How To Test The TPS (1991 5.2L, 5.9L V8 Dodge Ram Van)

TEST 2: Making Sure The TPS Is Receiving 5 Volts

If the TP sensor's signal voltage remained stuck during TEST 1, there's a strong possibility it's not receiving the required power.

In this second test, we're going to check whether the violet with white stripe (VIO/WHT) is delivering between 4.5 and 5 Volts DC to the TPS connector.

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

To verify that the VIO/WHT wire is supplying the correct voltage, we'll perform a simple voltage check using a multimeter at the connector terminal.

These are steps to follow:

1. 1

   Set your multimeter to Volts DC mode.

2. 2

   Attach the black test lead to the battery's negative (-) terminal.

3. 3

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

4. 4

   Unplug the TP sensor from its connector.

5. 5

   Use the red test lead to carefully probe terminal 1 of the TPS's 3-wire connector.
   
   Make sure the VIO/WHT wire is the one that connects to terminal 1.
   
   NOTE: Take care not to damage the female terminal when probing.

6. 6

   Your multimeter should show a reading between 4.5 and 5 Volts DC.

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

CASE 1: Voltage is between 4.5 and 5 Volts. This confirms that the sensor is receiving the power it needs, which is exactly what we want.

Next, we'll verify that the TPS is also getting a proper Ground signal. Continue to: TEST 3: Making Sure The TPS Is Receiving Ground.

CASE 2: Voltage is missing or outside the 4.5 to 5 Volt range. If power isn't reaching the sensor, it won't be able to generate a varying signal voltage.

The most common causes of this issue include:

• A break or open-circuit in the wiring between the TPS connector and the engine computer's connector.
• Less common, a fault inside the engine control module (ECM) itself.

While diagnosing a missing 5 Volt reference is beyond the scope of this guide, you've now confirmed that the throttle position sensor itself is not to blame. Your next step is to track down and repair the issue that's preventing power from reaching the sensor.

TEST 3: Making Sure The TPS Is Receiving Ground

Up to this point, the results from your first two tests have shown the following:

• TEST 1: The TPS voltage signal doesn't change (increase or decrease) when the throttle plate is opened or closed.
• TEST 2: The TP sensor is receiving proper power.

In this third and final test, we'll verify whether the black with light blue stripe (BLK/LT BLU) is supplying Ground to the throttle position sensor.

According to the pinout of the connector above, Ground is delivered through terminal number 3 on the sensor's 3-wire connector.

This terminal should be connected to the BLK/LT BLU wire, which we'll test using our multimeter to see if it's delivering Ground.

NOTE: The sensor gets its Ground signal from the engine's fuel injection computer. Never apply 12 Volts directly to this wire —doing so will damage the computer. The voltage test outlined below is a safe way to check for Ground without the risk of any damage.

Let's get started:

1. 1

   Switch your multimeter to the Volts DC setting.

2. 2

   Attach the red multimeter lead to the positive (+) terminal of the battery.

3. 3

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

4. 4

   Disconnect the TP sensor from its wiring connector.

5. 5

   Use the black multimeter lead to carefully probe terminal 3 of the connector.
   
   Double-check that the BLK/LT BLU wire is connected to terminal number 3.
   
   NOTE: Be gentle when probing so you don't bend or damage the female terminal.

6. 6

   If Ground is present, your multimeter should display a voltage reading between 10 and 12 Volts DC.

Let's interpret your results:

CASE 1: You measured 10 to 12 Volts. This confirms that the sensor is receiving a good Ground signal.

If you've confirmed all three of the following conditions, then the TPS is defective and needs to be replaced:

• The TPS signal voltage doesn't change with throttle movement (from TEST 1).
• The sensor is getting the correct voltage (from TEST 2).
• Ground is present at terminal 3 (from this test).

CASE 2: No Ground detected. First, double-check your test connections and confirm that you're probing the correct terminal.

If the multimeter still doesn't show 10 to 12 Volts, the TPS itself is fine. The reason it isn't producing a changing voltage signal is because it's not receiving a proper Ground connection.

Although diagnosing a missing Ground goes beyond this tutorial, you now know the sensor itself isn't at fault. The issue lies elsewhere, and your next move is to find and fix the Ground supply problem.

The most common causes include:

• A break (open-circuit) in the wire running between the TPS connector and the fuel injection computer.
• In rare situations, a failure inside the computer itself could be responsible.

More 5.2L, 5.9L V8 Dodge Ram Van Tutorials

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