How To Test The Throttle Position Sensor (1989-1997 1.6L Toyota Corolla)

This tutorial will help to test the throttle position sensor on your 1989 to 1997 1.6L Toyota Corolla with a simple multimeter.

The throttle position test outlined in this tutorial will help you to accurately diagnose the TPS as bad (or not).

NOTE: The throttle position sensor on the 1989 to 1997 Toyota Corolla (1993-1997 Geo Prizm) is two components in one assembly. One part is the throttle position sensor and the other is and idle switch. This tutorial only troubleshoots the TPS part of the TPS assembly.

If you need to test the idle switch part of the TPS, this tutorial will help: TPS Idle Switch Multimeter Test (1.6L Toyota Corolla).

ES You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1.6L Toyota Corolla) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 1.6L (4A-FE) Toyota Corolla: 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.
• 1.6L (4A-GE) Toyota Corolla: 1989, 1990, 1991.
• 1.6L Geo Prizm: 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.

Symptoms Of A Bad Throttle Position Sensor

The fuel injection system on your 1.6L Toyota Corolla (Geo Prizm) will be either an OBD I or an OBD II (depending on your vehicle's specific year model). Either On-Board-Diagnostic (OBD) systems are designed to set a throttle position sensor trouble code when the sensor fails.

Here's a basic list of symptoms you'll see:

1. Check engine light (CEL) is illuminated on your Corolla's instrument panel.
2. A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
   • OBD I -41: Throttle Position Sensor Circuit Malfunction.
   • OBD II -P0120: Throttle Position Sensor Circuit Malfunction.
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.

Where To Buy The Throttle Position Sensor And Save

Where can you buy the TP sensor for your 1.6L Toyota Corolla? You can buy it at your local auto parts store but it's gonna' cost a whole lot more. I suggest taking a look at the price of the TP sensor in the following links and compare:

Not sure if the above TP sensor fits your particular 1.6L Toyota? 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

As you probably already know, the TP sensor's job is to measure the angle of the throttle plate as you step on or release pressure on the accelerator pedal. The TPS translates the different throttle angle movements to a voltage signal.

This voltage signal increases as you press on the accelerator pedal(and the throttle plate opens) and decreases back to its original closed throttle plate voltage as you release pressure off of the accelerator pedal.

This very predictable voltage action makes it easy for you and I to use a multimeter and verify the TPS is actually doing this. If the voltage increases/decreases as the throttle plate opens/closes, then we can conclude the TPS is OK. If the throttle angle voltage does not increase/decrease as you open/close the throttle plate, then you can conclude the TPS has failed and needs to be replaced.

NOTE: Need a multimeter or need to upgrade the one you've got? This is the one that I use and recommend, and you can check it out here: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).

IMPORTANT: The TP sensor must remain connected to its 4-wire connector to check the TP signal voltage output. You'll need to either back-probe the connector or use a wire piercing probe on the wire. If you don't have such a tool, this is the one that I use and recommend: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

To verify this increase/decrease in the throttle angle voltage, this is what we need to do:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Connect the red multimeter test lead probe the middle wire of the sensor's connector.
   
   This is the wire that connects to TPS pin #3 in the illustration above.
   
   NOTE: The TP sensor must remain connected to its 4-wire connector.

3. 3

   Ground the black multimeter test lead on the battery negative (-) terminal.

4. 4

   Have your helper turn the key ON, but don't start the engine (this will power up the TP sensor).

5. 5

   Your multimeter should report a voltage between 0.2 to 0.9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.

Part 2

1. 6

   Now, slowly open the throttle (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.
   
   For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.

2. 7

   As the throttle opens, the voltage numbers will increase.
   
   This increase in voltage should be smooth and without any gaps or skips. Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.

3. 8

   Slowly close the throttle. As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 5.

Part 3

1. 9

   Lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle and observe the multimeter.
   
   If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.

2. 10

   Repeat step 9 several times to make sure of your multimeter test results.

Let's take a look at your test results:

CASE 1: The voltage increased/decreased as you manually opened/closed the throttle plate. This test result confirms that the TP sensor is OK and not defective.

CASE 2: The voltage DID NOT increase/decrease as you manually opened/closed the throttle plate. This tells you that the throttle position sensor (TPS) on your Corolla has a problem.

Before condemning the TPS to the scrap heap, you need to make sure that it's getting both power and Ground. To check for power, go to: TEST 2: Verifying Throttle Position Sensor Has 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: Verifying Throttle Position Sensor Has Power.

TEST 2: Verifying Throttle Position Sensor Has Power

If in TEST 1 the throttle position sensor DID NOT report an increasing/decreasing throttle angle voltage as you opened/closed the throttle plate, then we need to make sure that the TPS is being fed power and Ground before concluding the sensor has failed.

In this test step, we're gonna' make sure that the TPS is being fed power. This power is in the form of 5 Volts and are provided by your Corolla's fuel injection computer.

The wire that feeds this voltage to the TPS is the one that connects to terminal 4 of the TPS engine wiring harness connector (as identified in the illustration above).

OK, to get this test under way, these are the test steps:

1. 1

   Disconnect the TP sensor from its connector.

2. 2

   Place your multimeter's dial in Volts DC mode.

3. 3

   Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative (-) battery terminal.

4. 4

   Turn the key ON but don't start the engine.
   
   This will power up the TP sensor's connector.

5. 5

   Probe the TPS connector terminal that corresponds to pin #4, of the TPS connector, with the red multimeter test lead.
   
   IMPORTANT: Be careful when probing the metal female terminal of the TPS connector. Damaging the terminal will require that you replace the connector. Use a back probe or a wire piercing probe instead of probing the front of the connector.

6. 6

   Your multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:

Let's take a look at what your test results mean:

CASE 1: Your multimeter registered 4.5 to 5 Volts. So far so good since this tells you that the throttle position sensor (TPS) is getting power from the powertrain control module (PCM).

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: Verifying Throttle Position Sensor Has Ground.

CASE 2: Your multimeter DID NOT register 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: Verifying Throttle Position Sensor Has Ground

In this last test step, we're gonna' make sure that the throttle position sensor is being supplied with a good Ground.

This Ground is supplied by your Corolla's fuel injection computer. The wire that feeds the TPS with this Ground is the one that connects to terminal number 1 of the TPS engine wiring harness connector (see illustration above).

IMPORTANT: Be careful and do not accidentally or intentionally short this Ground circuit to battery voltage or you'll fry your Corolla's fuel injection computer.

These are the test steps:

1. 1

   Disconnect the TP sensor from its connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

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

4. 4

   Turn the key to its ON position but don't start the engine. This will power up the PCM.

5. 5

   Probe the TPS connector wire that connects to the TP sensor's pin #1 with the black multimeter test lead.
   
   Be careful not to damage the terminal if you probe it on the front of the connector.

6. 6

   Your multimeter will display 10 to 12 Volts if the BLK wire is feeding the TPS with Ground.

Let's interpret your test results:

CASE 1: The multimeter showed 10 to 12 Volts. This tells you that the throttle position sensor, on your Toyota, is being fed with Ground from the PCM.

All three test have confirmed that:

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

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).

After replacing the TPS you'll need to adjust it to the correct specification. To adjust the TPS, this tutorial's subheading ‘Adjusting The Throttle Position Sensor Assembly’ will help: TPS Idle Switch Multimeter Test (1.6L Toyota Corolla).

CASE 2: Multimeter DID NOT show 11 to 12 Volts. Double check that you're testing the correct TP sensor harness terminal wire and repeat the test.

If your multimeter still doesn't show the indicated voltage, then we can conclude that there's an open in the wire between the TP sensor harness connector and the PCM's harness connector. In the extreme of cases, the PCM has an internal problem (although this is very rare).

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 1.6L Toyota as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).

More 1.6L Toyota Corolla Diagnostic Tutorials

You can find a complete list of 1.6L Toyota Corolla diagnostic "how-to" tutorials in this index:

• 1.6L Toyota Corolla Index of Articles.

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

• How To Test The Ignition Coil (1996-1997 1.6L Toyota Corolla).
• How To Test The Fuel Pump (1993-1996 1.6L Toyota Corolla).
• How To Do A Cylinder Balance Test (1989-1997 1.6L Toyota Corolla).
• How To Test The Fuel Injectors (1993-1997 1.6L Toyota Corolla).