You don't need any special or costly diagnostic tools to test the throttle position sensor (TPS) on your V8 Dodge Ram van.
In this step-by-step tutorial, I'll show you how to perform three simple tests using nothing more than a basic multimeter.
After completing these tests, your results will make it clear whether your TPS is functioning properly or needs to be replaced.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- How The TPS Works.
- Throttle Position Sensor Circuit Descriptions.
- Where To Buy The TPS And Save.
- TEST 1: Checking The Throttle Position Sensor (TPS) Signal.
- TEST 2: Making Sure The TPS Is Getting 5 Volts.
- TEST 3: Making Sure The TPS Is Getting Ground.
- More 5.2L, 5.9L V8 Dodge Ram Van Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- Dodge Ram B150 Van 5.2L V8: 1989, 1990.
- Dodge Ram B250 Van 5.2L V8: 1989, 1990.
- Dodge Ram B250 Van 5.9L V8: 1989, 1990.
- Dodge Ram B350 Van 5.9L V8: 1989, 1990.
Symptoms Of A Bad Throttle Position Sensor
From the moment you turn the key to the 'ON' position and throughout engine operation, the fuel injection computer keeps a constant eye on the throttle position.
When the TPS malfunctions, the computer will register a diagnostic trouble code (DTC) related to the sensor and activate the check engine light on your dashboard.
- Code 24: TPS voltage reading is below the expected range.
- Code 24: TPS voltage reading is above the acceptable limit.
In addition to setting a TPS-related trouble code, you might also run into one or more of the following drivability symptoms:
- Engine hesitation: The van may stumble or hesitate when you press the gas pedal to accelerate —whether you're taking off from a stop or already cruising.
- Loss of power: It feels like your van just doesn't have the strength or responsiveness it once did.
- Poor fuel economy: The engine management system switches into "limp-in" mode, over-fueling the engine to avoid damage —and this means you'll be visiting the gas station more often.
How The TPS Works
The main job of the throttle position sensor (TPS) is to monitor how the throttle plate moves (whether it's opening or closing) in response to the gas pedal being pressed or released.
This movement is converted into a variable DC voltage signal, which is sent to the fuel injection computer to help it manage engine performance.
Here's what you should see from a TPS that's working correctly:
- Idle → Throttle Fully Closed: The voltage should fall between 0.4 and 0.9 Volts DC.
- Accelerating → Throttle Opening: The voltage should rise steadily and smoothly, with no sudden drops or flat spots.
- Wide Open Throttle (WOT): You should get a peak reading in the neighborhood of 4.5 to 4.7 Volts DC.
- Releasing the Pedal → Throttle Closing: The voltage should steadily drop back down, again without any interruptions in the signal.
The key takeaway here is that a healthy TPS produces a voltage signal that changes smoothly and consistently as the throttle position changes.
If the voltage doesn't shift in sync with the pedal —staying flat or jumping unpredictably— then there's a strong possibility the TPS is faulty (though we'll still need to confirm that it's getting proper power and Ground).
To check the TPS, we'll use a multimeter to track its voltage output while the throttle plate moves from a fully closed position to fully open (WOT).
Throttle Position Sensor Circuit Descriptions
In the table below, you'll find a short description of what each of the 3 wires coming out of the 3-wire does:
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Violet with white stripe (VIO/WHT) or Violet (VIO) | 5 Volts |
| 2 | Orange with dark blue stripe (ORG/DK BLU) | Throttle Position Signal |
| 3 | Black with light blue stripe (BLK/LT BLU) | Sensor Ground |
Where To Buy The TPS And Save
The throttle position sensor for your Dodge Ram van is pretty affordable. Check out the following links and comparison shop for a known automotive brand TP sensor:
TEST 1: Checking The Throttle Position Sensor (TPS) Signal
When the throttle position sensor fails, it generally stops producing the changing voltage signal that reflects the throttle angle position.
In simple terms, the TPS no longer tracks or reports the throttle plate's open/close movement —something we can easily test using a standard multimeter.
IMPORTANT: The TPS must stay connected to its 3-wire harness during the voltage test. To access the TP signal, you'll either need to back-probe the connector or use a wire-piercing probe to tap into the signal wire directly. You can view an example of this tool and where to get one here: Wire Piercing Probe Tool.
Alright, here's how to run the test:
- 1
Set your multimeter to read DC voltage.
- 2
Attach the black multimeter lead to the battery's negative terminal.
- 3
Switch the ignition key to the ON position, but don't start or crank the engine.
- 4
Place the red multimeter lead on the ORG/DK BLU wire of the TPS connector.
This ORG/DK BLU wire connects to terminal 2 of the sensor's 3-wire connector.
NOTE: Leave the TPS connected to its 3-wire connector while performing this test. - 5
You should see a voltage between 0.4 and 0.9 Volts DC when the throttle plate is fully closed (idle position).
- 6
Manually open the throttle plate.
You'll get the most accurate reading if you move the plate by hand at the throttle body rather than using the gas pedal. - 7
The voltage should increase steadily as the throttle opens wider.
With the throttle fully open, expect a reading between 4.5 and 4.7 Volts DC.
Again, move it by hand for best result. - 8
Slowly let the throttle close. Watch for a smooth voltage decrease.
- 9
Lightly tap the TPS with the handle of a screwdriver while opening and closing the throttle. Observe the multimeter.
This helps detect any signal interruptions (glitches). A healthy TPS will continue producing a stable, uninterrupted signal, even when lightly tapped.
Now let's look at what your test results mean:
CASE 1: Voltage rises and falls smoothly, with no gaps. That's exactly what you want to see. It means the TPS on your Dodge Ram van is operating correctly.
Because the ORG/DK BLU wire shows a consistent and responsive voltage signal, this also confirms:
- The TPS is receiving its 5V reference voltage.
- It's also getting a proper Ground connection.
No further TPS testing is necessary.
CASE 2: Voltage stays flat and doesn't change. This usually indicates the TPS isn't working as it should.
To be sure it's a failed sensor, we'll need to check whether it's getting both power and Ground. For the first check, go here: TEST 2: Making Sure The TPS Is Getting 5 Volts.
CASE 3: Voltage signal glitches when tapping the sensor. If the voltage jumps or cuts out while gently tapping the TPS, that's a clear sign the sensor is faulty and should be replaced.