How To Test The TPS (Dodge 3.9L, 5.2L, 5.9L)

The throttle position sensor can be easily tested using only a multimeter and in this article, I'll show you how.

This article covers troubleshooting diagnostic trouble codes (DTCs) P0121, P0122, P0123 on Dodge 3.9L, 5.2L and 5.9L pick ups, vans and SUVs.

NOTE: This tutorial only covers the throttle position sensor on late 1997 thru' 2003 Ram pickups/vans. For early 1997 thru' 1994 Ram pickups/vans, see the following tutorial:

  1. How To Test The Throttle Position Sensor (1994-1996 Dodge Ram Pickup).

The following wiring diagram article may come in handy:

  1. 1996-1998 TP Sensor Circuit Diagram (Dodge 3.9L, 5.2L, 5.9L).

En Español You can find this tutorial in Spanish here: Cómo Probar el Sensor TPS (Chrysler 3.9L, 5.2L, 5.9L) (at:

Symptoms Of A BAD TPS

You'll have the CHECK ENGINE LIGHT on your instrument cluster shining nice and bright for sure.

You'll also experience one or several of the following symptoms:

  1. TPS diagnostic trouble codes (DTC's).
    1. P0121: TPS Voltage Does Not Agree with MAP.
    2. P0122: Throttle Position Sensor Voltage Low.
    3. P0123: Throttle Position Sensor Voltage High.
  2. Really 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.
  3. 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.
  4. Engine may not start.

How The Throttle Position Sensor Works

How To Test The TPS (Dodge 3.9L, 5.2L, 5.9L)

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, 5.2L, 5.9L Dodge:

  1. The fuel injection computer supplies 5 Volts and ground to the throttle position sensor.
    1. 5 Volts is provided by the wire labeled with the number 3.
    2. Ground is provided by the wire labeled with the number 1.
  2. 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 .3 to .9 Volt. This value is what the PCM associates with a closed throttle.
    1. The TP signal is sent to the PCM by the wire labeled with the number 2.
  3. 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.
  4. 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, 5.2L, 5.9L Dodge running optimally.
  5. 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.