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How Do You Know if a Throttle Position Sensor is Bad

Updated on August 11, 2016
Throttle position sensor (right hand side device).
Throttle position sensor (right hand side device). | Source

Yes. How do you know if a throttle position sensor (TPS) is bad? Of course, some symptoms can tell you when a TPS may be bad. But these symptoms may come from other bad sensors, parts or components. So you need to conduct some tests.

The TPS connects to the throttle plate on the throttle body. The position sensor has a variable resistance potentiometer (or contact points, depending on model) that sends a varying voltage signal to the Power Control Module (PCM, your car's engine computer) according to the position of the throttle plate.

This plate rotates when you depress the gas pedal to allow more air to enter the intake manifold. With the engine running, the position of the throttle plate (along with other sensors) tells the computer how much fuel the engine needs at any given moment.

So, without the correct signal coming from the TPS, you begin to notice drivability problems. Fortunately, it's not that hard to test the sensor. You can use the position sensor operating characteristics to test it using a digital multimeter (DMM).

If you haven't used a multimeter before, just take a look at the next video. In a couple of minutes you'll be ready to test the throttle position sensor in your car. And if you're looking for an inexpensive but good DMM for your toolbox—you need to use one for many DIY car projects—you can find one at your local auto parts store or online.

The most typical failure you'll find on a TPS is wear, a short or an open on the circuit of the contacts or variable resistor. This guide will help you test the throttle position sensor in a few minutes and know whether you need to replace it.

Index

I. How to Test a Throttle Position Sensor

A. Is Your TPS Connected to Ground?

B. Is Your TPS Connected to Reference Voltage?

C. Is Your TPS Producing the Correct Signal Voltage?

WARNING - Using a DMM

II. Throttle Position Sensor Adjustment

Bad TPS Symptoms
Lean and Rich fuel condition problems
Bad computer signals to other actuators
Ignition timing problems
Triggering of trouble codes (depending on car model)
Rough idle
Hesitation
Stumble
Surging
Stalling
Crank-No start condition

I. How to Test a Throttle Position Sensor

The most common TPS test is to measure for resistance (ohms) or voltage at the various positions, including throttle plate closed, half open and fully open. We'll use voltage to test the TPS here.

1. Open the hood and remove the air cleaner assembly where it connects with the throttle body.

2. Inspect the throttle plate and the walls of the throttle body surrounding the throttle plate.

* If you see carbon buildup around the walls and under the throttle plate, spray some carburetor cleaner on a clean shop rag and wipe the buildup with it until the surface is completely clean. Carbon buildup can prevent the throttle plate from closing properly and moving freely.

3. Locate the TPS mounted on the side of the throttle body. The TPS is a small plastic block with a three wire connector.

Source

A. Is Your TPS Connected to Ground?

1. Carefully unplug the electrical connector from the TPS.

2. Examine the electrical connector wires and terminals for dirt, contamination and damage.

3. Now, set your DMM to a suitable setting, like 20 Volts, on the DC voltage scale.

4. Turn the ignition key to the ON position, but don't start the engine.

5. Connect the red test lead from your DMM to the battery positive post, the one marked with a "+" sign.

6. And touch the black test lead from your DMM to each of the three electrical terminals of the TPS electrical connector.

* The one terminal that reads 12 Volts on your DMM is the ground terminal. Make a note of the color of this wire.

* If none of the terminals reads 12 Volts, there's a problem in that part of the wiring leading to the TPS you need to fix because the TPS has no ground.

7. Turn the ignition key OFF.

Locate the TPS to the side of the throttle body.
Locate the TPS to the side of the throttle body. | Source

B. Is Your TPS Connected to Reference Voltage?

1. Now connect the black test lead from your DMM to the ground terminal on the TPS connector you just identified.

2. Turn the ignition key to the ON position, but don't start the engine.

3. Connect the red test lead to each of the other two terminals.

4. One of the terminals should read 5 volts, or pretty close to it. That terminal is providing the reference voltage to the TPS to produce the voltage signal. Make a note of the color of the wire connected to this terminal. The third wire corresponds to the signal voltage or signal wire.

* If you don't get 5 volts from any of the two terminals, there's a problem in the circuit you need to fix because there's no reference voltage going to the TPS. Check the circuit for bad terminals, loose, dirty or damage wires.

5. Turn the ignition key OFF.

6. Plug back in the electrical connector to the TPS.


C. Is Your TPS Producing the Correct Signal Voltage?

1. Now backprobe the signal and ground terminals on the TPS electrical connector. If necessary, use a couple of pins to backprobe the wires.

2. Connect the positive (red) test lead from your DMM to the signal wire and the black negative (black) test lead from your DMM to the ground wire.

3. Turn the ignition key ON but don't start the engine.

4. Make sure the throttle plate is fully closed.

5. Your DMM should read around 0.2 up to 1.5 Volts or close to it, depending on your particular model. If the readout on your meters shows only a zero, make sure you're at a low setting—usually at the 10 or 20 Volts setting. If your meter still reads zero, continue with this test anyway.

6. While watching the readout on your DMM, gradually open the throttle plate until is fully opened (or have an assistant gradually depress the gas pedal to the floor).

* Your DMM should read 5 volts or close to it when the throttle plate is fully opened.

* Also, make sure that the voltage increases smoothly as you gradually open the throttle plate.

* If you notice the voltage skipping or stuck at a certain voltage value, as you gradually open the throttle plate, your TPS is not working properly and you need to replace it.

* Also, if your TPS doesn't reach 5 volts, or close to it (up to 3.5V on some models), when the throttle plate is fully opened, replace the TPS.

7. Repeat step 21, only this time use the handle of a screwdriver to lightly tap on the position sensor as you open and close the throttle plate. If the voltage skips as you tap the sensor, replace it.

8. Turn OFF the ignition key and remove the pins.

If your have an adjustable throttle position sensor (old vehicle model), and your readings are out of specification, try to adjust the sensor first before replacing it. Your sensor is adjustable if you can loosen the sensor mounting bolts and rotate the sensor left or right. If necessary, head over to the next section Throttle Position Sensor Adjustment.

WARNING - Using a DMM

When testing electronic devices in your car, use a 10-megaohm impedance digital multimeter to protect sensitive electronic devices in your vehicle.

II. Throttle Position Sensor Adjustment

This is an example of an adjustment on an externally mounted TPS. Other models with different configurations require a variation of the following steps. But this will give you a general idea of the adjustment procedure.

1. Loosen the sensor mounting bolts just enough so that you can rotate it by lightly tapping on it with a screwdriver handle.

2. Backprobe the position sensor to monitor the voltage signal with your DMM.

3. Turn the ignition key to the ON position but don't start the engine.

4. Keep the throttle plate at the close position (or at the position specified in your repair or service manual).

5. Verify that the voltage corresponds to the specified in your manual. If not, rotate the sensor left or right until you obtain the specified voltage.

6. Then, hold the TPS in that position and tighten up the mounting screws.

If the TPS is unable to reach the specified voltage, replace it.

NOTE: On some models, you need a feeler gauge to adjust the position sensor. Also, you may need to adjust a stop screw in the throttle body and, still in some other models, adjust a dash pot that prevents the throttle plates from suddenly closing. For this, read the instructions in the repair manual for your specific vehicle make and model.

Knowing how to test a throttle position sensor can save you time, and, most importantly, prevent you from changing parts unnecessarily. So this simple test can help you get your car back on the road faster. And the test is not difficult. You can do it at home in just a few minutes.

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