P0121 TPS Code Explained (2002-2007 4.7L V8 Dodge Ram Pickup)

  • By: Abraham Torres-Arredondo
  • Created: 01 July 2025
  • Updated: 01 July 2025
  • Articl Id: 839
P0121 TPS Code Explained (2002, 2003, 2004, 2005, 2006, 2007 4.7L V8 Dodge Ram Pickup)

Code P0121 is a common throttle position sensor (TPS) trouble code for the 2002–2007 4.7L V8 Dodge Ram pickup. It means the PCM is seeing a TPS voltage that doesn't match the expected values for the current engine operating conditions.

This usually points to a worn-out TPS sensor, a wiring problem, or a glitchy signal that throws the computer off.

In this tutorial, I'll walk you through what this code really means (including the info that professional techs use and rely on), what causes it, and whether you should test the TPS before replacing it —or go ahead and swap it out.

Whether you're a DIYer or a pro tech, this guide has got you covered!

Contents of this tutorial:

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.7L V8 Dodge Ram 1500 Pickup: 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.

TPS MULTIMETER TESTS:

TPS WIRING DIAGRAMS:

OTHER TPS TROUBLE CODES EXPLAINED:

What Does P0121 Really Mean?

Depending on the type of scan tool you're using, this DTC may show up with either a generic OBD II definition or a factory-specific one:

  • Generic Definition:
    • P0121: Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem.
  • Factory Definition:
    • P0121: TPS Voltage Does Not Agree With MAP.

To successfully diagnose a P0121, it's important to understand how the system works on your 2002–2007 4.7L V8 Dodge Ram pickup. The TPS sends a voltage signal that increases as you press the gas pedal and decreases as you let off. The PCM knows how fast that voltage should rise or fall as the throttle opens and closes.

At the same time, the PCM compares the TPS signal to the MAP sensor's input. These two signals should reflect engine load conditions: when manifold vacuum is high —like at idle with your foot off the gas pedal— TPS voltage should be low. When vacuum drops —like when you're stepping on the gas under load— TPS voltage should rise.

If that correlation doesn't make sense for more than 4 seconds —for example, if the TPS voltage jumps too fast, drops out, or stays stuck while the MAP sensor shows changing engine load— the PCM sets a P0121 TPS Voltage Does Not Agree With MAP trouble code.

In simple terms: the computer no longer trusts what the TPS is telling it. A P0121 means the TPS signal doesn't match what the PCM expects to see under current engine operating conditions.

This mismatch can confuse the PCM and trigger all sorts of driveability issues —let's take a look at the most common symptoms you might experience when this code shows up.

Common Symptoms Of A Code P0121

If your 4.7L Dodge Ram has a P0121 code, you'll usually feel it while driving. Sometimes the check engine light is the only clue, but most of the time, you'll notice one or more of the following:

  • Rough or unstable idle.
  • Engine hesitation when accelerating.
  • Unpredictable or delayed throttle response.
  • Transmission shifting issues (hard shifts or delays).
  • Reduced engine power or limp mode.

These symptoms come and go depending on how the TPS is failing —sometimes it only acts up when hot, or when you hit a bump in the road.

Now that you've seen what this code feels like behind the wheel, let's dig into the most common reasons it shows up in the first place.

What Causes Code P0121?

Code P0121 can be triggered by several different issues, but they all have one thing in common: the TPS signal doesn't match what the PCM expects. Here are the most common causes on the 2002–2007 4.7L V8 Dodge Ram pickup:

  • A worn-out or failing TPS sensor.
  • A loose TPS connector or damaged wiring.
  • Corrosion inside the TPS connector terminals.
  • A fault in the 5 Volt supply circuit.
  • A problem with its Ground circuit.
  • A faulty MAP sensor.
  • A failed sensor on the same 5 Volt or Ground circuit that's shorted internally and causing interference
    • Several other sensors share the same 5 Volt and Ground circuits as the TPS
  • Faulty PCM (rare, but possible).

Yes, the TPS itself could be bad —but in my experience, many P0121 issues come down to a wiring or power/Ground problem that's interfering with the signal the TPS is trying to send to the PCM.

The best way to figure out what's really going on is to test the TPS sensor with a multimeter and confirm that it's producing the correct signal output —and that it's receiving both 5 Volts and a solid Ground.

So what's the next step —replace the sensor or test it first? Let's take a closer look at both options.

Should You Replace The TPS?

If your Dodge Ram pickup has a P0121 code, replacing the TPS sensor might seem like the quickest solution —and in many cases, it works. The sensor isn't very expensive, and it's easy to remove and install, so a lot of folks simply replace it without testing it first.

And honestly, if the TPS really is the problem, replacing right off the bat will get your pickup back on the road with no more check engine light.

So if you're going that route, here are two options I recommend. These links go to brands I trust, and using them helps support the site —at no extra cost to you:

Now, if you'd rather confirm the issue before buying a part —especially since the TPS is so easy to access and test— you absolutely can. It's a smart move, especially if the real problem is something like a wiring fault, corroded connector, or a missing 5 Volt reference or Ground.

Here's the step-by-step tutorial that'll walk you through checking the TPS signal, the 5 Volt reference, and the Ground circuit with just a multimeter:

More 4.7L V8 Dodge Ram Pickup Diagnostic Tutorials

I've written quite a few tutorials for the 4.7L V8 Dodge Ram pickup. You can find them in this index:

Here's a small sample of the tutorials you'll find in the index:

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