How To Test The Throttle Position Sensor (1991-1995 1.9L Ford Escort, Mercury Tracer)

One of the cool things about diagnosing the throttle position sensor (TPS) on your 1991–1995 1.9L Ford Escort or Mercury Tracer is that you don't need any fancy or expensive diagnostic equipment. You can test the sensor with just a multimeter.

In this tutorial, I'm going to show you how to check the TPS output signal voltage, and make sure it's getting both power (5V VREF) and Ground (SIG RTN).

With these three basic tests, you'll quickly find out if the TPS is good and doing its job —or if it's toast and needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 1.9L Ford Escort: 1991, 1992, 1993, 1994, 1995.
• 1.9L Mercury Tracer: 1991, 1992, 1993, 1994, 1995.

1996 TPS SENSOR DIAGNOSTIC TESTS:

• How To Test The Throttle Position Sensor (1996 1.9L Ford Escort, Mercury Tracer).

Symptoms Of A Bad Throttle Position Sensor

The throttle position sensor (TPS) is the go-to sensor your Escort or Tracer's fuel injection (FI) computer relies on to know how much the throttle opens or closes as you step on or off the gas pedal.

Because the TPS is a critical part of the engine management system, when it fails, it's gonna wreak havoc on your Escort or Tracer's performance. You'll usually see one or more of the following symptoms:

• A TPS diagnostic trouble code (DTC) stored in the FI computer's memory:
  • 121: TPS Voltage Higher Or Lower Than Expected.
  • 122: TPS Circuit Below Minimum Voltage.
  • 123: TPS Circuit Above Maximum Voltage.
  • 124: TPS Voltage Higher Than Expected.
  • 125: TPS Voltage Lower Than Expected.
• Your Escort or Tracer fails the smog check (state mandated emissions test).
• Bad gas mileage.
• Hard start, in other words extended cranking time.
• Black smoke coming out of the tailpipe.
• Hesitation when accelerating your vehicle down the road.

Thankfully, the TPS can be tested without a scan tool and in this tutorial, I'll show you how.

Where To Buy Your TP Sensor And Save

When you're ready to replace the throttle position sensor on your 1991-1995 1.9L Escort or Tracer, I want to recommend the TPS from Walker Products. This is a solid brand that I have used over the years and recommend.

Not sure if the above TP sensor fits your particular 1991-1995 1.9L equipped Ford Escort? 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 Throttle Position Sensor Voltage Signal

To successfully troubleshoot the TPS as good or bad, we need to know two key things:

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

The cool thing is, we can easily verify that the TPS is reacting to throttle plate movement by tapping into its signal wire with a multimeter. Then, by manually opening and closing the throttle, we can watch to see if the sensor responds.

The wire, we're going to tap into is the middle wire of the TPS 3-wire connector. Depending on your Escort or Tracer's year model, this wire will be:

• 1991–1992: Dark green with light green stripe (DK GRN/LT GRN).
• 1993–1995: Gray with white stripe (GRY/WHT).

If the TPS is bad, its voltage signal will stay stuck at one value, no matter how much you open or close the throttle plate.

NOTE: To check the TP signal voltage, the sensor must stay connected to its connector. You'll need to either back probe the connector or use a wire-piercing probe on the signal wire to check the voltage. If you don't have one, this is the one I use and recommend without hesitation: 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 DK GRN/LT GRN (1991-1992) or a GRY/WHT (1993-1995) 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.

Now let's break down what your multimeter just told you:

CASE 1: The TPS voltage rises and falls smoothly with the throttle plate movement. That's exactly what you want to see. The sensor is tracking throttle plate movement the way it should, so at this point you can call the TPS good.

CASE 2: The TPS signal voltage never changes as you open or close the throttle. It's starting to look like the TP sensor is bad.

Our next step is to make sure it's actually being fed its 5-Volt reference (VREF) from the FI computer. Go to: TEST 2: Making Sure The TPS Is Getting Power (VREF).

CASE 3: The multimeter shows no TPS signal voltage. This isn't good but it doesn't automatically condemn the TPS as bad.

This test result can also mean the sensor isn't getting VREF power or SIG RTN Ground in the first place. For the next test, head over to: TEST 2: Making Sure The TPS Is Getting Power (VREF).

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

Like any other electrical component on your Ford Escort or Mercury Tracer, the TPS needs both power and Ground to function.

In this section, we're going to make sure it's getting 5 Volts (VREF) from the fuel injection computer.

Depending on the year of your vehicle, this VREF voltage will come through the following wire:

• 1991-1992: Orange with white stripe (ORG/WHT).
• 1993-1994: Light green with white stripe (LT GRN/WHT).
• 1995: Brown with white stripe (BRN/WHT).

No matter the wire color, the terminal carrying these 5 Volts is female terminal 1 of the TPS 3-wire connector.

We'll do a quick multimeter test at terminal 1 and check for 5 Volts with the key ON and the engine off.

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 1 with the red multimeter lead
   
   NOTE: Check that terminal 1 connects to the BRN/WHT wire of the connector.

6. 6

   The multimeter should show between 4.5 and 5.0 Volts DC.

Here's how to read your results:

CASE 1: You see 4.5 to 5 Volts at terminal 1. This confirms the PCM is sending VREF power to the throttle position sensor (TPS).

With VREF voltage confirmed, the next step is to make sure the PCM is also supplying the SIG RTN Ground. Head over to: TEST 3: Making Sure The TPS Is Getting Ground (SIG RTN).

CASE 2: No 4.5 to 5 Volts at terminal 1. Double-check your multimeter connections and repeat the test.

If there's still no VREF power at terminal 1, the TPS itself isn't the issue —without this 5-Volt feed, it can't function at all.

Your TP sensor diagnostic now needs to focus on finding out why this VREF voltage is missing and restoring it to the circuit.

TEST 3: Making Sure The TPS Is Getting Ground (SIG RTN)

Your previous two tests have confirmed the following:

• The sensor's output signal voltage is stuck, regardless of throttle plate angle (TEST 1).
• The sensor is getting VREF power from the computer (TEST 2).

For your final diagnostic test, you're going to make sure the TPS is getting Ground from the fuel injection computer.

This SIG RTN Ground is delivered to female terminal 3 by the following wire:

• 1991-1992: Black with white stripe (BLK/WHT).
• 1993-1995: Gray with red stripe (GRY/RED).

The SIG RTN Ground is only available with the key in the RUN or START position. For our test, we'll check it with the key in the RUN position and the engine off.

CAUTION: This Ground circuit comes directly from the FI computer. Don't apply 12 Volts from the battery here, or you'll instantly fry the computer. The multimeter voltage test I'm outlining below is the safe way to check for the presence of SIG RTN Ground in this circuit.

Alright, let's get the ball rolling:

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 3 with the black multimeter lead
   
   NOTE: Check that terminal 3 connects to the BLK/WHT (1991-1992) or GRY/RED (1993-1995) wire of the connector.

6. 6

   The multimeter should show between 10 to 12 Volts DC.

Now, let's see what your test result indicates:

CASE 1: Your multimeter shows 10 to 12 Volts. That tells you the FI computer is providing the TPS with a solid SIG RTN Ground.

Your Escort or Tracer's TPS is bad and needs to be replaced if you have confirmed:

• In TEST 1, the TPS signal never moved with throttle plate changes.
• In TEST 2, the sensor is receiving VREF power at terminal 1.
• And here (in TEST 3), terminal 3 has SIG RTN Ground present.

When you're ready to replace it, here's the TPS I recommend:

• Walker Products 200-1058 Throttle Position Sensor (Amazon affiliate link).

CASE 2: Your multimeter didn't show 10 to 12 Volts. Recheck your multimeter test connections, then run the test again.

If there's still no SIG RTN Ground at terminal 3, you can rule out the TP sensor as bad. Without that Ground feed, the sensor simply can't operate.

Troubleshooting this missing SIG RTN Ground goes beyond this tutorial, but here are the two usual suspects:

1. A break (open) in the SIG RTN wire between the TPS connector and the FI computer.
2. An internal fault inside the computer itself (very rare).

More 1.9L Ford Escort And Mercury Tracer Diagnostic Tutorials

You can find a complete list of 1.9L Ford Escort and Mercury Tracer tutorials in this index:

• 1.9L Ford Escort Index Of Articles.

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

• How To Test The MAF Sensor (1991-1995 1.9L Ford Escort, Mercury Tracer).
• Common Causes Of Spark Plug Failure (1991-1995 1.9L Ford Escort, Mercury Tracer).
• How To Test For A Blown Head Gasket (1991-1995 1.9L Ford Escort, Mercury Tracer).
• How To Test Engine Compression (1991-1995 1.9L Ford Escort, Mercury Tracer).