The throttle position sensor (TPS) on your 1991 TBI fuel-injected V8 Dodge Ram pickup is one of the easier sensors to check out.
The cool think is that you only need a multimeter —no scan tool. In this tutorial, I'll walk you through the process step by step.
With just three quick tests, you'll figure out fast if the TPS is working like it should or if its dead.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- Dodge Ram 150 Pickup 5.2L V8: 1991.
- Dodge Ram 250 Pickup 5.2L V8: 1991.
- Dodge Ram 150 Pickup 5.9L V8: 1991.
- Dodge Ram 250 Pickup 5.9L V8: 1991.
- Dodge Ram 350 Pickup 5.9L V8: 1991.
All TPS Sensor Test Tutorials:
- How To Test The TPS (1989-1990 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
If the TPS stops working, your engine's performance tanks. Here's what you're gonna run into:
- Trouble codes: The check engine light (CEL) will be triggered by:
- Code 24: TPS Voltage Is Too Low Or Too High.
- Engine won't start: In some cases, the engine is not gonna start.
- Hard to start: Gotta crank it several times before it finally catches.
- Hesitation: Stumbles when you take off or hit the gas while driving.
- No power: Step on it, and the engine just doesn't respond like it should.
- Bad gas mileage: The system kicks into 'limp-in' mode to protect the engine, but your fuel economy takes a serious hit.
How The TPS Works
You already know the accelerator pedal hooks up to the throttle plate through a mechanical cable. When the engine's running, here's how it works:
- Press the accelerator pedal and the throttle plate swings open, letting more air flow into the engine.
- Let off the pedal and the throttle plate shuts, cutting back the airflow.
Your Dodge Ram's fuel injection computer watches the throttle plate's angle using the throttle position sensor (TPS) every time you press or release the pedal.
If the TPS on your pickup is doing its job, here's how it should respond:
- Throttle closed: When the throttle plate's shut, the TPS puts out a low voltage (0.4 to 0.9 Volts DC).
- Throttle opening: As the plate starts to open, the voltage climbs steadily.
- Wide Open Throttle (WOT): At full throttle, the TPS usually pushes out around 4.5 Volts DC.
- Throttle closing: As the plate moves back to the closed spot, the voltage drops right back down to where it started.
If the TPS is faulty, that voltage signal won't go up or down when the throttle plate moves. It just stays stuck.
Where To Buy The TPS And Save
The following links will help you to comparison shop for the TPS for your 5.2L, 5.9L V8 Dodge Ram pickup. I think they'll save you a few bucks:
If you're unsure if this TPS is compatible with your specific 5.2L, 5.9L V8 Dodge Ram pickup, no worries. Once you visit the site, they'll check and ensure it's the right one by asking for more details about your vehicle. If it doesn't fit, they'll help find the correct one.
TEST 1: Testing The TPS Voltage Signal
For our first test, we're gonna tap into the TP sensor's signal wire and see if its producing a variable voltage signal.
The wire that carries the TP signal is the middle wire of the connector and it connects to terminal 2 (see illustration above).
NOTE: If you don't have a multimeter or need to upgrade yours, this is the one I use and recommend: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).
IMPORTANT: The TP sensor must remain connected to its electrical connector. You'll need to use a back probe on the connector or wiring piercing probe to access the signal in the wire. You can see an example of this tool here and where to buy it: Wire Piercing Probe.Alright, let's dive in:
- 1
Hook the black multimeter lead to the battery's negative (-) terminal.
- 2
Set your multimeter to DC Volts mode.
- 3
Turn the key to the ON position—but don't start the engine.
- 4
Touch the red multimeter lead to the middle wire on the TPS connector. Use a back probe or a wire-piercing tool.
NOTE: Keep the TPS plugged into its connector while testing. - 5
Your multimeter should show a voltage between 0.4 and 0.9 Volts DC with the throttle closed.
If you don't see that, no worries —keep going to the next steps. - 6
From the engine bay, slowly open the throttle by hand.
- 7
The voltage should rise.
At full throttle, you should see between 4 and 4.5 Volts DC on the meter. - 8
Slowly close the throttle back down.
- 9
The voltage should drop back to where it started.
- 10
While opening and closing the throttle plate, gently tap the TPS with a screwdriver handle.
A bad TPS will glitch or jump in voltage when tapped. A good one, the voltage signal won't budge —it stays smooth and steady.
Now, let's break down your test results:
CASE 1: The TPS voltage went up and down smoothly as you moved the throttle plate. That's the result you want. It means the TPS is working like it should.
This also tells you the TPS is getting both power and Ground from the fuel injection system.
CASE 2: The TPS voltage STAYED the same no matter how you moved the throttle. That usually means the sensor's bad.
To be sure, check that it's getting power and Ground. Head over to: TEST 2: Making Sure The TPS Is Receiving 5 Volts.
CASE 3: Your multimeter didn't pick up any voltage at all during the test. That's another sign the TPS is toast.
But before you swap it out, double-check it's getting both power and Ground. Go here: TEST 2: Making Sure The TPS Is Receiving 5 Volts.