The throttle position sensor, on the 1997-2003 3.9L V6 Dodge Ram 1500 Pickup/Van, 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/van throttle position sensor test here:
Contents of this tutorial:
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):
- Dodge Ram 1500 Pickup 3.9L: 1997, 1998, 1999, 2000, 2001.
- Dodge Ram Van B1500 Van 3.9L: 1997, 1998.
- Dodge Ram Van 1500 Van 3.9L: 1999, 2000, 2001, 2002, 2003.
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 (DTC's).
- P0121: TPS Voltage Does Not Agree with MAP.
- P0122: Throttle Position Sensor Voltage Low.
- P0123: Throttle Position Sensor Voltage High.
- Bad gas mileage. You know that it's not the price of gasoline that has you thinking that your pick up or SUV is costing you more at the pump.
- No power and/or hesitation as you accelerate the vehicle. It feels like all of a sudden someone cut the power out momentarily as you step on the gas to get the vehicle moving.
- Engine may not start.
How The Throttle Position Sensor Works
The throttle position sensor's job is to measure the angle of the throttle. So here, in a nutshell, is how the throttle position sensor works when you crank and start your 3.9L V6 Dodge Ram 1500 Pickup/Van:
- The fuel injection computer supplies 5 Volts and Ground to the throttle position sensor.
- 5 Volts is provided by the wire labeled with the number 3.
- Ground is provided by the wire labeled with the number 1.
- Now, since the throttle is closed, the TPS (with power and Ground supplied) sends the PCM (Powertrain Control Module=Fuel Injection Computer) a DC voltage signal of about 0.3 to 0.9 Volt. This value is what the PCM associates with a closed throttle.
- The TP signal is sent to the PCM by the wire labeled with the number 2.
- Once you throw your Dodge vehicle in drive and accelerate the car, the throttle opens and the throttle position sensor immediately sends this change of the throttle angle as an INCREASING voltage signal to the PCM.
- With this increasing voltage signal, the PCM knows its time to inject more fuel, advance ignition timing, and a host of other things it has to do to keep your 3.9L Dodge running optimally.
- As you let go off the accelerator pedal to slow down, the throttle plate closes and of course the TP sensor sends the info to the PCM as it returns to its base voltage signal, till the whole cycle begins again.
Pretty easy stuff? The cool thing is that the tests to check out the TP sensor's performance are as easy too. Since testing the TPS simply involves making sure that the sensor is creating a throttle angle voltage signal (which can be verified with a multimeter in Volts DC mode).
If the TP sensor is not creating a voltage signal, then the next steps are to make sure that it's getting power and Ground from the PCM. These two things you can also verify with your multimeter.
IMPORTANT: Since you'll be working in the engine compartment take all necessary safety precautions and use common sense.
Where To Buy The TPS And Save
The throttle position sensor, on the 1997-2003 3.9L V6 Dodge Ram Pickup/Van, 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 1500 Pickup or Van? 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:
Place your multimeter in Volts DC mode.
Connect the black multimeter test lead directly on the battery negative (-) post
Turn the key to the ON position but don't crank or start the engine.
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).
Your multimeter should read a voltage between 0.3 to 1.0 volt DC with the throttle plate closed.
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.
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.
Begin closing the throttle plate slowly.
The multimeter should show a decreasing voltage as you begin to close the throttle.
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 Will Not 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.