How To Test The Throttle Position Sensor (1995-2004 4.6L Crown Victoria, Grand Marquis)

The throttle position sensor (TPS) is probably one of the easiest sensors you can test with just a multimeter and determine if it's good or bad.

In this tutorial, I'll show you the three to tests you can do with a multimeter that'll tell you 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.

APPLIES TO: Applies to the following gasoline powered vehicles:

• 4.6L Ford Crown Victoria: 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004.
• 4.6L Mercury Grand Marquis: 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004.

Symptoms Of A Bad Throttle Position Sensor

The throttle position sensor (TPS) plays a critical role in the engine management system, and if it fails, your Crown Vic or Grand Marquis' engine performance will suffer.

One of the most obvious signs that the TP sensor has failed is the check engine light (CEL) illuminating on the instrument cluster. You might also encounter one or more of the following symptoms:

• One of the following TPS diagnostic trouble codes (DTCs) stored in the PCM'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

The throttle position sensor has three wires and each one has a specific job to do. Below you'll find brief descriptions of the signals transmitted by each wire:

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?

The one thing that's gonna help you easily diagnose the TP sensor as good or bad is knowing a little about how it works. With this info, you'll also be able to understand the 'why' and 'how' of the three tests I'm gonna show you how to do in this tutorial. In a nutshell, when you crank and start the engine:

• The throttle position sensor receives 5 Volts and Ground from the fuel injection computer (also known as the Powertrain Control Module or PCM for short).
  • This voltage and Ground activates the TP sensor.
  • In Ford's repair literature, the Ground that any sensor receives is referred to as 'sensor return'.
• When you step on the accelerator pedal, the throttle cable causes the throttle plate (in the throttle body) to open. The TP sensor instantly converts its opening into a voltage signal that the PCM can use.
• As the TP sensor's voltage signal changes due to the throttle plate's movement when you step on or off the accelerator pedal, the PCM uses this changing voltage signal to control fuel injection, manage ignition timing, and perform other necessary tasks to keep the engine running smoothly.

Pretty simple, right? The three tests I'm gonna explain in the next sections is just as straightforward. 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 this show on the road, we'll connect a multimeter to the grey with white stripe (GRY/WHT) wire of the sensor's 3-wire connector and check the TP sensor's output voltage signal.

This first test will quickly tell us if the TP sensor generates a variable signal that changes in response to the throttle plate movement (as we manually open and close it).

Specifically, if the TPS is working correctly, its voltage output should increase as you open the throttle plate and decrease as you close it. It's that easy and simple!

To further make sure the TP sensor is OK, I'm also gonna ask you to lightly tap on the throttle position sensor's body with a screwdriver' handle while you keep an eye on your multimeter and as you open/close the throttle plate.

Lightly tapping the sensor with a screwdriver kinda acts as a sort of 'stress test' that'll help you 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 (this is the one I use) and where to buy it here: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

MULTIMETER RECOMMENDATION: If you don't have a digital multimeter and need to buy one, see my recommendations here: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).

OK, let's start testing:

1. 1

   Place your multimeter in Volts DC mode.

2. 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. 3

   Connect the black multimeter test lead directly on the battery negative (-) post.

4. 4

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

5. 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. 6

   The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.

7. 7

   The multimeter should show a decreasing voltage as you begin to close the throttle plate.

8. 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.

TEST 2: Making Sure The TPS Is Getting 5 Volts

Now that you've confirmed that the TP sensor isn't creating a variable voltage signal, we'll need to check that it's getting 5 Volts DC. As mentioned earlier, these 5 Volts are supplied by the PCM.

It's the brown with white stripe (BRN/WHT) wire of the sensor's 3-wire connector that delivers this voltage and the one that we're gonna test in this section.

If the BRN/WHT wire is supplying power to the TP sensor, you'll see a reading of 4.5 to 5 Volts DC on your multimeter.

Let's get started:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

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

3. 3

   Put your multimeter in Volts DC mode.

4. 4

   Turn the key to its ON position but do not start the engine.

5. 5

   Gently probe the female terminal labeled with the number 1 with the red multimeter test lead (see photo above).
   
   This female terminal should connect to the BRN/WHT wire of the 3-wire connector.

6. 6

   Your multimeter should read 4.5 to 5 Volts.

Let's analyze your test results:

CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct 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: The multimeter DID NOT register 4.5 to 5 Volts. This result tells you that the TP sensor is not getting the power it needs to function.

This missing voltage is generally the result of an open-circuit problem in the the BRN/WHT wire or the PCM is fried (not very common).

Altho testing these two conditions is beyond the scope of this tutorial, you have now eliminated the throttle position sensor (TPS) itself as faulty.

TEST 3: Making Sure The TPS Is Getting Ground

So far, the results of the previous two tests have confirmed:

• The TPS isn't producing a voltage signal that changes as you open or close the throttle plate (TEST 1).
• The TPS is getting 5 Volts DC from the PCM (TEST 2).

For our final TP sensor test, we'll check that the grey with red stripe (GRY/RED) is supplying it with Ground.

A simple multimeter voltage test will do to help us confirm that Ground is present in the GRY/RED wire.

NOTE: The PCM provides this Ground, so be careful not to connect this wire to battery power (12 Volts), whether intentionally or accidentally, as this will damage the PCM. The multimeter voltage test I'm recommending in the instructions is a safe way to check for Ground in the GRY/RED wire.

OK, let's start:

1. 1

   Disconnect the TP sensor from its 3-wire connector.

2. 2

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

3. 3

   Put your multimeter in Volts DC mode.

4. 4

   Turn the key to its ON position but do not start the engine.

5. 5

   Gently probe the female terminal labeled with the number 3 with the red multimeter test lead (see photo above).
   
   This female terminal should connect to the GRY/RED wire of the 3-wire connector.

6. 6

   Your multimeter should read 10 to 12 Volts.

Let's interpret your test results:

CASE 1: The multimeter registered 10 to 12 Volts. This test result confirms the TP sensor is being supplied with Ground (from the PCM).

You can conclude that the TPS is bad and needs to be replaced if you have:

• Confirmed the TPS is not producing a voltage signal that increases/decreases as you open/close the throttle plate (TEST 1).
• Confirmed the TPS is getting 5 Volts DC from the PCM (TEST 2).
• Confirmed the TPS is getting Ground from the PCM (this test section).

CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result lets you know that the TPS is not getting Ground.

This missing Ground is generally the result of an open-circuit problem in the the GRY/RED wire or the PCM is fried (not very common).

Although testing these two conditions is beyond the scope of this tutorial, you have now ruled out the throttle position sensor (TPS) itself as the problem.

TPS Code Won't Go Away

If the TP sensor tested good or you've replaced it, but the TPS diagnostic trouble code keeps coming back and illuminating the check engine light, I've compiled a list of possible issues that could be causing this problem:

• The throttle plate's idle-stop screw might've been adjusted to 'solve' a misfire or rough idle condition, leading to a higher idle speed. This adjustment raises the TP sensor's signal to the PCM, which doesn't like it and triggers the check engine light (CEL).
• The throttle cable could be sticking, stopping the throttle plate from fully closing. You can check this by having a helper step on and off the accelerator pedal (with the engine OFF) while you check the throttle plate and cable's movement.
• The TPS may be failing intermittently. What I mean is that it may work fine most of the time but occasionally it may stop generating a variable voltage signal.
  
  The best way to check for these intermittent problems is by road-testing the vehicle with the multimeter connected to the TP signal wire, using a long jumper-wire so you can comfortably watch the signal changes while someone else drives.
• The TP sensor's connector is damaged. The most common problem is that its locking tab has broken off, causing the connector to loosen while the engine runs and creating an intermittent false connection.

More 4.6L Crown Victoria And Grand Marquis Tutorials

If this tutorial was helpful, be sure and take a look at all of the 4.6L Ford Crown Vic and Mercury Grand Marquis diagnostic tutorials and wiring diagrams in this index:

• 4.6L Crown Victoria And Grand Marquis Index of Articles.

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

• How To Test Engine Compression (1992-2011 4.6L Crown Victoria, Grand Marquis).
• Blown Head Gasket Tests (1992-2011 4.6L Crown Victoria, Grand Marquis).
• How To Test The Fuel Injectors (1992-1997 4.6L Crown Victoria, Grand Marquis).