How To Test The Throttle Position Sensor (2000-2004 2.0L SOHC Ford Focus)

In this tutorial, I'm gonna show you how to test the throttle position sensor (TPS) on the 2000-2004 2.0L SOHC Ford Focus without removing it from the throttle body.

We'll checking its output voltage signal, and making sure it's getting power and Ground. With your test results, you'll quickly know whether it's good or bad.

These three tests are done with a multimeter —no scan tool needed or any other expensive diagnostic equipment.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L SOHC Ford Focus: 2000, 2001, 2002, 2003, 2004.

TPS CODE DIAGNOSTICS: Click below to see what each one really means, the common causes, and what to check next:

• P0121 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).
• P0122 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).
• P0123 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).

Symptoms Of A Bad Throttle Position Sensor (TPS)

These are the most common signs of a failing throttle position sensor (TPS) on your Ford Focus:

• Check engine light with TPS codes:
  • P0121: Throttle Position (TP) Circuit Performance Problem.
  • P0122: Throttle Position (TP) Circuit Low Input.
  • P0123: Throttle Position (TP) Circuit High Input.
• Hesitation on acceleration: The engine stumbles or hesitates the moment you step on the gas pedal.
• Loss of power: Acceleration feels weak or inconsistent, as if the engine isn't responding the way it should.
• Bad gas mileage: A noticeable decrease in miles per gallon compared to normal.
• Hard starting: The engine cranks longer than usual before it finally fires up.
• Rough or lopey idle: Idle speed hunts up and down instead of holding steady.
• No-start condition: If TPS output voltage is stuck too high, the engine may refuse to start altogether.

The TPS trouble code lighting the check engine light on your Ford Focus provides specific info on how the sensor has failed. The following links explain each code in detail:

• P0121 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).
• P0122 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).
• P0123 TPS Code Diagnostics (2000-2004 2.0L Ford Focus).

TEST 1: Checking The Throttle Position Sensor (TPS) Signal

For our very first test, we're going to measure the sensor's output voltage signal by tapping into the middle wire of the TPS connector with a multimeter.

With the multimeter connected (and the key in the ON position but engine OFF), we'll then manually open and close the throttle plate.

We can expect to see one of two results:

• Normal operation: The voltage signal increases and decreases smoothly as the throttle plate is opened and closed.
• Faulty sensor: The voltage remains fixed at a single value instead of responding to throttle movement.

Keep in mind that the TPS must remain plugged into its 3-wire connector during the signal test. You'll need to use a back probe at the connector or a wire-piercing probe on the signal wire (to read the signal). If you don't have either tool, check out my recommendation here —it's the same one I use in my own work:

• Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

If you don't have a multimeter or need to upgrade yours? Check out my recommendation: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).

Here are the test steps:

1. 1

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

2. 2

   Set the multimeter to DC Volts mode.

3. 3

   Turn the ignition key to ON (engine OFF). Do not crank the engine.
   
   This powers up the TPS.

4. 4

   Probe the center wire of the TPS connector with the red multimeter lead, using a back probe or a wire-piercing probe.
   
   The center wire should be white (WHT).
   
   NOTE: Keep the TPS plugged into its connector during the test.

5. 5

   With the throttle plate fully closed, voltage should read between 0.3 and 0.9 Volts DC.
   
   Record this as your base reading.

6. 6

   Open the throttle plate slowly by hand. Voltage should increase smoothly as the plate opens.

7. 7

   At wide-open throttle (WOT), voltage should measure between 3.5 and 4.5 Volts DC.

8. 8

   Close the throttle plate slowly. Voltage should return to the value recorded in step 5.
   
   Confirm the closed-throttle reading matches the starting value.

9. 9

   Lightly tap the TPS housing with the handle of a screwdriver while moving the throttle plate.
   
   NOTE: Readings must remain stable. If they spike, drop out, or glitch, the TPS is defective and must be replaced.

Let's interpret that test result:

CASE 1: The TPS voltage signal rose and fell smoothly with no interruptions. This is the expected result and confirms the TPS is operating correctly.

This outcome also tells you that the sensor is receiving both power and Ground. No further testing is required.

CASE 2: The TPS voltage signal did not change with throttle movement. In most cases, this indicates a faulty TPS —but not always.

To confirm the sensor is defective, perform two more checks. The first is here: TEST 2: Making Sure The TPS Is Getting Power.

CASE 3: The TPS voltage signal showed spikes or drop-outs when the sensor was tapped. If this occurs, the TPS is faulty and must be replaced.

TEST 2: Making Sure The TPS Is Getting Power

If the TPS signal didn't rise and fall with throttle movement in TEST 1, the next step is to confirm the sensor is actually receiving power.

The TPS is powered by a 5-Volt reference supplied by the PCM. This 5V feed comes in on the yellow (YEL) wire at the TPS 3-wire connector.

In the connector pinout shown above, the YEL wire corresponds to terminal 3.

CAUTION: Gently probe the front of the female terminal on the TPS connector. Forcing the multimeter test lead in can spread the terminal, which may cause a poor connection with the TPS pin. If the terminal is damaged, the connector will need to be replaced.

This is what you need to do:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Turn the ignition key to ON (engine OFF). Do not crank the engine —we only powers the TPS circuit.

3. 3

   Set your multimeter to DC Volts mode.

4. 4

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

5. 5

   Probe terminal 3 of the TPS connector with the red multimeter lead.
   
   NOTE: Terminal 3 is the 5-Volt reference supply. It should be the yellow (YEL) wire.

6. 6

   Your multimeter should read between 4.5 and 5.0 Volts DC.

Here's how to interpret your results:

CASE 1: The multimeter shows 4.5 to 5 Volts. This is the correct reading and confirms the TPS is receiving power from your Focus' PCM.

The next step is to verify the sensor also has Ground. Go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: No voltage is present. Double-check that you're probing the correct terminal, then repeat the test.

If there's still no 4.5 to 5 Volts, the TPS itself is not at fault. Without the 5-Volt reference, the sensor cannot operate.

Although finding the cause of the missing voltage is outside the scope of this tutorial, your next step is troubleshoot the cause and fix it to get the TPS functioning again. In most cases, the problem is an open-circuit problem in the 5-Volt supply wire between the TPS connector and the PCM.

TEST 3: Making Sure The TPS Is Getting Ground

So far in your TPS diagnostic, you've confirmed two things:

• TEST 1: The TPS is not producing a voltage signal that rises and falls as the throttle plate is opened and closed.
• TEST 2: The TPS is receiving its 5-Volt reference.

For the final check, we need to make sure the TPS also has Ground.

This Ground is provided by the PCM. It runs through the brown (BRN) wire at the TPS connector and connects to the female terminal marked number 1 in the pinout diagram shown above.

We'll verify this with a simple multimeter voltage test. This test will confirm whether Ground is present or not (in the circuit).

IMPORTANT: Use caution when testing this circuit. The Ground wire connects directly to the PCM. Never apply battery 12 Volts to it, or you risk frying the PCM. The voltage test outlined below is the safe way to check for Ground.

OK, let's get started:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Turn the ignition key to ON (engine OFF). Do not crank or start the engine —this step only powers the TPS circuit.

3. 3

   Set your multimeter to DC Volts mode.

4. 4

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

5. 5

   Probe terminal 1 of the TPS connector with the black multimeter lead.
   
   NOTE: Terminal 1 is the Ground circuit. It should be the brown (BRN) wire at the connector.

6. 6

   The multimeter should display between 10 and 12 Volts DC if the PCM is supplying the TPS with Ground.

Now, let's look at the results:

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

You can confirm the TPS is defective and must be replaced if all three of the following conditions are true:

• In TEST 1, the TPS did not produce a voltage signal that rose and fell with throttle movement.
• In TEST 2, the TPS was confirmed to be receiving 5 Volts.
• In this test, the TPS is confirmed to have Ground.

CASE 2: Ground IS NOT present. Make sure you're testing the correct terminal and repeat the test.

If the multimeter still doesn't show 10 to 12 Volts DC, you can rule out the TPS as the problem. Without a Ground circuit, the sensor can't operate.

Troubleshooting this missing Ground issue is outside the scope of this tutorial, but the fix will involve locating and repairing the problem so the TPS can work again.

In most cases, the loss of Ground is caused by an open-circuit issue in the Ground wire between the TPS connector and the PCM.

More 2.0L Ford Focus Diagnostic Tutorials

You can find a complete list of tutorials and wiring diagrams for the 2.0L Ford Focus in this index:

• 2.0L Ford Focus Index Of Articles.