How To Test The TPS (1997-2001 4.0L V6 SOHC Ford Explorer And Mercury Moutaineer)

In this tutorial I'm gonna' explain how to test the throttle position sensor (TPS) with a multimeter.

This is a very easy test and what makes it so is that the TPS is very accessible. You'll be able to find out if the TPS is bad or not in 3 simple tests.

ES You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1997-2001 4.0L SOHC Ford Explorer) (at: autotecnico-online.com).

NOTE: This tutorial applies to the following vehicles:

• 4.0L (SOHC) Ford Explorer: 1997, 1998, 1999, 2000, 2001.
• 4.0L (SOHC) Mercury Mountaineer: 1998, 1999, 2000, 2001.

SOHC = Single Over Head Camshaft.

OTHER TPS DIAGNOSTIC TUTORIALS:

• How To Test The TPS (1991-1995 4.0L V6 Ford Explorer And Aerostar).
• How To Test The TPS (1995-2000 4.0L V6 Ford Explorer, Aerostar, And Mercury Mountaineer).

Symptoms Of A Bad Throttle Position Sensor

The throttle position sensor's job is to report the throttle plate angle as you step on or step off the accelerator pedal.

To be a bit more specific, when you step on the accelerator pedal, the throttle plate opens. When you step off the accelerator pedal, the throttle plate closes.

As the throttle plate opens and closes, the throttle position sensor sends a voltage signal to the fuel injection computer that corresponds to the throttle plate's angle.

Since the throttle position sensor is constantly monitored (when the engine is running), when it fails the fuel injection computer will set a TPS trouble code and it'll light up the check engine light. You'll see one of the following trouble codes:

• P0121: Throttle Position Sensor.
• P0122: Throttle Position Sensor.
• P0123: Throttle Position Sensor.

You're also gonna' see one or more of the following symptoms:

• Hesitation when accelerating the engine.
• Lack of power.
• Bad gas mileage.

Where To Buy The TPS And Save

The following links will help you to comparison shop for the TPS. I think they'll save you a few bucks:

Not sure if the above TPS fits your particular 4.0L SOHC Ford Explorer? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular Ford Explorer. If it doesn't fit, they'll find you the right one.

TEST 1: Testing The TPS Voltage Signal

For our first test, we're gonna' connect our multimeter to the TPS signal wire of the sensor's electrical connector.

The wire that we need to connect the multimeter to, is the gray with white stripe (GRY/WHT) wire. This wire is labeled with the number 2 in the photo above.

What we're looking for is for the TPS signal voltage to increase/decrease as we open/close the throttle plate (in the throttle body).

If the throttle position sensor is bad, it'll usually stay stuck producing a fixed voltage value as you open/close the throttle plate.

NOTE: The throttle position sensor must remain connected to its electrical connector to able to read the TPS signal voltage. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool here: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

Alright, these are the test steps:

1. 1

   Turn the key to the ON position but don't start the engine.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   Connect the red multimeter test lead to the wire labeled with the number 2.
   
   NOTE: The TP sensor must remain connected to its electrical connector.

4. 4

   Connect the black multimeter test lead to the battery negative (-) terminal.

5. 5

   Your multimeter should report a voltage between 0.2 to 0.9 Volts DC with the throttle plate closed. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.

6. 6

   Slowly open the throttle plate (by hand and from the engine compartment). The voltage numbers should increase as the throttle plate opens.
   
   This increase in voltage should be smooth and without any gaps or skips. Once the throttle plate is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.

7. 7

   Slowly close the throttle plate. As the throttle plate is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 3.

8. 8

   Lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle plate and observe the multimeter.
   
   If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.

9. 9

   Repeat step 8 several times to make sure of your multimeter test results.

Let's take a look at your test results:

CASE 1: The TPS signal voltage increased/decreased as you opened/closed the throttle plate. This is the correct test result. It tells you that the throttle position sensor IS NOT defective.

This test result also confirms that the TPS is getting both power and Ground from the fuel injection computer.

CASE 2: The TPS signal voltage DID NOT increase/decrease as you opened/closed the throttle plate. This test result usually tells you that the TPS is bad.

To make sure that the throttle position sensor is bad, you need to make sure that it's receiving power and Ground. 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 is not getting either 5 Volts or Ground.

We can easily find out if power or Ground are not reaching the throttle position sensor. Go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.

TEST 2: Making Sure The TPS Is Getting 5 Volts

The wire that feeds the throttle position sensor with 5 Volts, which are provided by the fuel injection computer, is the brown with white stripe (BRN/WHT) wire of the sensor's electrical connector.

In the photo above, I've labeled this wire with the number 1.

These 5 Volts should be present with the key ON (and of course when the engine is running).

NOTE: Be careful when probing the front of the female terminal of the TPS connector with your multimeter test leads. If the metal probe is too thick and forces its way in, it can spread or damage the terminal. Use a proper adapter or a thin back-probe tool to make the connection safely.

These are the test steps:

1. 1

   Disconnect the TPS from its electrical connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter test lead to the negative (-) battery terminal.

4. 4

   Turn the key ON but don't crank or start the engine.

5. 5

   With the red multimeter test lead, probe the female terminal that connects to the wire labeled with the #1.
   
   This wire will be the brown with white stripe (BRN/WHT) wire of the connector.

6. 6

   Your multimeter should read 4 to 5 Volts DC.

Let's take a look at what your test results mean:

CASE 1: 4 to 5 Volts are present. This is the correct and expected test result.

The next step is to make sure that the TPS is getting Ground. For this test go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: 4 to 4 Volts ARE NOT present. Without this voltage the TP sensor will not produce a TPS voltage signal.

The most likely cause of this missing voltage is an open-circuit problem in the wiring between the TP sensor connector and the fuel injection computer's connector.

Although testing this condition is beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) itself as bad.

TEST 3: Making Sure The TPS Is Getting Ground

So far you have confirmed that:

• The TPS is not producing a voltage signal that increases/decreases as you open/close the throttle plate.
• The TPS is receiving 5 Volts (TEST 2).

For our last test, we're gonna' make sure that it's getting Ground.

The wire that feeds Ground to the TP sensor is the wire labeled with the number 3 in the photo above.

This wire is the gray with red stripe (GRY/RED) wire of the sensor's electrical connector.

IMPORTANT: Ground is provided to the TP sensor by your Ford Explorer's fuel injection computer. Be careful and don't connect this wire to battery voltage (12 Volts) or you'll fry the computer. The multimeter voltage test I'm suggesting in the test steps below is a safe way to test for the presence of Ground in the wire.

OK, these are the test steps:

1. 1

   Disconnect the TPS from its electrical connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the red multimeter test lead to the positive (+) battery terminal.

4. 4

   Turn the key ON but don't crank or start the engine.

5. 5

   With the black multimeter test lead (and using the appropriate tool), probe the female terminal that connects to the wire labeled with the #3.
   
   This wire will be the gray with red stripe (GRY/RED) wire of the connector.

6. 6

   Your multimeter should read 10 to 12 Volts DC.

Let's take a look at what your test results mean:

CASE 1: Ground is present. This is the correct and expected test result.

You can conclude that the TPS is bad only if all tests have confirmed that:

• TEST 1: The TP sensor IS NOT creating a voltage signal that increases/decreases as you open/close the throttle plate.
• TEST 2: The TP sensor is being fed 5 Volts DC.
• This test section: The TP sensor is being fed Ground.

Time to replace the TPS sensor? Here's my recommendation of a well-known brand that won't let you down:

• Walker Products 200-91062 Throttle Position Sensor W/ Pigtail Connector (Amazon affiliate link).

CASE 2: Ground IS NOT present. Without Ground the TPS will not produce a TPS voltage signal.

The most likely cause of this missing Ground is an open-circuit problem in the wiring between the TP sensor connector and the fuel injection computer's connector. In the extreme of cases, the PCM has an internal problem (although this is very rare).

Although testing this condition is beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) itself as bad.

More Diagnostic Test Tutorials

You can find a complete list of 4.0L Ford Explorer, Aerostar, and Mercury Mountaineer troubleshooting tutorials here:

• 4.0L V6 Ford Explorer And Mercury Mountaineer Index of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Fuel Pump (1993-2000 4.0L V6 Ford Explorer, Aerostar, And Mercury Mountaineer).
• How To Test Engine Compression (1991-2010 4.0L V6 Ford Explorer, Aerostar, And Mercury Mountaineer).
• How To Troubleshoot A No-Start Problem (1991-2010 4.0L V6 Ford Explorer, Aerostar, And Mercury Mountaineer).
• How To Test The Fuel Injectors (1991-1996 4.0L Ford Explorer And Aerostar).