Testing the throttle position sensor (TPS) on the 4.6L and 5.4L Ford E-Series vans isn't difficult. In fact, you don't need any expensive diagnostic tools to do it.
In this tutorial, I'll explain how to test it with three tests using a multimeter. By the end of these tests, your results will let you know if the throttle position sensor is OK or if it has failed. You'll also be able to diagnose the following trouble codes: P0121, P0122, and P0123.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- Throttle Position Sensor Circuit Descriptions.
- How Does The Throttle Position Sensor Work?
- Where To Buy The Throttle Position Sensor And Save.
- TEST 1: Testing The TPS Signal.
- TEST 2: Making Sure The TPS Is Getting 5 Volts.
- TEST 3: Making Sure The TPS Is Getting Ground.
- TPS Code Won't Go Away.
APPLIES TO: Applies to the following gasoline powered vehicles:
- 4.6L, 5.4L Ford E150: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.6L, 5.4L Ford E250: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 5.4L Ford E350: 1997, 1998, 1999, 2000, 2001, 2002, 2003.
Symptoms Of A Bad Throttle Position Sensor
The throttle position sensor (TPS) is a critical component of the engine management system, and when it fails, your van's engine performance is gonna suffer.
One of the most noticeable signs that your Ford van's TP sensor has failed is the check engine light (CEL) shining nice and bright on your instrument cluster. You may also encounter one or more of the following issues:
- One of the following TPS diagnostic trouble codes (DTCs) stored in your van's computer memory:
- P0121: Throttle Position (TP) Circuit Performance Problem
- P0122: Throttle Position (TP) Circuit Low Input
- P0123: Throttle Position (TP) Circuit High Input
- Bad gas mileage
- The transmission does not upshift.
- Lack of power during acceleration
- Hesitation when pressing the accelerator pedal
- Rough idle.
- Engine stalls when stepping on the gas pedal.
- Surging.
- Engine surging is when the engine's RPM fluctuates up and down unexpectedly while you're driving or idling. It feels like the car is speeding up and slowing down on its own, even if you're keeping a steady pressure on the accelerator.
You may need a helper to perform some of these tests.
Throttle Position Sensor Circuit Descriptions
As you already may know, the throttle position sensor (TPS) on your Ford E-Series van has three wires coming out of its connector. Below are short descriptions of the signal each one carries. These are the circuit descriptions that we'll be using to test your van's TP sensor.
| Pin | Wire Color | Description |
|---|---|---|
| 1 | Brown with white stripe (BRN/WHT) | 5 Volts |
| 2 | Grey with white stripe (GRY/WHT) | TPS Signal |
| 3 | GRY/RED | Sensor Ground |
How Does The Throttle Position Sensor Work?
Here's a basic working theory to help you understand the 'why' and 'how' of the three tests you'll perform with the help of this tutorial. In a nutshell, when you crank and start the engine in your Ford van:
- The Powertrain Control Module (PCM), also known as the Fuel Injection Computer, supplies the throttle position sensor with 5 Volts and a Ground.
- This Ground is referred to as the Sensor Return in the Ford repair literature.
- When you press the accelerator pedal, the TP sensor converts the throttle plate's opening (caused by the accelerator cable) into a voltage signal the PCM can interpret.
- The PCM uses this varying voltage signal, which changes with the throttle's movement as you accelerate or decelerate, to manage fuel injection, control ignition timing, and handle all other tasks needed to keep the engine running optimally as it speeds up or slows down.
Pretty simple, right? Testing it is just as straightforward. Since you'll be working in the engine compartment, it's crucial to stay alert and be very careful. Use common sense and take all necessary safety precautions. OK, on with the show, go to: TEST 1: Testing The TPS Signal.
Where To Buy The Throttle Position Sensor And Save
The following links will help you comparison shop for the factory original Motorcraft and after-market throttle position sensor (TPS):
Not sure if the TP sensors above fit your particular Ford vehicle? Don't worry, once you get to the site, they'll make sure they fit and if they don't, they'll find you the right ones.
TEST 1: Testing The TPS Signal
To kick off our TPS sensor diagnostic, we'll start by connecting our multimeter to the grey with white (GRY/WHT) wire of the sensor's 3-wire connector and checking the TP sensor's output voltage signal.
This initial test will quickly tell us if the TP sensor is generating a variable signal that the PCM can use.
To be a bit more specific, if the TPS is functioning correctly, you should see that its voltage output rise as you open the throttle plate and fall as you close it. It's as straightforward as that!
I'm gonna recommend having someone assist you because I'm gonna ask you to lightly tap on the throttle position sensor's body with a screwdriver (or any another suitable tool) while you eye-ball your multimeter and operate the throttle. This tapping acts as a sort of TP sensor 'stress test' that'll help you further determine if it's working properly or if it has failed.
IMPORTANT: The throttle position sensor must be connected to its electrical connector for this test. You'll need to use a back probe on the connector or a wire piercing probe on the wire to see the voltage signal. You can see an example of this tool and where to buy it here: Wire Piercing Probe.
MULTIMETER RECOMMENDATION: If you don't have a digital multimeter and need to buy one, see my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
OK, let's start testing:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the GRY/WHT wire of the TP sensor 3-wire connector.
The GRY/WHT wire connects to the terminal identified with the letter 2 in the photo above.
NOTE: The TPS must remain connected to its connector to test the TPS voltage signal. - 3
Connect the black multimeter test lead directly on the battery negative (-) post.
- 4
Turn the key on but don't crank or start the engine.
- 5
Manually rotate the throttle plate.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 6
The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.
- 7
The multimeter should show a decreasing voltage as you begin to close the throttle plate.
- 8
Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.
The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps 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 interpret your test results:
CASE 1: The TPS voltage signal increased/decreased as you opened/closed the throttle plate. This is the correct test result and it indicates that the throttle position sensor is good.
With this test result you can also conclude that the TPS sensor is getting both power (5 Volts) and Ground from the fuel injection computer.
If a TPS diagnostic trouble code keeps illuminating the check engine light, see this section: TPS Code Won't Go Away for a few more suggestions as to what could be causing the TPS diagnostic trouble code (DTC).
CASE 2: The TPS voltage signal DID NOT increase/decrease as you opened and closed the throttle plate. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the BRN/WHT wire is supplying the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the BRN/WHT wire is supplying the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.