You don't need a scan tool to check the throttle position sensor (TPS) on your V8 Dodge Ram pickup with throttle body fuel injection (TBI).
In this tutorial, I'm gonna show you how to check it with three simple tests and you only need a multimeter.
With the results of these three tests, you'll know for sure if the sensor's working right or if it's shot.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- How The TPS Works.
- 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 5.2L, 5.9L V8 Dodge Ram Pickup Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- Dodge Ram 100 Pickup 5.2L V8: 1989.
- Dodge Ram 150 Pickup 5.2L V8: 1989, 1990.
- Dodge Ram 250 Pickup 5.2L V8: 1989, 1990.
- Dodge Ram 150 Pickup 5.9L V8: 1989, 1990.
- Dodge Ram 250 Pickup 5.9L V8: 1989, 1990.
- Dodge Ram 350 Pickup 5.9L V8: 1989, 1990.
All V8 Dodge Ram Pickup TPS Sensor Test Tutorials:
- How To Test The TPS (1991 5.2L, 5.9L V8 Dodge Ram Pickup).
- How To Test The TPS (1992-1996 5.2L, 5.9L V8 Dodge Ram Pickup).
- How To Test The TPS (1997-2003 5.2L, 5.9L V8 Dodge Ram Pickup).
Symptoms Of A Bad Throttle Position Sensor
From the moment you turn the key to the 'ON' position —and while the engine's running —the fuel injection computer keeps an eye on the throttle position nonstop.
When the TPS goes bad, the computer throws a diagnostic trouble code (DTC) and flips on the check engine light:
- Code 24: TPS Voltage Is Too Low Or Too High.
Besides seeing that code, you'll probably notice one or more of the following engine performance problems:
- Engine hesitation: The truck stutters when you hit the gas —either from a stop or when you're cruising and press down for more speed.
- Loss of power: It just doesn't pull like it used to.
- Bad gas mileage: The computer kicks in "limp-in" mode, dumping in extra fuel to keep the engine safe. This ends up making you fill up more often.
How The TPS Works
The throttle position sensor tracks how much the throttle plate moves when you press or release the gas pedal.
It sends this throttle angle info as a changing DC voltage signal to your Dodge Ram pickup's fuel injection computer.
Here's what you should see if the TPS is working right:
- Idle (throttle closed): Voltage should sit somewhere between 0.4 and 0.9 Volts DC.
- When you press the pedal (throttle opening): Voltage should rise smoothly —no skips or dead spots.
- Wide open throttle (WOT): You should get around 4.5 to 4.7 Volts DC at full throttle.
- When you let off (throttle closing): Voltage should drop back down steadily, again with no gaps in the signal.
The key thing here is this: a good TPS gives you a smooth, steady voltage increase or decrease every time the pedal moves.
If the voltage stays flat or doesn't match the pedal movement, the TPS is bad (we'll still need to make sure it's getting power and Ground first, though).
To check if it's working like it should, we're gonna use a multimeter and watch the voltage change as the throttle plate moves from its closed position all the way to wide open throttle (WOT).
Throttle Position Sensor Circuit Descriptions
Here's a brief description of what each of the 3 wires coming out of the 3-wire connector does:
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Violet with white stripe (VIO/WHT) or Violet (VIO) | 5 Volts |
| 2 | Orange with dark blue stripe (ORG/DK BLU) | Throttle Position Signal |
| 3 | Black with light blue stripe (BLK/LT BLU) | Sensor Ground |
Where To Buy The TPS And Save
The throttle position sensor for your Dodge Ram pickup isn't that expensive. Check out the following links and comparison shop for a known automotive brand TP sensor:
The following links:
TEST 1: Checking The Throttle Position Sensor (TPS) Signal
Usually, when the throttle position sensor fails, it stops sending out the variable voltage signal that matches the throttle angle.
Basically, the TPS quits tracking and reporting the movement of the throttle plate, something you and I can easily check with a multimeter.
IMPORTANT: The TPS to stay connected to its 3-wire connector during this test. You can access the TPS signal by either back-probing the connector or using a wire-piercing probe to get into the wire itself. You can see an example of the tool and where to buy it here: Wire Piercing Probe Tool.
Here's what you need to do:
- 1
Set your multimeter to measure DC voltage.
- 2
Connect the black multimeter lead to the negative terminal of the battery.
- 3
Turn the ignition to the ON position, but don't start the engine.
- 4
Attach the red multimeter lead to the ORG/DK BLU wire on the TPS 3-wire connector.
The ORG/DK BLU wire connects to male terminal 2 on the TPS connector.
NOTE: Keep the TPS connected to its 3-wire connector during the test. - 5
Check for a voltage between 0.4 and 0.9 Volts DC with the throttle plate fully closed.
- 6
Manually open the throttle plate.
NOTE: For the best results, do this right at the throttle body, not by pressing the gas pedal. - 7
The voltage should rise steadily as the throttle plate opens.
When the throttle is wide open, you should see a reading between 4.5 and 4.7 Volts DC.
Again, do this by hand at the throttle body for the most accurate results. - 8
Slowly close the throttle plate and watch the voltage drop smoothly.
- 9
Tap the TPS gently with a screwdriver handle while opening and closing the throttle. Keep an eye on the multimeter.
This helps you check for any glitches in the voltage. A good TPS will show a smooth signal, even when tapped.
Now, let's go over what the test results mean:
CASE 1: The voltage changes smoothly without any gaps/glitches. This is exactly what we want to see. It means the TPS on your V8 Dodge Ram pickup is working properly.
If the ORG/DK BLU wire is showing a clean, variable voltage, it also means:
- The TPS is getting the required 5V power supply.
- And, it's getting Ground too.
No further testing of the TPS is necessary.
CASE 2: No voltage change. This usually means the TPS is faulty.
To make sure the TPS is really bad, we'll check if it's getting power and Ground. For the first test, go here: TEST 2: Making Sure the TPS Is Getting 5 Volts.
CASE 3: The voltage glitched when the sensor was tapped. If tapping the sensor causes the voltage to glitch, that's a clear sign the TPS is bad and needs replacing.