The throttle position sensor is probably one of the easiest fuel injection system components to test and you don't need any expensive test equipment to do it.
In this tutorial I'm gonna' show you how to test the TPS in 3 tests. These 3 tests are done with a multimeter.
With your test results you'll be able to easily find out if the TPS is bad or not.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- Throttle Position Sensor Operation Basics.
- 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 Pickup Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1992-1996 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):
- Ram 150 Pickup 3.9L V6: 1992, 1993.
- Ram 250 Pickup 3.9L V6: 1992, 1993.
- Ram 1500 Pickup 3.9L V6: 1994, 1995, 1996.
3.9L V6 Dodge Ram Van TPS Tests:
5.2L, 5.9L V8 Dodge Ram Pickup TPS Tests:
Symptoms Of A Bad Throttle Position Sensor
The throttle position is constantly monitored by the fuel injection computer of your 3.9L V6 equipped Dodge Ram pickup.
When it fails, you'll see the check engine light lit by the following trouble code:
- OBD I equipped (1994-1995):
- Trouble Code 24: TPS Voltage Low.
- Trouble Code 24: TPS Voltage High.
- 1996 OBD II equipped Dodge Ram pickup:
- P0121: TPS Voltage Does Not Agree with MAP.
- P0122: Throttle Position Sensor Voltage Low.
- P0123: Throttle Position Sensor Voltage High.
You're also gonna' see one or more of the following symptoms:
- Engine hesitation: When you step on the accelerator pedal to move the vehicle, feels like power got cut off for a split second and then gets turned back on.
- Lack of power: As you step on the gas and you accelerate the engine (from a stop or from cruising speed), it just doesn't have the power like it used to.
- Bad gas mileage: The fuel injection computer is gonna dump more fuel into the engine and you miles per gallon is gonna go out the window.
- Limp-in mode activated: The fuel injection computer goes into limp-in mode and engine power is reduced.
Throttle Position Sensor Operation Basics
To properly diagnose the throttle position sensor (TPS), it helps to understand its basic role: the TPS tracks how much the throttle plate inside the throttle body opens or closes as you press or release the accelerator pedal.
Here's a simplified breakdown of how it works:
- Sensor receives power: The fuel injection computer (PCM) supplies the TPS with both 5 Volts and a Ground connection.
- 5 Volts are delivered through the wire labeled terminal 1.
- Ground is provided through the wire labeled terminal 3.
- Throttle fully closed (engine at idle): With the throttle shut and your foot off the gas pedal, the TPS sends out a low voltage signal —typically between 0.4 and 0.9 Volts DC.
- Throttle begins to open: As you press the accelerator and the throttle plate starts to move, the voltage signal from the TPS begins to rise.
- Wide Open Throttle (WOT): At full throttle, the sensor typically sends a voltage signal in the range of 4.5 to 4.7 Volts DC.
- Throttle closing again: When you ease off the accelerator, the throttle plate returns to its closed position, and the voltage drops back to its base level. This cycle continues as you drive.
In short, diagnosing a TPS comes down to one simple question: Is the sensor producing a steadily rising and falling voltage signal as the throttle plate moves? I'll walk through how to test that with a multimeter in this tutorial.
Throttle Position Sensor Circuit Descriptions
In the table below, you'll find a short description of what each wire does:
| 1992-1996 Dodge Ram TPS Circuits | ||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | VIO/WHT | 5 Volts |
| 2 | ORG/DK BLU | Throttle Position Signal |
| 3 | BLK/LT BLU | Sensor Ground |
Where To Buy The TPS And Save
The throttle position sensor, for the 1992-1996 3.9L Dodge Ram pickup, is not an expensive component. The following links will help you comparison shop and hopefully save you a few bucks on its purchase:
The following links:
TEST 1: Checking The Throttle Position Sensor (TPS) Signal
The most common throttle position sensor (TPS) failure is a sensor that just stops creating a varying throttle angle voltage signal.
In other words, it stops measuring/reporting the throttle angle of the throttle plate. You and I can very easily check this with a multimeter and that's what we'll do in this test section.
Need to buy a multimeter or an upgrade? This is the one I have and use: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).
IMPORTANT: The throttle position sensor must remain connected to its harness connector to accomplish this test. You'll need to either back-probe the connector (with a back probe) or use a wire piercing probe to get to the signal inside the wire. You can see an example of this tool and where to buy it here: Wire Piercing Probe Tool.
Here are the test steps:
- 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 connector.
NOTE: The TP sensor needs to remain connected its electrical connector to test its signal. - 5
Your multimeter should read a voltage between 0.3 to 1.0 Volts DC at this point (with the throttle plate closed) .
- 6
Manually rotate the throttle plate.
NOTE: You'll get the best results by opening and closing the throttle 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 plate.
With the throttle plate completely open, your multimeter should read: 3.2 to 4.9 Volts DC. - 8
Slowly close the throttle plate.
- 9
The multimeter should show a decreasing voltage.
- 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 take a look at what your test results mean:
CASE 1: The voltage increased and decreased smoothly and without gaps. This is the correct and expected test result and it tells that the throttle position sensor on your Dodge Ram IS NOT defective.
Since the throttle position sensor is creating an increasing/decreasing voltage signal on the ORG/DK BLU wire, this test result also says that:
- The TPS is getting power on the VIO/WHT wire of its harness connector.
- The TPS is getting Ground on the BLK/LT BLU wire of its harness connector.
CASE 2: The voltage DID NOT increase or decrease. This test result usually means that the throttle position sensor on your 3.9L Dodge Ram is bad.
Before replacing the TPS, it's important to check that it's getting power and Ground. For the next test, go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.
CASE 3: The TP sensor signal's voltage showed gaps in its voltage output as you tapped the sensor with the screwdriver. If the gaps in the multimeter's voltage readings only showed up when you were tapping on the TPS (with the screwdriver's handle) then this test result tells you that the TPS is bad and needs to be replaced.
