The throttle position sensor, on the 1997-2001 3.9L V6 Dodge Ram pickup, is a simple 3-wire component that can easily be tested with a multimeter.
In this tutorial, I'll show you how to test it, and find out if it's bad, in 3 simple tests. You don't even have to remove it from its place to test it!
NOTE: You can find the 1992-1996 3.9L V6 Dodge Ram pickup throttle position sensor test here:
Contents of this tutorial:
- Symptoms Of A Bad TPS.
- How The Throttle Position Sensor Works.
- Where To Buy The TPS And Save.
- TEST 1: Testing The TPS Signal With A Multimeter.
- TEST 2: Making Sure The TPS Is Getting 5 Volts.
- TEST 3: Making Sure The TPS Is Getting Ground.
- TPS Code Won't Go Away.
- More 3.9L V6 Dodge Ram Pickup Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1997-2003 3.9L Dodge Ram Pickup y Van) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles (since they use the exact same throttle position sensor):
Full-size pickup:
- 3.9L V6 Dodge Ram 1500 Pickup: 1997, 1998, 1999, 2000, 2001.
- 3.9L V6 Dodge Ram 2500 Pickup: 1997, 1998, 1999, 2000, 2001.
3.9L V6 Dodge Ram Van TPS Tests:
5.2L, 5.9L V8 Dodge Ram Pickup TPS Tests:
Symptoms Of A Bad TPS
The throttle position sensor's job is to inform the fuel injection computer the throttle plate's angle as you step on or step off the accelerator pedal.
Since the TPS signal is monitored the entire time the engine is running, when it fails you'll have the check engine light on your instrument cluster shining nice and bright.
You'll also see one or several of the following symptoms:
- TPS diagnostic trouble codes (DTCs): Check engine light will be on and you'll see one of these codes:
- P0121: TPS Voltage Does Not Agree with MAP.
- P0122: Throttle Position Sensor Voltage Low.
- P0123: Throttle Position Sensor Voltage High.
- Poor fuel economy: You're filling up more often, and it's not just because gas prices are high—your pickup is clearly burning more fuel than it used to.
- Lack of power: When you press the accelerator, the engine feels sluggish. It's missing that "kick" it once had.
- Hesitation when accelerating: As you try to take off, the engine stumbles for a moment —almost like the power briefly cuts out before catching up.
- Cranks but won't start: The engine turns over, but it just won't fire up and run.
How The Throttle Position Sensor Works
The throttle position sensor (TPS) monitors the angle of the throttle plate. Here's a simplified breakdown of how it functions when you start up your 3.9L V6 Dodge Ram pickup:
- Sensor powered on: The fuel injection computer (PCM) sends both 5 Volts and Ground to the TPS.
- The 5-Volt supply comes through the wire labeled number 3.
- Ground is provided via the wire labeled number 1.
- Throttle at idle: When the throttle is closed and the sensor is powered, the TPS sends a low voltage signal —around 0.3 to 0.9 Volts DC— to the PCM. This tells the computer the throttle is in the closed position.
- The voltage signal travels through the wire labeled number 2.
- Throttle opens during acceleration: As you put the truck in gear and press the accelerator, the throttle plate opens:
- The TPS detects this movement and responds by sending an increasing voltage signal to the PCM.
- This rising voltage tells the computer it's time to adjust fuel delivery, ignition timing, and other critical functions to keep the engine running efficiently.
- At Wide Open Throttle (WOT): When the throttle is fully open, the TPS typically outputs close to 4.5 Volts DC.
- Throttle returns to idle: As you release the gas pedal to slow down, the throttle plate closes again. The TPS drops the voltage back to its base reading, and the process repeats as needed.
Pretty straightforward, right? The great thing is that testing the TPS is just as simple. All you're doing is confirming that the sensor produces a changing voltage signal as the throttle plate moves —something you can easily check with a multimeter set to Volts DC.
If you're not getting a voltage signal from the TPS, the next logical step is to verify that it's receiving proper power and Ground from the PCM. Both of these checks can be done with your multimeter as well.
Where To Buy The TPS And Save
The throttle position sensor, on the 1997-2001 3.9L V6 Dodge Ram pickup, is a very common and inexpensive component. The following links will help you to comparison shop and save a few bucks on its purchase.
Not sure if the above throttle position sensor (TPS) fits your particular 3.9 V6 Dodge Ram pickup? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Testing The TPS Signal With A Multimeter
The get this show on the road, we're gonna' check that the TPS voltage signal increases/decreases as we open/close the throttle plate.
Generally, when the TP sensor fails, its TPS voltage signal will stay stuck in one voltage value as you open/close the throttle plate.
The wire, that we're gonna' connect the multimeter to, is the orange with dark blue stripe (ORG/DK BLU) wire. In the photo above, I've labeled this wire with the number 2.
NOTE: One last thing: it's best to test the throttle position sensor (TPS) with the engine warmed up. This will increase the accuracy of your test result, especially if the TP sensor is failing intermittently.
OK, let's start:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the black multimeter test lead directly on the battery negative (-) post
- 3
Turn the key to the ON position but don't crank or start the engine.
- 4
Connect the red multimeter test lead to the ORG/DK BLU wire of the TP sensor harness connector (see image above).
NOTE: The TP sensor connector needs to be connected to the TPS, so you'll need to either back-probe the connector or use a wire piercing probe to get to the signal inside the wire (to see what a wire piercing probe looks like: Wire Piercing Probe Tool). - 5
Your multimeter should read a voltage between 0.3 to 1.0 Volts DC with the throttle plate closed.
- 6
Manually rotate the throttle plate.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 7
The multimeter should show an increasing voltage as you (or your helper) open up the throttle.
With the throttle plate completely open, your multimeter should read: 3.2 to 4.9 Volts DC.
You'll get the best results by opening and closing the throttle directly on the throttle body instead of stepping on the accelerator pedal. - 8
Begin closing the throttle plate slowly.
- 9
The multimeter should show a decreasing voltage as you begin to close the throttle.
- 10
Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle and observer the multimeter.
The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gap's in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screw-driver's handle.
Let's examine your test results:
CASE 1: The TPS voltage signal increased/decreased as you open/closed the throttle plate. This is the correct test result and confirms that the throttle position sensor is working correctly.
Now, if the throttle position sensor code won't go away, consult this section: TPS Code Won't Go Away for a few more suggestions as to what could be causing the TPS diagnostic trouble code (DTC).
CASE 2: The TPS voltage signal DID NOT increase/decrease as you open/closed the throttle plate. This test result generally tells you that the TPS is bad and needs to be replaced.
But to be sure that the TPS is bad, you need to make sure that it's getting 5 Volts and Ground. For the first of these two tests, go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.
CASE 3: The TPS voltage signal had gaps in its reading as you tapped the TPS with the screwdriver. This test result tells you that the TPS is bad and needs to be replaced.
