you'd like to have access to a wiring diagram, throttle position sensor connector pin-outs, and the entire testing procedure in one place, then take a look at the following:

1996-2000 C/K Series Full Size Pick Ups:

TEST 1: Testing The Throttle Position Sensor Signal

As mentioned at the beginning of the article, the throttle position (TP) signal that tells the PCM how much the throttle plate opens/closes when you step on/off the accelerator pedal.

If the throttle position sensor is working correctly, the multimeter will register a smooth increase in the DC voltage until the maximum voltage is reached, which is about 4.5 Volts DC.

Then, as you slowly release the throttle plate back to its closed position, the multimeter will display a gradual decrease in voltage till the initial base voltage is achieved (which you recorded in the beginning of the test).

If the TPS is bad, the voltage value will stay stuck in one number or there will be sudden gaps/loss of voltage or the readings will jump about crazily as you open/close the throttle plate (especially when you tap on the sensor).

You'll need a helper to assist you in this test step, since he or she will need to lightly tap on the throttle position sensor's body with a screwdriver (or other appropriate tool) while you observe the multimeter and manually actuate the throttle.

NOTE: Start and warm up the engine before testing the TPS signal voltage. Once the engine has reached its operating temperature, turn it off.

IMPORTANT: The throttle position sensor must remain connected to its electrical connector for this test to work. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool and where to buy it here: Wire Piercing Probe.

OK, let's start testing:

PART 1

1. 1

   Place your multimeter still in DC Volts mode.

2. 2

   Connect the red multimeter test lead the wire labeled with the number 1 in the photo. This should be the blue (BLU) wire of the TPS connector.

3. 3

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

4. 4

   Turn the key to its ON position, but DO NOT start the engine.

5. 5

   Your multimeter should register between 0.5 to 0.9 Volts DC. This voltage value should not be jumping up and down but should remain steady.

PART 2

1. 6

   Manually open the throttle plate by hand as you observe the voltage displayed on your multimeter.

2. 7

   The initial voltage reading should increase smoothly as you open the throttle plate to its wide open position.
   
   At wide open throttle, you should see about: 4.5 to 4.9 Volts.

3. 8

   Now, slowly release the throttle plate to its fully closed position, all the while observing the multimeter's reading.

4. 9

   The multimeter's voltage reading should decrease in a smooth and linear fashion and return to the initial voltage reading you observed at the beginning of the test.

PART 3

1. 10

   Have your helper lightly tap the TP sensor with the butt of a screw-driver's handle (or something similar).

2. 11

   Slowly open and close the throttle plate as your helper taps the TP sensor.

3. 12

   The tapping should have NO effect on the multimeter voltage readings.

4. 13

   Repeat this (tapping the throttle position sensor) several times to make sure of your results.

Let's interpret your TPS signal voltage test:

CASE 1: The multimeter registered a smooth increase or decrease in voltage. This test result tells you that the TP sensor on your GM vehicle is working OK and is not the cause of the TPS fault code issue.

If you still have a TPS trouble code lighting up the check engine light, this section will have a few more suggestions as to what could be causing the problem: TPS Code Won't Go Away.

CASE 2: The multimeter DID NOT register a smooth increase or decrease in voltage. This usually means the throttle position sensor (TPS) is bad on your GM car or pick up or SUV.

To be sure the TPS is bad, we need to make sure it's getting both power and Ground. For the first of these two tests, go to: TEST 2: Testing The 5 Volt Reference Signal.