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:
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 B150 Van 3.9L: 1992, 1993, 1994.
- Ram B250 Van 3.9L: 1992, 1993, 1994.
- Ram B1500 Van 3.9L: 1995, 1996.
- Ram B2500 Van 3.9L: 1995, 1996.
- Ram D150 Pickup 3.9L: 1992, 1993.
- Ram D250 Pickup 3.9L: 1992, 1993.
- Ram 1500 Pickup 3.9L: 1994, 1995, 1996.
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 or van.
When it fails, and if your pickup or van is OBD I equipped (1994-1995), you'll see the check engine light lit by the following trouble code:
- Trouble Code 24: TPS Voltage Low.
- Trouble Code 24: TPS Voltage High.
On the 1996 OBD II equipped Dodge Ram pickup and van, you'll see the check engine light lit by one of the following trouble codes:
- 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 hesitates when you step on the accelerator pedal to move the vehicle.
- Lack of power as you accelerate the engine under load.
- Bad gas mileage.
To successfully diagnose the throttle position sensor, it's important to know that its job is to measure the amount the throttle plate (in the throttle body) opens and closes as you step on or step off the accelerator pedal.
Generally, the throttle position sensor generates a voltage signal of about 0.4 to 0.9 Volts DC when the throttle plate is closed (like when the engine is in idle and your foot is off the accelerator pedal).
The signal voltage increases as you step on the accelerator pedal and the throttle plate opens. When the throttle plate opens to its wide open throttle (WOT) position, it generates a voltage signal around 4.5 to 4.7 Volts DC.
So, in a nutshell, the key to finding out if the TPS is bad (or not) is to see if its producing an increasing/decreasing throttle angle voltage signal with a multimeter (and that's exactly what we'll do in this tutorial).
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 | BLK/LT BLU | Sensor Ground |
| 2 | ORG/DK BLU | Throttle Position Signal |
| 3 | VIO/WHT | 5 Volts |
Where To Buy The TPS And Save
The throttle positin sensor, for the 1992-1996 3.9L Dodge Ram pickup and van, 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.
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.
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.
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
Slowly close the throttle plate. The multimeter should show a decreasing voltage.
- 9
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.
