Electronic Throttle Body Tests (2002-2007 4.2L Chevrolet TrailBlazer)

TEST 4: TPS 2 Resistance Test (Part 2 Of 2)

In this test section, we'll test the resistance between terminal B and terminal D as we open/close the throttle plate.

Terminal B receives 5 Volts DC from your Chevy TrailBlazer or GMC Envoy's fuel injection computer.

Terminal D sends the TPS 2 signal to the fuel injection computer.

If everything's okay with the circuit, the resistance should decrease as you open the throttle plate, and it should increase as you close the throttle plate.

If there's a problem with this circuit, you'll see the resistance value stuck in one value, or gaps in the reading as you open/close the throttle plate.

These are the test steps:

1. 1

   Disconnect the throttle body from its electrical connector.

2. 2

   Place your multimeter in Ohms mode.

3. 3

   Connect one multimeter test lead to terminal B.
   
   NOTE: You'll make all multimeter connections on the male spade terminals of the electronic throttle body itself.

4. 4

   Connect the other multimeter test lead to terminal D.
   
   At this point, I generally see a reading between 2K to 3K Ohms from a good TPS 2.

5. 5

   Slowly open the throttle plate by hand till it reaches its wide-open throttle (WOT) position.

6. 6

   The resistance value should decrease as you open the throttle plate.
   
   At wide open throttle (WOT), I usually see a reading between 900 to 1K Ohms from a good TPS 2.

7. 7

   Slowly close the throttle plate to its closed position.

8. 8

   The resistance value should increase as you close the throttle plate.

9. 9

   Gently push down and completely close the throttle plate.

10. 10

    The resistance value should continue to increase as you completely close the throttle plate.
    
    At this point (the throttle plate pushed down and completely closed) I generally get a reading between 2K to 3K Ohms from a good TPS 2.

Let's examine your test results:

CASE 1: The resistance decreased/increased without any gaps. This is the correct test result.

If TPS 2 has passed TEST 2 and TEST 3, then you can conclude that it's not defective.

Your last test is to test the throttle actuator motor. Go to: TEST 5: Testing The TAC Motor.

CASE 2: The multimeter DID NOT register the indicated resistance values. This lets you know that TPS 2 is bad. You'll need to replace the throttle actuator assembly.

TEST 5: Testing The TAC Motor

For our last test, we'll test the throttle actuator motor.

We'll test its resistance to see if it has suffered an open-circuit or a short-circuit problem.

If the throttle actuator motor is OK, you should see a reading between 2 and 13 Ohms.

Any Ohms reading below 1 Ohm indicates that the throttle actuator motor has suffered a short-circuit internally.

If your multimeter indicates a reading of no continuity, then the throttle actuator motor has suffered an internal open-circuit problem.

These are the test steps:

1. 1

   Disconnect the throttle body 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 to terminal F.

4. 4

   Your multimeter should read continuity.
   
   If the resistance reading is below 1 Ohm, then the motor has an internal short-circuit problem.
   
   If the resistance reading is in the K Ohms range or your multimeter reads OL, then the motor has an internal open-circuit problem.
   
   The resistance reading I've gotten from good throttle actuator motors has been between 2 and 12 Ohms.

Let's examine your test results:

CASE 1: The multimeter registered continuity between terminal E and F. This is the correct test result.

If your 2002-2005 4.2L Chevy TrailBlazer or GMC Envoy's electronic throttle body passed TEST 1 and TEST 2, then you can conclude that the electronic throttle body is OK and not defective.

CASE 2: The multimeter registered 0 Ohms between terminal E and F (or a value very close to it). This lets you know that the TAC motor has an internal short-circuit problem and is defective.

Replace the throttle actuator assembly.

CASE 3: The multimeter reports no continuity between terminal E and F (the letters OL are displayed). This lets you know that the TAC motor has an internal open-circuit problem and is defective.

Replace the throttle actuator assembly.

More GM 4.2L Test Tutorials

If this tutorial was helpful/informative, you can find a complete list of tutorials here: GM 4.2L Index Of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test For A Blown Head Gasket (2002-2009 4.2L Chevrolet TrailBlazer).
• How Often Should I Replace The Spark Plugs? (2002-2009 4.2L Chevrolet TrailBlazer).
• How To Test Engine Compression (2002-2009 4.2L Chevrolet TrailBlazer).
• How To Test APP Sensor 1 And 2 (2002-2003 4.2L Chevrolet TrailBlazer).