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

When the TPS fails on your 2.0L Ford Escort ZX2 the engine's performance is going to suffer and the check engine light is gonna' shine nice and bright.

Fortunately for the DIY'er, the throttle position sensor (TPS) can tested with a simple multimeter to find out if it's bad or not.

In this tutorial, I'll show you how it's done in a step-by-step way and in plain English.

You can find this tutorial in Spanish here: Verificando El Sensor TPS (2.0L Ford Escort ZX2) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L DOHC Ford Escort ZX2: 1998, 1998, 1999, 2000, 2001, 2002, 2003.

Symptoms Of A Bad Throttle Position Sensor

A failed throttle position sensor (TPS) will light up the check engine light (CEL) on your 2.0L Ford Escort ZX2.

You'll also see one or more of the following symptoms:

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 ZX2 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.

What Tools Do I Need To Test The TPS Sensor?

To test the TP sensor on your 1998-2003 2.0L DOHC Ford Escort ZX2, you'll need two important tools (nothing that's gonna break the bank), and these are:

• A multimeter: To check the TPS signal voltage output, and verify power (VREF) and Ground (SIG RTN) to the sensor.
• A wire-piercing probe or back probe: This tool lets you access the TPS signal voltage inside the signal wire in TEST 1.

In the links below, you'll find the same multimeter I've used for years. It's a reliable tool that delivers accurate readings, and it has every feature you'll need for testing a TP sensor or just about any other electrical component on your vehicle.

I also pointing you to the wire-piercing probe kit I rely on. It's inexpensive, practical, and you can use it either as a wire-piercing probe or flip it around for back-probing when that works better for the job.

TEST 1: Testing The TPS Voltage Signal

The TPS engine wiring harness connector has 3 wires coming out of it. The wire that carries the throttle angle voltage signal is the middle one.

This middle wire is the gray with white stripe (GRY/WHT) wire and this is the one that we're gonna' tap into with a multimeter.

What we're gonna' verify is that the TP signal voltage increases when we open the throttle plate and then decreases when we close the throttle plate. It's as simple as that!

IMPORTANT: The throttle position sensor has to remain connected to its connector for this test to work (this is where a wire piercing probe comes in handy to get to the signal inside the wire. To see what one looks like, click here: 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. This confirms that your 2.0L Ford Escort ZX2's TP sensor is OK and not defective.

CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This tells you that the TPS is bad and causing the TPS trouble code lighting up the check engine light (CEL) on your 2.0L Ford Escort ZX2.

Before you run out and buy it, I'm gonna' suggest that you do two more tests. One is to check that the TPS is getting power. The other is to check that it's Ground. To check that the TPS is getting power, go to: TEST 2: Making Sure The TPS Is Getting Power.

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 power or 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.

TEST 2: Making Sure The TPS Is Getting Power

So far you have confirmed that the TPS is not producing an increasing/decreasing throttle position voltage signal. The next step is to make sure that it's getting power (5 Volts DC).

The wire that feeds this VREF power is the brown with white stripe (BRN/WHT) wire of the TPS engine wiring harness connector.

To check for these 5 Volts all we need to do is a very simple multimeter voltage test. So, without further ado, let's get testing:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Switch the key to the ON position (engine off). Don't crank or start the engine.

3. 3

   Put your multimeter in Volts DC mode.

4. 4

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

5. 5

   Gently probe the front of the female terminal that connects to the BRN/WHT wire with the red multimeter lead.

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: The BRN/WHT wire has 4.5 to 5 Volts. This means that the throttle position sensor (TPS) is getting power from your 2.0L Ford Escort ZX2's fuel injection computer.

The next and last test, is to make sure that the throttle position sensor is getting Ground (from the PCM too). For this test, go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: The BRN/WHT wire DOES NOT have 4.5 to 5 Volts. Double check all of your connections and repeat the test.

If your multimeter still doesn't register the 4.5 to 5 Volts DC, then this test result tells you that the TPS itself is not at fault (and thus causing the TPS trouble code). Without power, the TPS can't create a throttle angle voltage signal. Although beyond the scope of this tutorial, your next step is to diagnose and restore this missing power.

TEST 3: Making Sure The TPS Is Getting Ground

In this last test, we're gonna check that the gray with red stripe (GRY/RED) wire of the TPS engine wiring harness connector is feeding the TPS with Ground (SIG RTN).

Since SIG RTN Ground is provided by the PCM, the safest way to check for it is with multimeter voltage test.

IMPORTANT: Ground is provided directly by the fuel injection computer. Be careful and don't intentionally or accidentally short this wire (circuit) to battery power or you'll fry the fuel injection computer.

OK, here are the test steps:

1. 1

   Disconnect the TPS from its 3-wire connector.

2. 2

   Switch the key to the ON position (engine off). Don't crank or start the engine.

3. 3

   Put your multimeter in Volts DC mode.

4. 4

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

5. 5

   Gently probe the front of the female terminal that connects to the GRY/RED wire with the red multimeter lead.

6. 6

   The multimeter should show between 10 to 12 Volts DC.

Let's find out what your test result means:

CASE 1: The multimeter registered 10 to 12 Volts, confirming the GRY/RED is feeding Ground to the TPS. This is the correct and expected test result and confirms the TPS is getting Ground.

Taking into account the test results of all 3 test, you have confirmed that:

1. The TP sensor is not providing a varying voltage signal when manually opening the throttle plate (TEST 1).
2. The TP sensor is being fed 5 Volts DC (TEST 2).
3. The TP sensor is being fed Ground (TEST 3).

Therefore, you can conclude that the throttle position sensor is bad and needs to be replaced (and that this will solve the TP sensor code lighting up the check engine light).

CASE 2: The multimeter DID NOT register 10 to 12 Volts, confirming the GRY/RED IS NOT feeding Ground to the TPS. Double check that you're testing the correct TP sensor harness terminal wire and repeat the test.

If your test result still indicates that the TPS is not getting Ground, then we can conclude that one of two things are causing this lack of Ground:

1. There's an open in the wire between the TP sensor harness connector and the fuel injection computer's harness connector.
2. The fuel injection computer has an internal problem (although this is extremely rare).

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 2.0L Ford Escort ZX2 as being the cause of the problem and/or the TP sensor diagnostic trouble code (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 Throttle Position Sensor (1998-2003 2.0L Ford Escort ZX2).