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

You can check the condition of your throttle position sensor (TPS) —whether it's good or bad — using nothing more than a multimeter. No scan tool required. In this tutorial, I'll guide you through the testing process step by step.

With just three easy tests, you'll be able to quickly and confidently find out if your TPS is working as it should.

APPLIES TO: This tutorial applies to the following vehicles:

• Dodge Ram B150 Van 5.2L V8: 1991.
• Dodge Ram B250 Van 5.2L V8: 1991.
• Dodge Ram B250 Van 5.9L V8: 1991.
• Dodge Ram B350 Van 5.9L V8: 1991.

OTHER TPS SENSOR TESTS:

• How To Test The TPS (1989-1990 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The TPS (1992-1997 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The TPS (1997-2003 5.2L, 5.9L V8 Dodge Ram Van).

Symptoms Of A Bad Throttle Position Sensor

As you probably know, the accelerator pedal connects to the throttle plate using a mechanical cable. When the engine is running, here's what takes place:

• Pressing the accelerator pedal causes the throttle plate to open, letting more air flow into the engine.
• Releasing the pedal closes the throttle plate, which restricts the airflow going into the engine.

Your Dodge Ram van's fuel injection system monitors the angle of the throttle plate (based on how much the accelerator pedal is pressed or released) using the throttle position sensor, or TPS.

If the TPS stops working properly, you'll notice a sharp drop in engine performance. Here are some of the common signs of a failing throttle position sensor:

• Trouble codes: This diagnostic code will trigger the check engine light (CEL):
  • Code 24: TPS Voltage Too Low Or Too High.
• Engine won't start: No matter how long you crank it, the engine refuses to fire up.
• Difficult starts: The engine may take several attempts before it finally comes to life.
• Hesitation: You might feel a noticeable hesitation or a pause when accelerating from a stop or while driving. Feels like fuel got cut off for a few seconds.
• Power loss: The engine feels sluggish or unresponsive when you step on the gas.
• Poor fuel economy: The fuel injection system enters 'limp-in' mode to protect the engine, it reduces power and significantly affects your van's gas mileage.

Throttle Position Sensor Operation Basics

As I mentioned earlier, the throttle position sensor (TPS) creates a voltage signal that reflects the position of the throttle plate.

This is how a healthy TPS typically behaves:

• Throttle closed: When the throttle plate is fully shut, the TPS outputs a low voltage signal, usually around 0.3 to 0.9 Volts DC.
• Throttle opening: As you begin to open the throttle plate, the voltage sent by the TPS increases smoothly.
• Wide Open Throttle (WOT): At full throttle, the sensor usually reads around 4.5 Volts DC.
• Throttle closing: As the plate moves back to the closed position, the voltage drops steadily, returning to its initial low value.

If the TPS has failed, the voltage signal it sends will remain unchanged, regardless of the throttle plate movement.

Where To Buy The TPS And Save

The following links will help you to comparison shop for the TPS for your V8 Dodge Ram van. I think they'll save you a few bucks:

If you're unsure if this TPS is compatible with your specific V8 Dodge Ram van, no worries. Once you visit the site, they'll check and ensure it's the right one by asking for more details about your vehicle. If it doesn't fit, they'll help find the correct one.

TEST 1: Testing The TPS Voltage Signal

To kick off our TPS diagnostic, we'll start by checking the voltage signal the sensor puts out as we manually open and close the throttle plate from the engine bay (we won't be using the gas pedal to move the throttle).

To read the TPS output voltage, we'll hook up our multimeter to the center wire on the sensor's 3-wire connector.

NOTE: To check the TPS, you'll need a multimeter. If you don't own one, here's the model I personally use and recommend: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).

IMPORTANT: Keep the TP sensor connected to its electrical connector during testing. You'll need to back probe the connector or use a wire-piercing probe to tap into the signal wire. Here's a tool I suggest and where to get it: Wire Piercing Probe.

Let's begin:

1. 1

   Attach the black lead of your multimeter to the battery's negative (-) terminal.

2. 2

   Switch your multimeter to the DC Volts setting.

3. 3

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

4. 4

   Using a back probe or wire-piercing tool, connect the red multimeter lead to the middle wire of the TPS.
   
   NOTE: Do not disconnect the TPS from its electrical connector during this step.

5. 5

   At idle (throttle closed), your multimeter should show a voltage between 0.2 and 0.9 Volts DC.
   
   If it doesn't, don't worry just yet —proceed with the next steps.

6. 6

   Manually open the throttle from under the hood, slowly and steadily.

7. 7

   Watch for a smooth increase in voltage.
   
   At wide open throttle, your reading should fall somewhere around 4.5 Volts DC.

8. 8

   Gradually close the throttle plate again.

9. 9

   The voltage should steadily decrease, returning to its original low value.

10. 10

    Tap the TPS lightly using the handle of a screwdriver while opening and closing the throttle.
    
    If the TPS is damaged, tapping it may cause the voltage reading to glitch (jump or flicker). A properly functioning sensor will remain unaffected.

Let's review what your test results mean:

CASE 1: The TPS signal changed smoothly as you opened and closed the throttle plate. This result indicates the sensor is operating correctly.

It also confirms that the sensor is receiving both the required power and Ground connections from the fuel injection system.

CASE 2: The TPS signal stayed fixed at one voltage level, regardless of throttle movement. This often points to a faulty sensor.

To be certain, you'll want to verify that the TPS is receiving both power and Ground. We'll do that here: TEST 2: Making Sure The TPS Is Receiving 5 Volts.

CASE 3: The multimeter didn't register any voltage during testing. This usually suggests the TPS has failed.

However, before replacing it, confirm that it's actually getting the correct voltage and Ground signal. Go to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.