When an electrical component within your fuel injection system is bad, of course, you expect your engine to perform poorly.
In the long run, without dealing with these problems, your engine suffers, gradually gets damaged, and may stop working altogether.
The throttle position sensor is one of these components.
However, symptoms of a bad TPS usually coincide with symptoms of other faulty electrical components, and not a lot of people know how to diagnose it for issues.
This guide explains all you need to know about checking a throttle position sensor, including what it does for the engine and how to do a quick multimeter test.
Let’s get right in.
What Is A Throttle Position Sensor?
A throttle position sensor (TPS) is an electrical component within your vehicle’s fuel management system that monitors the intake of air into the engine.
It is mounted on the throttle body, directly monitors the position of the throttle plate, and sends signals to the fuel injection system to ensure that the right mixture of air and fuel is delivered to the engine.
If the TPS is bad, you experience certain symptoms like ignition timing problems, increased fuel consumption, and rough engine idling, amongst a barrage of others.
A multimeter is a great tool you need to test electrical components in your car and will come in handy if you experience any of these.
Now let’s see how to diagnose a throttle position sensor?
How To Test Throttle Position Sensor With Multimeter
Set your multimeter to the 10 DC voltage range, place the black negative probe on the ground terminal of the TPS, and place the red positive probe on the reference voltage terminal of the TPS. If the meter does not read 5 volts, the TPS is bad.
This is only one test out of the series of tests you carry out on the throttle position sensor and we will get into details now.
- Clean The Throttle
Before diving into your throttle position sensor with a multimeter, you have to take some preliminary steps.
One of these is to clean your throttle, as it could be the debris on it that prevents it from opening or closing properly.
Disconnect the air cleaner assembler from the throttle position sensor and check the throttle plate and walls for any carbon buildup.
Dampen a rag with a carburetor cleaner and wipe away any debris where you see a build-up of it.
Once you have done this, ensure the throttle fully opens and closes properly.
It’s time to move to the throttle position sensor.
This is a small plastic device located on the side of the throttle body and to which three different wires are connected.
These wires or connector tabs are important for our tests.
If you’re having trouble finding the wires, see our guide on how to trace wires.
Check the TPS wires and terminals for damage and a build-up of dirt. Take care of any impurities and proceed to the next step.
- Locate The Throttle Position Sensor Grounding
Finding the throttle position grounding determines if you have a problem and also helps with subsequent tests.
Set your multimeter to the 20 DC voltage range, turn your ignition to the “on” position without starting the engine, and then place the red positive probe on the positive car battery post (tagged “+”).
Now, place the black negative probe on each of the TPS wire tabs or terminals.
You do this until one shows you a reading of 12 volts. This is your ground terminal and your TPS has passed this test.
If none of the tabs presents you with a 12-volt reading, then your TPS isn’t grounded properly and may need to be fixed or changed entirely.
If it is grounded, mark the ground tab and move to the next step.
- Find The Reference Voltage Terminal
With your car ignition still in the “on” position and the multimeter set to the 10 DC voltage range, place the black lead on the ground TPS terminal and place the red lead on each of the other two terminals.
The terminal that presents you with about 5 volts is the reference voltage terminal.
If you don’t get any 5-volt reading, then there is a problem within your TPS circuit and you may check for loose or corroded wiring.
On the other hand, if the multimeter displays an appropriate reading, then there is appropriate reference voltage being supplied to your TPS signal terminal.
The signal terminal is the third terminal that hasn’t been tested.
Connect the wires back into the throttle position sensors and move to the next step.
- Test The TPS Signal Voltage
The signal voltage test is the ultimate test that determines if your throttle position sensor is functioning properly or not.
It helps to diagnose whether the TPS accurately reads the throttle plate when it is fully open, halfway open, or closed.
Set the multimeter to the 10 DC voltage range, place the black probe on the ground TPS terminal, and place the red probe on the signal voltage terminal.
It may be difficult placing the multimeter leads on the terminals as the TPS is already reconnected to the throttle.
In this case, you use pins to back probe the wires (poke each TPS wire with a pin) and attach your multimeter probes to these pins (preferably using alligator clips).
With the throttle plate fully closed, the multimeter is expected to read between 0.2V to 1.5V if the throttle position sensor is in good condition.
The value displayed depends on the model of your TPS.
If the multimeter shows a reading of zero (0), you may still proceed to the next steps.
Gradually open the throttle plate and watch how the readings on the multimeter change.
Your multimeter is expected to display a steadily increasing value as you open up the throttle.
When the plate is fully open, the multimeter is also expected to display 5 volts (or 3.5 volts in some TPS models).
The TPS is not in good condition and needs to be changed if you experience the following:
- If the value massively skips while opening the plate.
- If the value gets stuck at a number for a long period.
- If the value doesn’t reach 5 volts when the throttle plate is fully opened
- If the value inappropriately skips or changes when you lightly tap the sensor with a screwdriver
All these are representations of a TPS that needs to be replaced.
However, if your throttle position sensor is an adjustable model, like those found in older vehicles, then there is more to do before deciding to replace the sensor.
Directions For Adjustable Throttle Position Sensor
Adjustable throttle position sensors are the types that you may loosen and configure by twisting them left or right.
If your adjustable TPS shows any of the signs mentioned above, you may want to reconfigure it before deciding to replace it.
The first step in this is to loosen the mounting bolts that attach it to the body of the throttle.
Once this is done, you back probe the terminals, as the TPS is still connected to the throttle.
Connect the negative multimeter lead to the ground TPS terminal and connect the positive lead to the signal terminal.
With the ignition placed in the “on” position and the throttle plate closed, turn the TPS left or right till you get the appropriate reading for your TPS model.
When you get the appropriate reading, simply keep the TPS in that position and tighten the mounting bolts on it.
If the TPS still doesn’t produce an appropriate reading, it is bad and you need to change it.
Here is a video on how you may adjust a throttle position sensor.
This process varies by the adjustable TPS model you use, and some may additionally require a feeler gauge or dashpot to get adjusted.
OBD Scanner Codes For Throttle Position Sensor
Obtaining OBD scanner codes from your engine is one of the easiest ways to find problems with your throttle position sensor.
Here are three diagnostic trouble codes (DTCs) to take note of.
- PO121: Represents when the TPS signal disagrees with the manifold absolute pressure (MAP) sensor, and could be caused by a bad TPS sensor.
- PO122: Represents low TPS voltage, and could be caused by your TPS sensor terminal being open or shorted to the ground terminal.
- PO123: Represents high voltage, and could be caused by a bad sensor grounding or the sensor terminal shorted to the reference voltage terminal.
That is all you need to know about testing your throttle position sensor.
As seen through the steps, the model or type of TPS you use determines what to check for and how these processes play out.
Although the tests are simple, refer to a professional mechanic if you bump into some trouble.
Frequently Asked Questions
How Many Volts Should A TPS Have?
A throttle position sensor is expected to have a volt reading of 5V when the throttle plate is closed, and a reading of 0.2V to 1.5V when the throttle plate is open.
What Does A Bad Throttle Position Sensor Do?
Some symptoms of a bad TPS include limited car speed, bad computer signals, ignition timing issues, gear shifting problems, rough idling, and increased fuel consumption, among others.
What Are The 3 Wires In Throttle Positioning Sensor?
The three wires in the throttle position sensor are the ground wire, the reference voltage wire, and the sensor wire. The sensor wire is the main component that sends the appropriate signal to the fuel injection system.
Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.