TEST 2: APP Sensor 1 Resistance Tests (2 Of 2)

How To Test APP Sensor 1 And APP Sensor 2 (2004, 2005, 2006, 2007 4.2L Chevrolet TrailBlazer And GMC Envoy)

In this second APP sensor 1 test, we're going to make sure that the resistance value between terminal E and terminal F decreases as we the depress the accelerator pedal.

Then, as you release the accelerator pedal the resistance value should increase back to the value you noticed at the beginning of the test.

If APP sensor 1 is defective you'll notice one of two things: either the resistance value will stay stuck in one number or it's going to have gaps as you depress/release the accelerator pedal.

These are the test steps:

  1. 1

    Disconnect the APP sensor assembly from its electrical connector.

  2. 2

    Place your multimeter in Ohms mode.

  3. 3

    Connect one multimeter test lead to terminal E and the other test lead to terminal F.

    At this point I generally see a resistance reading of about 3 K Ohms from a good APP sensor 1.

  4. 4

    Slowly depress the pedal by hand till it bottoms out.

    The resistance value should decrease

    With the pedal fully depressed I generally see a resistance reading of about 500 Ohms (0.5 K Ohms) from a good APP sensor 1.

  5. 5

    Slowly release the accelerator pedal.

    The resistance value should increase back to the value (or close to it) that you saw in step 3.

Let's examine your test results:

CASE 1: The resistance decreased/increased smoothly and without gaps as you depressed/released the accelerator pedal. This is the correct test result. If APP sensor 1 passed TEST 1, then you can conclude that APP sensor 1 is working correctly (not defective).

Now that you've confirmed that APP sensor 1 is working correctly, the next step is to test APP sensor 2. Go to: TEST 3: APP Sensor 2 Resistance Tests (1 Of 2).

CASE 2: The resistance DID NOT decrease/increase as you depressed/released the accelerator pedal. With this test result you can conclude that APP sensor 1 is defective. Replace the accelerator pedal.

CASE 3: The resistance decreased/increased BUT there were gaps in the reading as you depressed/released the accelerator pedal. With this test result you can conclude that APP sensor 1 is defective. Replace the accelerator pedal.

TEST 3: APP Sensor 2 Resistance Tests (1 Of 2)

How To Test APP Sensor 1 And APP Sensor 2 (2004, 2005, 2006, 2007 4.2L Chevrolet TrailBlazer And GMC Envoy)

Now that you have confirmed that APP sensor 1 is working correctly, in this test section you're going to start testing APP sensor 2.

Testing APP sensor 2 follows pretty much the same procedure as testing APP sensor 1. The only difference is that you're going to be testing different terminals on the APP sensor assembly.

The terminals that we're going to test are terminal A and terminal C.

Terminal A is one that gets Ground and terminal C is the one that gets 5 Volts. Both Ground and 5 Volts are provided by your Chevrolet Trailblazer or GMC Envoy's fuel injection computer.

What you're looking for is for continuity to be present between these two terminals. If there's a problem between them, your multimeter is going to report either an open-circuit or a short-circuit problem.

If the circuit is open, you're going to see a no continuity reading on your multimeter (usually represented by the letters OL). If there's a short-circuit problem between these two terminals, you're going to see a reading of less than 1 Ohm.

These are the test steps:

  1. 1

    Disconnect the APP sensor assembly from its electrical connector.

  2. 2

    Place your multimeter in Ohms mode.

  3. 3

    Connect one multimeter test lead to terminal A.

  4. 4

    Connect the other test lead to terminal C.

  5. 5

    Your multimeter should read continuity.

    I have usually gotten an Ohms reading of about 3.4 K Ohms at this point when testing a good APP sensor 2.

Let's examine your test results:

CASE 1: The multimeter registered continuity between terminals A and C. This is the expected and correct test result.

The next test is to test the resistance between terminals B and C while you depress/release the accelerator pedal: TEST 4: APP Sensor 2 Resistance Tests (2 Of 2).

CASE 2: The multimeter DID NOT register continuity between terminals A and C. This test result tells you that APP sensor 2 is defective. Replace the accelerator pedal.

Chevrolet Vehicles:

  • Trailblazer 4.2L
    • 2004, 2005, 2006, 2007

GMC Vehicles:

  • Envoy 4.2L
    • 2004, 2005, 2006, 2007