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).
The contents of this tutorial at a glance:
- Symptoms Of A Bad Throttle Position Sensor.
- TEST 1: Testing The Throttle Position Sensor Voltage Signal.
- TEST 2: Verifying Throttle Position Sensor Has Power.
- TEST 3: Verifying Throttle Position Sensor Has Ground.
- Where To Buy Your Throttle Position Sensor And Save.
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:
- Check engine light (CEL) is illuminated on your Corolla's instrument panel.
- 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.
- 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.
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.
To verify this increase/decrease in the throttle angle voltage, this is what we need to do:
Place your multimeter in Volts DC mode and with the red multimeter lead probe the middle wire of the sensor's connector. This is the wire that connects to TPS pin #3 in the illustration above.
Ground the BLACK multimeter test lead on the battery negative terminal. Have you helper turn the Key On, but don't start the engine (this will power up the TP sensor).
Your multimeter should report a voltage between .2 to .9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
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.
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.
Now, 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 4.
OK, now you'll need someone to help you 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.
Repeat step 7 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: 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.