The throttle position sensor (TPS) can be very accurately tested with a multimeter to see if it's bad or not without removing it.
In this tutorial, I'll show you just how in a step-by-step manner. You'll also be able to diagnose the following throttle position sensor (TPS) diagnostic trouble codes: Code 24 (OBD-I) and P0121/P0122/P0123 (OBD-II).
Contents of this tutorial:
- Symptoms Of A Bad TPS.
- Basics Of The Throttle Position Sensor (TPS).
- Throttle Position Sensor Connector Pinout.
- Where To Buy The TPS And Save.
- TEST 1: Checking The Throttle Position Sensor (TPS) Signal.
- TEST 2: Making Sure The TPS Is Getting Power.
- TEST 3: Making Sure The TPS Is Getting Ground.
- More 5.2L, 5.9L V8 Dodge Ram Pickup Diagnostic Tutorials.
APPLIES TO: This tutorial applies to the following vehicles (since they use the exact same throttle position sensor):
- Dodge Ram 150 Pickup 5.2L, 5.9L: 1992, 1993.
- Dodge Ram 250 Pickup 5.2L, 5.9L: 1992, 1993.
- Doge Ram 350 Pickup 5.9L: 1992, 1993.
- Dodge Ram 1500 Pickup 5.2L, 5.9L: 1994, 1995, 1996.
- Dodge Ram 2500 Pickup 5.2L, 5.9L: 1994, 1995, 1996.
- Dodge Ram 3500 Pickup 5.9L: 1994, 1995, 1996.
3.9L V6 Dodge Ram Pickup TPS Tests:
3.9L V6 Dodge Ram Van TPS Tests:
5.2L, 5.9L V8 Dodge Ram Van TPS Tests:
Symptoms Of A Bad TPS
When the TP sensor fails in your V8 Dodge Ram pickup, you're gonna see one or more of the following symptoms:
- OBD-I diagnostic codes: On 1992–1995 models, this code will trigger the check engine light (CEL):
- Trouble Code 24: TPS Voltage Low.
- Trouble Code 24: TPS Voltage High.
- OBD-II diagnostic codes: On 19967 models, you might see one of these codes causing the CEL to light up:
- P0121: TPS Voltage Does Not Agree With MAP.
- P0122: Throttle Position Sensor Voltage Low.
- P0123: Throttle Position Sensor Voltage High.
- Engine refuses to start: No matter how long keep cranking the engine, it just won't fire up.
- Hard starting: You might have to crank the engine several times before it finally catches and runs.
- Stumbling on acceleration: When you press the accelerator, the engine may hesitate or stumble —especially noticeable when pulling away from a stop or trying to speed up.
- Loss of power: The engine feels weak or sluggish when you press the gas, and it doesn't respond like it should.
- Poor fuel economy: To protect the engine, the PCM may enter 'limp-in' mode, which causes it to inject more fuel than necessary —resulting in noticeably worse gas mileage.
Basics Of The Throttle Position Sensor (TPS)
Before we jump into testing, let's quickly go over what the throttle position sensor (TPS) does and how it behaves under normal conditions:
- Throttle plate controls airflow: The throttle plate controls how much air enters the engine as you press or release the accelerator pedal.
- TPS measures throttle angle: The TPS's job is to measure the angle of that throttle plate and convert it into a voltage signal.
- Throttle opening (you press the pedal): As the throttle plate opens, the TPS produces an increasing voltage signal.
- This signal is sent to the fuel injection computer (also called the PCM – Powertrain Control Module) through the middle wire of the TPS connector.
- Throttle closing (you let off the pedal): As the throttle plate angle decreases, the TPS responds by lowering the voltage signal sent to the PCM.
So, in a nutshell, the key to diagnosing the TPS is to verify —using a multimeter— that it's producing a smoothly increasing and decreasing voltage signal as the throttle plate moves. And that's exactly what we're going to do in this tutorial.
Throttle Position Sensor Connector Pinout
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
You can buy the throttle position sensor for your Dodge Ram pickup in just about any auto parts store but you'll spend a whole lot more because they mark it up quite a bit.
My suggestion is to buy it online or at least comparison shop to get an idea of how much it costs and how much you can save.
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.
Here are the test steps:
- 1
Place your multimeter in Volts DC mode and connect the red test lead to the ORG/DK BLU of the TP sensor harness connector (see image 1 of 2).
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). - 2
Ground the black multimeter test lead directly on the battery negative (-) post.
At this point (with the throttle plate closed) your multimeter should read a voltage between 0.3 to 1.0 Volts DC. - 3
Manually rotate the throttle.
You'll get the best results by opening and closing the throttle directly on the throttle body instead of stepping on the accelerator pedal. - 4
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. - 5
The multimeter should show a decreasing voltage as you begin to close the throttle.
- 6
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 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 Dodge Ram is bad and needs to be replaced.
Before replacing the TPS, I suggest that you verify that it's getting power and Ground. So, to continue with the TPS diagnostic, go to: TEST 2: Making Sure The TPS Is Getting Power.
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.
