The throttle position sensor (TPS) on your Dodge Ram van can be easily checked without specialized or expensive diagnostic equipment.
In this tutorial, I'll walk you through three easy tests that'll help you diagnose the TPS using just a multimeter.
After completing these tests, your results will help you determine whether the sensor is faulty or operating correctly.
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 3.9L V6 Dodge Ram Van Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 3.9L V6 Dodge Ram 150 Van: 1989, 1990.
- 3.9L V6 Dodge Ram 250 Van: 1989, 1990.
Symptoms Of A Bad Throttle Position Sensor
The fuel injection computer constantly monitors the throttle position from the moment you turn the key to 'ON' position, as well as when the engine is operating.
If the TP sensor fails, the computer will display a TPS diagnostic trouble code (DTC) and trigger the check engine light to illuminate.
- Code 24: TPS Voltage Is Too Low.
- Code 24: TPS Voltage Is Too High.
Besides a TPS diagnostic trouble code, you may notice one or more of the following engine performance issues:
- Engine hesitation: You'll feel the van stutter or hesitate when you step on the gas to accelerate it from a stop or on the road.
- Loss of power: Your van just doesn't have the "umph" it used to have.
- Bad gas mileage: The fuel injection system switches to a "limp-in" mode, injecting extra fuel to protect the engine —you'll definitely have to fill up more often.
How The TPS Works
The TPS sensor's primary function is to track the movement of the throttle plate, as it opens or closes, when the gas pedal is pressed or released.
This throttle angle information is then transmitted as a variable DC voltage signal to the fuel injection computer.
Here's what a good TP sensor should show:
- Idle: Throttle Closed: The voltage reading should be within the range of 0.4 and 0.9 Volts DC.
- As You Hit the Pedal- Throttle Opening: The voltage reading should rise steadily, without any gaps.
- Wide Open Throttle (WOT): The voltage reading should peak at around 4.5 to 4.7 Volts DC.
- As You Let Off the Pedal- Throttle Closing: The voltage reading should decrease smoothly, without any gaps in the signal.
The main thing to remember about all of this is that a good TP sensor will generate a voltage signal that'll increase (or decrease) in a linear fashion with each pedal position change.
However, if the voltage remains stagnant and doesn't correspond to the pedal movement, there's a good chance that the throttle position sensor (TPS) is faulty (we still have to confirm that the sensor is receiving power and Ground).
To verify the TPS's functionality, we'll use a multimeter to measure its voltage output as the throttle plate (in the throttle body) transitions from idle to full wide open throttle (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:
The following links:
TEST 1: Checking The Throttle Position Sensor (TPS) Signal
Typically, when the throttle position sensor fails, it ceases to produce its variable voltage signal that corresponds to the throttle angle.
In other words, the TPS stops tracking and reporting the movement of the throttle plate's opening/closing, a condition that we can easily confirm using a multimeter.
IMPORTANT: The TPS must remain connected to its 3-wire connector during the TP signal voltage test. You can access the TPS signal by inserting a back-probe in the connector or using a wire-piercing probe to access the signal in the wire itself. You can see an example of this tool and where to buy it here: Wire Piercing Probe Tool.
Alright, these are the test steps:
- 1
Set your multimeter to measure DC voltage.
- 2
Connect the black multimeter test lead directly to the negative terminal of the battery.
- 3
Turn the ignition switch to ON, but do not crank or start the engine.
- 4
Connect the red multimeter test lead to the ORG/DK BLU wire of the TPS 3-wire connector.
The ORG/DK BLU wire is the one that connects to the male terminal 2 of the 3-wire TPS connector.
NOTE: Keep the TPS plugged into its connector while you test the TP signal. - 5
You should see a voltage between 0.3 and 1.0 Volts DC at this point with the throttle plate fully closed.
- 6
Open the throttle plate by hand.
You'll get the best results doing this right at the throttle body instead of pressing the gas pedal. - 7
Voltage should rise smoothly as the throttle plate opens.
With the throttle wide open, your multimeter should read somewhere between 3.2 and 4.9 Volts DC.
Again, do this by hand at the throttle body for the most accurate test result. - 8
Slowly close the throttle plate. The voltage should drop smoothly.
- 9
Tap the TPS gently with a screwdriver handle while opening and closing the throttle. Watch the multimeter.
This helps check for glitches in the voltage signal. A good TPS keeps a smooth signal even when tapped like this.
Now let's break down what your test results mean:
CASE 1: Voltage increased/decreased without any gaps. This is precisely what we're looking for. It indicates that the TP sensor on your Dodge Ram van is functioning properly.
Given that the ORG/DK BLU wire displays a clean and variable voltage signal, this also implies:
- The TPS is receiving the necessary 5V power supply.
- Additionally, it's also getting Ground.
No further testing is needed of the TP sensor.
CASE 2: No change in voltage. This typically indicates that the throttle position sensor may be faulty.
To confirm that the TPS is fried, we now need to make sure the TPS is receiving power and Ground. For the first of these two tests, go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.
CASE 3: The voltage reading glitched when the sensor was tapped. If the signal glitches while tapping the throttle position sensor with a screwdriver, it's clear indication that the TPS is bad and needs to be replaced.