How To Test the Throttle Position Sensor (TPS) -1998-2002 1.8L Toyota

The throttle position sensor (TPS) on your 1998-2002 1.8L equipped Toyota Corolla can be easily tested with just a multimeter.

Not only is this test fast and easy... but it's also a very accurate test and will let you know if the TPS is bad (or not).

By testing the throttle position sensor (TPS) with your multimeter, you'll also be able to diagnose any of the following TP sensor trouble codes that may be lighting up the check engine light (CEL) on your Toyota:

  1. P0120: Throttle Position Sensor (TPS) Circuit.
  2. P0121: Throttle Position (TP) Sensor Circuit/Range Performance.

Here are the contents of this tutorial at a glance:

  1. Basics of the Throttle Position Sensor (TPS).
  2. TEST 1: Checking the Throttle Position Sensor (TPS) Signal.
  3. TEST 2: Checking Throttle Position Sensor (TPS) Power.
  4. TEST 3: Checking Throttle Position Sensor (TPS) Ground.
  5. Where to Buy the TPS and Save.
  6. 1.8L Toyota Tutorials.

Basics of the Throttle Position Sensor (TPS)

How To Test the Throttle Position Sensor (TPS) -1998-2002 1.8L Toyota

The throttle position sensor's job is to measure the angle of the throttle plate as you step on (and step off) the accelerator pedal... since the throttle plate is connected to the accelerator pedal via the accelerator cable.

Your Toyota's PCM receives this throttle angle info on the middle wire. The other two provide power and ground (to the TPS).

In the table below, you'll find a short description of what each wire does:

1.8L Toyota Corolla TPS Circuits
(2001, 2002, 2003, 2004, 2005, 2006, 2007)
Pin Wire Color Description
1 YEL 5 Volts
2 BRN Sensor Ground
3 LT GRN Throttle Position Signal

TEST 1: Checking the Throttle Position Sensor (TPS) Signal

How To Test the Throttle Position Sensor (TPS) -1998-2002 1.8L Toyota

The throttle position sensor (TPS) sends the throttle plate angle voltage signal (it creates as the throttle plate opens and closes) on the LT GRN (light green) wire.

So, in this test section, you'll tap into this LT GRN wire and manually open and close the throttle plate to see if the TPS is creating an increasing/decreasing voltage signal.

If the TPS is bad on your Toyota Corolla... then the voltage output will stay stuck at one value no matter how much you open or close the throttle plate.

If the TPS is OK, then the voltage output of the sensor will increase/decrease as you manually open/close the throttle plate.

IMPORTANT: This is an on car test of the sensor and the throttle position sensor must remain connected to its harness connector.

Here are the test steps:

  1. 1

    Place your multimeter in Volts DC mode and connect the red test lead to the LT GRN wire of the TP sensor harness connector.

    NOTE: The TP sensor connector needs to be connected to the TPS, so you'll need to either back-probe the connector or use a wire piercing probe to get to the signal inside the wire (to see what a wire piercing probe looks like: Wire Piercing Probe Tool).

  2. 2

    Ground the black multimeter lead directly on the battery negative (-) post.

    At this point (with the throttle plate closed) your multimeter should read a voltage between 0.3 to 1.0 volt DC.

  3. 3

    Manually rotate the throttle.

    You'll get the best results by opening and closing the throttle directly on the throttle body instead of stepping on the accelerator pedal.

  4. 4

    The multimeter should show an increasing voltage as you (or your helper) open up the throttle.

    With the throttle plate completely open, your multimeter should read: 3.2 to 4.9 Volts DC.

    You'll get the best results by opening and closing the throttle directly on the throttle body instead of stepping on the accelerator pedal.

  5. 5

    The multimeter should show a decreasing voltage as you begin to close the throttle.

  6. 6

    Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle and observer the multimeter.

    The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gap's in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screw-driver's handle.

CASE 1: The TP sensor signal's voltage increased and decreased smoothly and without gaps. This tells you that the TPS on your Toyota Corolla is working and not defective.

This test result also tells you that:

  1. Circuit #1 is providing power.
  2. Circuit #2 is providing ground.

CASE 2: The TP sensor signal's voltage did not increase or decrease. In the majority of the cases this TPS result tells you that the sensor is bad. But not always.

To be sure that the TPS is truly fried, we need to do 2 more tests. These tests involve checking that the sensor is getting both power and ground. For the first of these two tests, go to TEST 2: Checking Throttle Position Sensor (TPS) Power.

CASE 3: The TP sensor signal's voltage showed gaps in its voltage output as you tapped the sensor with the screwdriver. If the gaps in the multimeter's voltage readings only showed up when you were tapping on the TPS (with the screwdriver's handle) then this test result tells you that the TPS is bad and needs to be replaced.