In this tutorial, I'm going to show you how to test the throttle position sensor (TPS) on the 1995-1996 1.5L Toyota Tercel.
The really awesome thing about the TPS test, is that it can easily and accurately be done with just a multimeter. That's right, you don't need any expensive diagnostic equipment to perform the TPS test.
In this tutorial I'll explain how to diagnose it in 3 simple tests. With your test results, you'll be able to find out if it's bad or not.
You'll also be able to diagnose the following trouble codes: P0121: Throttle Position Sensor Circuit Range/Performance Problem.
Contents of this tutorial:
IDLE SWITCH TEST: If you need to test the idle switch part of the TPS, this tutorial will help: TPS Idle Switch Multimeter Test (1995-1996 1.5L Toyota Tercel).
Symptoms Of A Bad Throttle Position Sensor
The throttle position sensor's job is to measure the angle of the throttle plate in the throttle body.
As you're probably already aware, the throttle plate is connected to the accelerator pedal via an accelerator cable.
When you step on the accelerator pedal, the throttle plate opens to let more air into the engine. When you release the accelerator pedal, the throttle plate closes and less air enters engine.
The fuel injection computer needs to know how much the throttle plate opens or closes and it's the throttle position sensor's job to do so.
Since the throttle position sensor is such a critical component of the fuel injection system, when it fails, your 1.5L Toyota Tercel engine performance is going to suffer.
You're going to see one or more of the following symptoms:
- Check engine light (CEL) is illuminated on your Tercel's instrument panel.
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- P0120: Throttle Position Sensor Circuit Malfunction.
- P0121: Throttle Position Sensor Circuit Range/Performance Problem.
- Bad gas mileage.
- Hard start and/or extended cranking time (after shut off).
- Black smoke coming out of the tailpipe.
- Hesitation when accelerating your vehicle down the road.
Circuit Descriptions Of The TPS
Unlike the majority of the throttle position sensors, the TPS on your 1995-1996 1.5L Toyota Tercel has 4-wires coming out of its connector.
This is due to the fact that the TPS is two sensors in one. To be a bit more specific, the throttle position sensor assembly, on your 1.5 Toyota Tercel, is a combination of the TPS and an idle switch.
Although in this tutorial we're only going to be concentrating on testing the TPS part of the assembly, the following table has a description of all four wires:
| TPS Sensor Connector | ||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | Brown (BRN) | Ground |
| 2 | Yellow with black stripe (YEL/BLK) | Idle Switch |
| 3 | Yellow with green stripe (YEL/GRN) | TPS Signal |
| 4 | Light green with red stripe (LT GRN/RED) | 5 Volts |
To successfully diagnose the throttle position sensor (TPS), it's important to know that the TPS creates a voltage signal that increases as the throttle plate opens.
When the throttle plate is closed, the throttle position sensor create a TPS voltage signal of about 0.5 to 0.9 Volts DC.
As the throttle plate starts to open, like when you step on the accelerator pedal, this voltage value starts to increase.
When a throttle position sensor fails, you'll usually see that the TPS voltage signal stays stuck in one value no matter the angle of the throttle plate.
Where To Buy Your TP Sensor And Save
Where can you buy the TP sensor for your 1.5L Toyota Tercel? 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 1.5L Toyota Tercel? 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
To find out if the throttle position sensor is defective (or not), we're going to connect a multimeter to the yellow with green stripe (YEL/GRN) wire of the TPS 4-wire connector.
Then, we're going to manually open and close the throttle plate as we observe the voltage signal with our multimeter.
If the throttle position sensor is OK (not defective), then we should see the voltage signal increase as we open the throttle plate and decrease as we close it.
If the throttle position sensor is bad, on your 1995-1996 1.5L Toyota Tercel, then you'll notice that the TPS voltage signal will stay stuck at one value as you open/close the throttle plate.
IMPORTANT: The throttle position sensor must remain connected to its 4-wire connector for this test to function. You'll need to use a back probe or a wire piercing probe to read the TPS signal within the wires. You can see an example of this tool here: Wire Piercing Probe.
Let's get started:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red test lead to the YEL/GRN wire of the TP sensor's connector.
- 3
Ground the black multimeter lead directly on the battery negative (-) post.
- 4
Manually open 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.
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 examine 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 Tercel, has a problem.
Before condemning the TPS as bad, you need to make sure that it's getting both 5 Volts and Ground. For the next test, go to: TEST 2: Making Sure The TPS Has 5 Volts.
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 5 Volts or Ground. So the next step is to check that the TP sensor is getting 5 Volts, go to: TEST 2: Making Sure The TPS Has 5 Volts.