In this tutorial I'm gonna' show you how to test the throttle position sensor (TPS) on the 1995-1998 1.5L Mazda Protege.
The test is done with a multimeter, no scan tool required! All of the test steps are explained in a step-by-step manner.
In 3 tests you will be able to easily diagnose the throttle position sensor as bad (or not).
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1995-1998 1.5L Mazda Protege) (at: autotecnico-online.com).
APPLIES TO: This tutorial on testing the TPS applies to the following vehicles:
- 1.5L Mazda Protege: 1995, 1996, 1997, 1998.
RELATED TROUBLE CODES:
- P0122 -What Does It Mean? (1996-1998 1.5L Mazda Protege).
- P0123 -What Does It Mean? (1996-1998 1.5L Mazda Protege).
Symptoms Of A Bad Throttle Position Sensor
It's the throttle position sensor's job to measure the throttle plate angle as it opens or closes as you step on or off the accelerator pedal.
In a nutshell, the throttle position sensor produces a voltage signal that increases as you step on the accelerator pedal and the throttle plate opens.
As you step off the accelerator pedal, the throttle plate starts to close and the TPS voltage signal decreases back to its original base voltage.
All of these throttle plate angle changes are constantly reported to the fuel injection computer on your 1.5L Mazda Protege.
Since the throttle position sensor (TPS) is such an important component of the engine management system, when it fails you're gonna' definitely feel the engine resent it.
You're going to see the following TPS diagnostic trouble code lighting up the check engine light:
- P0121 Throttle Position Sensor Performance Problem.
- P0122 TPS Voltage Too Low.
- P0123 TPS Voltage Too High.
You're also going to see one or more of the following symptoms:
- Won't pass the emissions test.
- Bad gas mileage.
- Lack of power, rough idle, or hesitation.
- Engine cranks a long time before starting.
Throttle Position Sensor (TPS) Circuit Descriptions
Below are the circuit descriptions of the 3 wires of the throttle position sensor's connector.
| Terminal | Wire | Description |
|---|---|---|
| 1 | Light Green With Red Stripe (LT GRN/RED) | 5 Volts |
| 2 | Light Blue With Yellow Stripe (LT BLU/YEL) | TPS Signal |
| 3 | Black With Red Stripe (BLK/RED) | Ground |
Where To Buy The TPS And Save
The following links will help you to comparison shop for the throttle position sensor on your 1.5L Mazda Protege:
NOTE: The above throttle position sensor (TPS) fits the following vehicles: 1995, 1996, 1997, 1998 1.5L Mazda Protege.
TEST 1: Testing The TPS Voltage Signal
For our very first test, we're gonna' make sure that the throttle position sensor is creating a voltage signal that increases/decreases as you open/close the throttle plate.
We're going to connect multimeter to the blue with yellow stripe (BLU/YEL) wire of the sensor's 3-wire connector.
The BLU/YEL wire is one that carries the TPS voltage signal to your Mazda Protege's fuel injection computer.
In the photo above, I have labeled the BLU/YEL wire with the number 2.
If the throttle position sensor is bad, you'll see that the TPS voltage signal stays stuck in one value as you open/close the throttle plate.
IMPORTANT: The throttle position sensor (TPS) must remain connected to its electrical connector for this test to function properly. To be able to access the voltage inside the signal wire, you'll need to use either a back probe or a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe (easyautodiagnostics.com).
Let's get started:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the blue with yellow stripe (BLU/YEL) wire of the TP sensor harness connector.
The BLU/YEL wire is identified with the number 2 in the photo above. - 3
Ground the black multimeter test lead directly on the battery negative (-) post.
- 4
Manually rotate the throttle plate.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 5
The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 6
The multimeter should show a decreasing voltage as you begin to close the throttle plate.
- 7
Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.
The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps 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.
Let's analyze your test results:
CASE 1: The TPS voltage signal increased/decreased as you opened/closed the throttle plate. This is the correct test result and it indicates that the throttle position sensor is good.
With this test result you can also conclude that the TPS sensor is getting both power (5 Volts) and Ground from the fuel injection computer.
CASE 2: The TPS voltage signal DID NOT increase/decrease as you opened and closed the throttle plate. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the LT GRN/RED wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Has 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the LT GRN/RED wire is feeding the TPS with 5 Volts. For this test go to: TEST 2: Making Sure The TPS Has 5 Volts.
