How To Test The Throttle Position Sensor (1997-2002 2.0L SOHC Ford Escort, Mercury Tracer)

The throttle position sensor (TPS) on your 1997-2002 2.0L (SOHC) Ford Escort or Mercury Tracer is pretty easy to test.

You don't need any expensive diagnostic equipment. In fact, you don't even need a scan tool —all you need is a multimeter.

In this tutorial, I'm going to show you how to check that the sensor's output signal (TPS) voltage is OK, and we'll also make sure it's getting both power (VREF) and Ground (SIG RTN).

By the end of these tests, you'll be able to quickly confirm whether the sensor is OK or if it's toast and needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L SOHC Ford Escort: 1997, 1998, 1999, 2000, 2001, 2002.
• 2.0L SOHC Mercury Tracer: 1997, 1998, 1999.

TPS TEST (1998-2003 2.0L DOHC ESCORT ZX2):

• How To Test The Throttle Position Sensor (1998-2003 2.0L Ford Escort ZX2).

Symptoms Of A Bad Throttle Position Sensor

One of the key inputs your Escort or Tracer's PCM needs to keep the engine running is the actual throttle angle as you step on or off the gas pedal. And as you guessed it, the TPS is the one responsible for providing this info.

When the TPS fails, the engine is going to be in all kinds of hurt. You'll usually see one or more of the following performance issues:

1. A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
   • P0121: Throttle Position (TP) Circuit Performance Problem.
   • P0122: Throttle Position (TP) Circuit Low Input.
   • P0123: Throttle Position (TP) Circuit High Input.
2. Your 2.0L Ford Escort or Tracer fails the smog check (state mandated emissions test).
3. Bad gas mileage.
4. Hard start and/or extended cranking time (after shut off).
5. Black smoke coming out of the tailpipe.
6. Hesitation when accelerating your vehicle down the road.

Thankfully, the TPS can be tested without a scan tool and in the next section we'll start with the very first test.

Where To Buy Your TP Sensor And Save

The throttle position sensor on your Ford Escort or Mercury Tracer isn't an expensive engine management component, but it never hurts to save money. The following links are to sensors from well-known automotive brands I've used for years and don't hesitate to recommend:

Not sure if the above TP sensor fits your particular 2.0L (SOHC) equipped Ford Escort or Mercury Tracer? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.

TEST 1: Testing The TPS Voltage Signal

All right, to get this show on the road, we're going to tap into the TPS signal wire and check its output.

To wrap our heads around the TPS signal test, here's what we need to know:

• When the throttle plate opens —like when you step on the gas pedal— the TPS signal voltage increases.
• When you let off the gas pedal, the voltage decreases.

This behavior is so predictable that we can easily check it, and that's exactly what we're going to do for our first TPS diagnostic test.

Now, when the TPS fails, it usually stays stuck at one voltage value no matter how much you move the throttle.

IMPORTANT: The throttle position sensor must stay connected to its connector for this test to work. This is where a wire-piercing probe or a back probe comes in handy to access the signal inside the wire. This is the one I use and recommend: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

OK, let's start:

1. 1

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

2. 2

   Set your multimeter to DC Volts mode.

3. 3

   Turn the key to the ON position (engine OFF). Don't crank or start the engine.
   
   This step powers up the TPS.

4. 4

   Probe the middle wire of the TPS connector with the red multimeter test lead and an appropriate tool (like a back probe or a wire-piercing probe).
   
   The middle wire of the TPS connector should be a gray with white stripe (GRY/WHT) wire.
   
   NOTE: The TPS must stay connected to its 3-wire connector during this test.

5. 5

   With the throttle plate completely closed, the voltage should read between 0.3 and 0.9 Volts DC.
   
   This is your base reading.

6. 6

   Open the throttle plate slowly by hand. The voltage should climb smoothly as the plate opens.

7. 7

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

8. 8

   Close the throttle plate slowly. The voltage should fall back down to the same number you recorded in step 5.
   
   Verify that the closed-throttle reading matches your starting value.

9. 9

   Lightly tap the TPS body with the handle of a screwdriver while opening and closing the throttle plate.
   
   NOTE: Tapping on the sensor should not cause the readings to spike, cut out, or glitch. If it does, the TPS is faulty and must be replaced.

Let's take a look at your test results:

CASE 1: The throttle angle voltage increased and decreased as you opened and closed the throttle plate. Great! This is exactly what we needed to see and it tells you your Escort or Tracer's TP sensor is OK and doing its job.

If a P0122 or P0123 diagnostic trouble code was originally registered, the condition that caused it isn't present right now —since the TPS isn't stuck low or high and is responding to throttle plate movement.

CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This isn't good, but we can't call the TPS bad just yet.

Before buying and replacing it, we need to do two more checks: one to make sure it's getting VREF power, and another to make sure it's getting SIG RTN Ground. For the first of these two tests, go to: TEST 2: Making Sure The TPS Is Getting Power (VREF).

CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the TP sensor as bad just yet.

Why? Because the TP sensor may be missing either VREF power or SIG RTN Ground. So the next step is to check that the TP sensor is getting power, go to: TEST 2: Making Sure The TPS Is Getting Power (VREF).

TEST 2: Making Sure The TPS Is Getting Power (VREF)

At this point, you've confirmed the TPS isn't producing a changing voltage signal in TEST 1.

The next step is to verify it's receiving its VREF power supply (5 Volts DC). Without it, the TPS can't generate a variable voltage signal that tracks the throttle plate angle.

This VREF voltage comes in on the brown with white stripe (BRN/WHT) wire, which connects to female terminal 3 of the TPS connector.

Checking it is easy —we'll just do a quick multimeter voltage test at terminal 3.

Let's get testing:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Switch the key to the RUN position (ON) but don't crank or start the engine.

3. 3

   Set your multimeter to Volts DC mode.

4. 4

   Connect the black multimeter test lead to the battery's negative (-) post.

5. 5

   Gently probe the front of female terminal 3 with the red multimeter lead
   
   NOTE: Check that terminal 3 connects to the BRN/WHT wire of the connector.

6. 6

   The multimeter should show between 4.5 and 5.0 Volts DC.

Let's take a look at your test results:

CASE 1: 4.5 to 5 Volts are present at terminal 3. This confirms that VREF power is being supplied from the PCM to your Escort or Tracer's throttle position sensor.

Next, we need to make sure the sensor is also receiving SIG RTN Ground, which is supplied by the PCM as well. For that check, go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: 4.5 to 5 Volts are NOT present at terminal 3. Double-check your multimeter connections and repeat the test.

If VREF power (4.5 to 5 Volts DC) is still missing at terminal 3, the TPS itself isn't the problem —it can't produce a throttle angle signal without it.

Tracking down and restoring that missing VREF voltage is beyond the scope of this tutorial, but that's where you'll need to focus your troubleshooting efforts.

TEST 3: Making Sure The TPS Is Getting Ground

Your previous two tests show that:

• The TPS signal is stuck at one value regardless of throttle plate angle (TEST 1).
• The TPS is getting VREF voltage (TEST 2).

In this final test, we'll check that the gray with red stripe (GRY/RED) wire at the TPS connector is supplying SIG RTN Ground.

This Ground should be present at terminal 1, which is the terminal of the TPS connector the GRY/RED wire connects to.

Because the PCM provides this Ground, it will only show up with the key in the ON position. One of the safest ways to check it is with a multimeter voltage test.

IMPORTANT: This Ground comes directly from the fuel injection computer. Never short this circuit to battery power —doing so will deep-fry your Escort or Tracer's PCM.

OK, here are the test steps:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Switch the key to the RUN position (ON) but don't crank or start the engine.

3. 3

   Set your multimeter to Volts DC mode.

4. 4

   Connect the red multimeter test lead to the battery's positive (+) post.

5. 5

   Gently probe the front of female terminal 1 with the black multimeter lead
   
   NOTE: Check that terminal 1 connects to the GRY/RED wire of the connector.

6. 6

   The multimeter should show between 10 to 12 Volts DC.

Let's find out what your test result means:

CASE 1: The SIG RTN Ground is present at terminal 1. This result confirms the TPS is getting its SIG RTN Ground like it should.

The TPS is fried and needs to be replaced only if you have confirmed all of the following:

1. The TPS signal is stuck at one value regardless of throttle movement (TEST 1).
2. The TPS is receiving VREF voltage (TEST 2).
3. The TPS is receiving SIG RTN Ground from the PCM (this test).

CASE 2: The SIG RTN Ground is NOT present at terminal 1. Double-check that you're probing the correct terminal on the TPS connector and repeat the test.

If the result is still the same, the missing SIG RTN Ground is caused by one of two things:

1. An open in the GRY/RED wire between the TPS connector and the PCM connector.
2. An internal problem in the PCM itself (although this is extremely rare).

Testing these two possibilities is beyond the scope of this tutorial. But at this point, you've confirmed the TPS itself is not the cause of the problem or the TPS-related DTC lighting up the check engine light (CEL).

More 2.0L Ford Escort And Mercury Tracer Diagnostic Tutorials

You can find a complete list of 2.0L Ford Escort and Mercury Tracer tutorials in this index:

• 2.0L Ford Escort Index Of Articles.

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

• How To Test Engine Compression (1997-2003 2.0L Ford Escort, Mercury Tracer).
• Common Causes Of Spark Plug Failure (1997-2003 2.0L Ford Escort, Mercury Tracer).
• How To Test For A Blown Head Gasket (1997-2003 2.0L Ford Escort, Mercury Tracer).
• How To Test The MAF Sensor (1997-2002 2.0L SOHC Ford Escort, Mercury Tracer).