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

The throttle position sensor (TPS) on the 1996 1.9L Ford Escort or Mercury Tracer can be tested with a multimeter (no expensive diagnostic equipment needed).

In this tutorial, I'm going to explain how to check the TP sensor's output voltage signal. Then we'll make sure it's getting power (VREF) and Ground (SIG RTN) —both of which come from your Escort or Tracer's powertrain control module (PCM).

By the end of these three easy tests, you'll be able to tell if the TPS is toast and needs to be swapped out, or if it's good and the issue lies somewhere else.

APPLIES TO: This tutorial applies to the following vehicles:

• 1.9L Ford Escort: 1996.
• 1.9L Mercury Tracer: 1996.

1991-1995 TPS DIAGNOSTIC TESTS:

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

Symptoms Of A Bad Throttle Position Sensor

As you probably already know, the gas pedal is connected by an accelerator cable to the throttle plate in the throttle body. So whenever you step on or off the gas pedal, the throttle opens or closes.

The throttle position sensor (TPS) monitors the throttle plate angle and reports it to the PCM. The PCM then uses this info to calculate how much fuel needs to be injected into the engine.

When the TPS fails, the engine's gonna be in a world of hurt. You'll run into one or more of the following performance issues.

• A TPS diagnostic trouble code (DTC) stored in the FI PCM's memory:
  • P0121: Throttle Position (TP) Circuit Performance Problem.
  • P0122: Throttle Position (TP) Circuit Low Input.
  • P0123: Throttle Position (TP) Circuit High Input.
• 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.

What Tools Do I Need To Test The TPS?

All you really need is a solid multimeter and a wire-piercing probe. Below are the ones I use myself and recommend —reliable, affordable, and perfect for testing the TPS on your Ford Escort or Mercury Tracer.

TEST 1: Testing The Throttle Position Sensor Voltage Signal

The first thing we're gonna do to find out if the TPS is good or not is connect our multimeter to the TP signal output wire and see if the voltage changes as we open and close the throttle manually.

This TPS signal wire is the middle one on the connector —a gray with white stripe (GRY/WHT) wire.

Now, the one thing that'll help us figure out if the TPS is good or bad is keeping the following in mind:

• When the throttle plate opens, the TPS signal voltage increases.
• When the throttle plate closes, the TPS signal voltage decreases.

When the TPS fails, it usually stays stuck, showing a voltage value that doesn't change no matter how much we move the throttle.

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 interpret your TPS signal result:

CASE 1: The TPS voltage increases and decreases in step with the throttle plate. This is the normal behavior you're looking for. The sensor is responding correctly to throttle plate movement, so we can conclude the TPS to be working fine.

CASE 2: The throttle plate moves but the TPS voltage stays flat. That's a clear indication the sensor isn't responding.

We can't rush to replace it just yet —the next move is to confirm it's actually receiving its 5-Volt reference (VREF) signal. Head over to: TEST 2: Checking TPS Power (VREF).

CASE 3: The multimeter doesn't register any voltage at all. This doesn't automatically mean the TPS has failed, since this result could point to missing VREF power or SIG RTN Ground.

To further investigate this, head over to: TEST 2: Making Sure The TPS Is Getting Power (VREF).

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

Since in TEST 1 the throttle position voltage signal output was stuck at one value (no matter the throttle plate angle), we're now gonna make sure the sensor is getting VREF power.

The VREF 5 Volts are delivered through the light green with white stripe (LT GRN/WHT) wire —which connects to female terminal 1— from your Escort or Tracer's PCM.

Because this VREF voltage comes from the PCM, it's only available when the key is in the RUN or START position. For our test, we'll check for these 5 Volts with the key in RUN and the engine OFF.

Let's begin:

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 LT GRN/WHT wire of the connector.

6. 6

   The multimeter should show between 4.5 and 5.0 Volts DC.

Here's what your VREF power test means:

CASE 1: 4.5 and 5 Volts are present at terminal 3. That tells you the PCM is indeed supplying the throttle position sensor (TPS) with 5-Volt VREF power.

Now that VREF is verified at terminal 3, the next step is to confirm that the PCM is also providing the SIG RTN Ground. Go to: TEST 3: Making Sure The TPS Is Getting Ground (SIG RTN).

CASE 2: You don't see 4.5 to 5 Volts at terminal 3. Recheck your meter leads and run the test again just to be sure.

If the reading still shows no VREF at terminal 3, then the TPS isn't at fault —without that 5-Volt supply, the sensor can't work in the first place.

With this info, your TPS troubleshooting needs to shift toward finding out why the VREF voltage is missing and getting it restored to the circuit.

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

OK, up to this point you've checked and confirmed that: 1) the TP signal voltage is stuck regardless of throttle plate position, and 2) the sensor is getting VREF power.

For our final TPS diagnostic test, we're gonna make sure your Escort or Tracer's PCM is sending Ground to the sensor through the gray with red stripe (GRY/RED) wire at terminal 1.

This Ground, in Ford's technical jargon, is called the SIG RTN Ground, and it's only present with the key in the RUN or START position.

For our test, we'll do a multimeter voltage check at terminal 1 with the key in RUN and the engine OFF.

Alright, here we go.

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 ORG wire of the connector.

6. 6

   The multimeter should show between 10 to 12 Volts DC.

Let's interpret your SIG RTN Ground test result:

CASE 1: The meter reads 10 to 12 Volts. That confirms the PCM is delivering a solid SIG RTN Ground to the TPS.

If the following three checks all line up, then the TPS on your Escort or Tracer is faulty and needs to be replaced:

• In TEST 1, the TPS signal stayed fixed and never responded to throttle movement.
• In TEST 2, the sensor had its 5-Volt VREF at terminal 3.
• And here in TEST 3, terminal 1 shows SIG RTN Ground is present.

CASE 2: The meter doesn't show 10 to 12 Volts. Double-check your test connections and repeat the test.

If terminal 1 still has no SIG RTN Ground, the TPS isn't to blame. Without that Ground path, the sensor has no way to function.

Troubleshooting why SIG RTN is missing is beyond the scope of this tutorial, but the two most common causes are:

1. An open-circuit in the SIG RTN wire between the TPS connector and the PCM.
2. A failure inside the PCM itself (rare, but possible).

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 TPS (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).