How To Test The TPS (1991 3.9L V6 Dodge Ram Van)

TEST 2: Making Sure The TPS Is Receiving 5 Volts

There is a good chance that the reason that the TP sensor's voltage signal is stuck in one value (TEST 1) is because it's not getting power.

For our second test, we'll check that the violet with white stripe (VIO/WHT) wire of the TP sensor connector supplies a voltage between 4.5 and 5 Volts DC.

The VIO/WHT wire connects to the female terminal labeled number 1 of the sensor's 3-wire connector (see illustration above).

To check that the VIO/WHT wire is delivering 5 Volts, we're gonna do a simple multimeter voltage test on its connector terminal.

These are the test steps:

1. 1

   Select Volts DC mode on your multimeter.

2. 2

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

3. 3

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

4. 4

   Disconnect the TP sensor from its connector.

5. 5

   With the red multimeter test lead, gently probe terminal 1 of the TP sensor's 3-wire connector.
   
   Confirm that the VIO/WHT connects to terminal number 1.
   
   NOTE: Be careful not to damage the female terminal.

6. 6

   The multimeter should display 4.5 to 5 Volts DC.

Let's interpret your test results:

CASE 1: 4.5 to 5 Volts are present. This means that TPS is getting power and it's what we want to see.

For our final test, we'll check that the TPS is getting Ground. Go to: TEST 3: Making Sure The TPS Is Receiving Ground.

CASE 2: 4.5 to 5 Volts ARE NOT present. Without power, the TP sensor won't generate its variable voltage signal.

The most likely cause of these missing 5 Volts are:

• An open-circuit problem in the wiring connecting the TP sensor 3-wire connector and the fuel injection computer's connector.
• In rare cases, the issue is due to an internal fault in the computer.

Although troubleshooting these missing 5 Volts falls outside this tutorial's scope, you now know the TP sensor itself is OK. Your next step is to resolve the issue causing this voltage to not reach the sensor.

TEST 3: Making Sure The TPS Is Receiving Ground

So far, your previous two test have:

• TEST 1: The TPS voltage signal doesn't increases/decreases when you open/close the throttle plate.
• TEST 2: Power is being delivered to the TP sensor.

In this last test section, we'll confirm that the black with light blue stripe (BLK/LT BLU) wire is delivering Ground to the TP sensor.

The terminal that delivers Ground to the sensor is the one I've labeled with the number 3 in the illustration above.

Terminal number 3 corresponds to the BLK/LT BLU wire of the TP sensor's 3-wire connector.

We'll use a multimeter voltage test to verify that the BLK/LT BLU wire delivers Ground.

NOTE: Ground is provided to the sensor by the fuel injection computer. Be careful not to directly connect this circuit to battery 12 Volts, or you'll fry the computer. The multimeter voltage test I'm suggesting in the instructions is a safe way to check for Ground in this circuit.

These are the test steps:

1. 1

   Select Volts DC mode on your multimeter.

2. 2

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

3. 3

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

4. 4

   Disconnect the TP sensor from its connector.

5. 5

   With the black multimeter test lead, gently probe terminal 3 of the TP sensor's 3-wire connector.
   
   Confirm that the BLK/LT BLU connects to terminal number 3.
   
   NOTE: Be careful not to damage the female terminal.

6. 6

   The multimeter should display 10 to 12 Volts DC if Ground is present.

Let's interpret your test results:

CASE 1: Ground is present. This is the correct test result.

The TPS is faulty and requires replacement if you confirmed all of these conditions:

• The TP sensor does not generate a voltage signal that changes with throttle plate movement (TEST 1).
• The TP sensor is getting 4.5 to 5 Volts (TEST 2).
• The TP sensor is getting Ground (this test section).

CASE 2: Ground IS NOT present. Verify your connections and check you're testing the correct terminal.

If your multimeter still doesn't read 10 to 12 Volts, the throttle position sensor itself is OK. The reason the sensor is not generating a variable voltage signal is due to this lack of Ground.

Although troubleshooting this missing Ground falls outside this tutorial's scope, you now know the TP sensor itself is OK. Your next step is to resolve the issue causing this lack of Ground.

The most likely causes are:

• An open-circuit problem in the wiring connecting the TP sensor 3-wire connector and the fuel injection computer's connector.
• In rare cases, the issue is due to an internal fault in the computer.

More 3.9L V6 Dodge Ram Van Tutorials

You can find a complete list of 3.9L V6 Dodge Ram van tutorials in this index:

• 3.9L V6 Dodge Ram Van Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Engine Compression (1989-2003 3.9L V6 Dodge Ram Van).
• How To Test For A Blown Head Gasket (1989-2003 3.9L V6 Dodge Ram Van).
• How To Test The Fuel Pump (1992-2003 3.9L V6 Dodge Ram Van).
• How To Test The TPS (1989-1990 3.9L V6 Dodge Ram Van.