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How Do You Know if a Throttle Position Sensor Is Bad?

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Throttle position sensor (right hand side device).

Throttle position sensor (right hand side device).

Is Your Throttle Position Sensor Bad?

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.

On some vehicle models with an automatic transmission, a bad TPS can interfere with kickdown shifts and downshifts.

So, without the correct signal coming from the TPS, you begin to notice drivability problems. Some vehicle models provide a "limp-in" mode to allow the driver to take in the vehicle to a shop for diagnostics and repair. 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

III. Common TPS Diagnostic Trouble Codes

Bad TPS Symptoms

Lean and Rich fuel condition problems

Car only reaches a low, limited speed (lack of power)

Bad computer signals to other actuators

Gear shifting issues (automatic transmission)

Ignition timing problems

Triggering of trouble codes (depending on car model)

Rough idle

High idle speed

Hesitation

Stumble

Surging

Stalling

Crank-No start condition

Engine starts then stops

Increase in fuel consumption

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.

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.

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 6, 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.

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.

III. Common TPS Diagnositc Trouble Codes (DTCs)

A fault in the TP sensor or circuit may trigger the check engine light. These are three typical codes and their probable cause you may find stored in your car's computer memory.

DTCDescriptionPotential Fault

P0121

TPS signal disagrees with MAP signal

Faulty vehicle speed sensor signal

 

 

Bad TP sensor.

 

 

Faulty MAP sensor.

P0122

TPS low voltage

Internal short to ground.

 

 

Sensor or circuit open.

 

 

Sensor or circuit shorted to ground.

P0123

TPS high voltage

Circuit shorted to voltage.

 

 

Sensor shorted to 5V reference voltage.

 

 

Sensor ground open.

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.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: If I throttle my car, it takes too long to decrease the acceleration. Is it from the TP sensor? The check engine light is also on.

Answer: Not necessarily. Pull down the codes and see what the computer is pointing at as the fault. There might be another sensor not responding quite right.

Question: What does it mean if my throttle goes straight to 5v before you move the throttle?

Answer: The resistance is probably bad.

Question: TPS light came on. I put a new the throttle body did relearn, light went out. I drove and the light is back on. I checked the codes and got TPS error. I did another relearn. Then no acceleration. I changed gas pedal (TPS) light went out. Drove and light is back on. Code reads bad TPS. A bad part? Returned it and installed. Still no acceleration. I'm about to pull my hair out. Wiring issue maybe? Any suggestions?

Answer: The problem might be in the circuit or the harness connector. Tug at wires and make sure they are properly connected. Check the connector for corrosion or build up. You may need to trace voltage in the circuit. Use the wiring diagram in the repair manual. There could also be a problem with the driver on the computer, but this is rarer.

Question: What does it mean if your car can’t pass 2500 rpm?

Answer: It is most likely a fuel system problem. It can be either a clogged fuel filter or blocked exhaust system (possibly the cat).

Question: I got a reference voltage of 5 V, and the initial voltage was .59 V. The highest reading was 3.73 V. Voltage goes up and down with no fluctuations. The car is a Jeep Commander with 4.7 V8. Can you tell me if the values I gave is OK?

Answer: The highest reading seems kind of low. You should check the specs in your repair manual. If you don't have the manual, your local library might have a copy. Make sure the voltage increases smoothly. Any small jumps are signs for concerned.

Question: What if the throttle is reaching above 5 volts?

Answer: The reference signal is usually about 5 volts - check the specs for your particular model, if it is too high. If you don't have the manual, your local library probably has a copy.

Question: I have an 03, Z71. The TPS and throttle body are one piece. Codes read the TPS was bad, so I replaced the throttle body. Codes still say throttle body is bad. Do you have any thoughts?

Answer: You need to check the reference signal to the sensor and what the sensor is reporting to the computer. It could be a problem in the circuit or the connector. You can use a DMM for this. Use your vehicle repair manual to check or identify the wires, if necessary.

Question: My VW Touran has a 4-pin connector, and I was stumped at the first hurdle as all pins seemed to be grounded and showed 12 volts. Could this mean a relay or perhaps fuse has gone?

Answer: Check first the fuse and/or relay -- you may need the electrical diagram if there's a short somewhere in the circuit. If you don't have the vehicle repair manual for your model, your local library may have a copy.

Question: My Toyota Premio with a D-4 engine. It shows up the engine check light after driving a distance of about 4km after starting the engine. Once the engine check light shows up, the acceleration power decreases, and I am forced to press the accelerator pedal harder for the engine to respond (and this is resulting in high fuel consumption). What could be causing this and how can I solve this problem?

Answer: You may try a temporary fix. Try turn the ignition Off and then On again. See if this helps. Still, you need to scan your car’s computer for trouble codes and fix the issue according to the diagnostic.

Question: My throttle opens when I turn the car on, then closes after a few seconds while the car is still on. Then, the car won't start. What could be the problem?

Answer: Check the idle air control (IAC) solenoid. If the solenoid doesn’t respond properly, you’ll have this type of issue. If possible, remove the IAC and connect direct battery voltage to the solenoid and see if it works properly. Also, check for carbon buildup in the sensor itself and the throttle ports where it mounts.

Question: I own a 2012 Suzuki Eeco minivan. For the last few months, my van won't start when hot or after running the A/C in idle for a few minutes. What could be the problem?

Answer: It's possible your alternator is getting "weak". But also have the battery checked. This other post might help as well, especially the third section.

https://axleaddict.com/auto-repair/Why-is-My-Car-H...

Question: I have an 08 Impala. The throttle plate doesn't close completely. It starts at .70. Why doesn't it close? Does it need to be relearned?

Answer: The opening is normal it helps the engine breath when your foot is off the gas.

Question: I have a1999 C230 Kompressor. All signs point to a bad throttle position sensor, but it never comes up in the fault codes. My question is, why is not coming up in the trouble codes?

Answer: A failed throttle position sensor, or other sensor for that matter, that hasn’t failed with the voltage parameters expected by the computer to know it has failed, won’t set a trouble code. For example, no voltage signal, a stuck voltage, etc. This may vary by model and the computer won’t registered a bad sensor until it fails a few times. Regardless, make sure to troubleshoot the TPS to make sure it has failed. The problem could be in the circuit as well.

Question: I think my TPS is bad, or possibly the throttle body itself. I was about to do this test per your directions, but my son insists that it can not be the TPS because no warning light came on the dash. Do you know if it could be bad, and still not display dash light, and if there is no dash light, would it still possibly throw a code? Thanks so much for your time.

Answer: Ideally, a faulty TPS would throw a code. But the computer has to follow the enable criteria to do this. It is possible for a TPS to become faulty and not throw a code. The TPS may develop dead spots that the computer is not catching if other conditions are not set. It's better to test it and operate the TPS manually slowly and carefully check the readout. Changes should be smooth.

Question: According to the scanner, there's a problem with the throttle of my Toyota Avanza 1.5. Every time I accelerate it won't accelerate and turn off in his own. What should we do to fix it? But sometimes the car works properly.

Answer: Check the connector and the TPS. The resistance or wiper arm inside may be failing. Check that voltage changes smoothly. A jumpy reading will tell you the sensor is failing.

Question: My TPS has been replaced twice in ten days. What could cause this?

Answer: Have the TPS circuit checked. Compare voltages to specs. Start with a visual inspection of the wires and connector. Look for wire damage and loose wires at the connector.

Question: Can the TPS sensor affect shifting of gear up?

Answer: On some models, it can lead to shifting problems. Test the TPS sensor. You may need your vehicle repair manual for this. I hope it helps. Also, download trouble codes, even if the engine light is not on. There could be pending codes.

Question: My throttle position sensor is not getting ground. What do I do?

Answer: Check along the wire, from the sensor to the computer, that provides ground to the sensor. Make sure the wire is not damaged, or loose in the harness. Use a test light. If the wire is OK, the problem could be on the computer itself. In this case, it is better to fix the ground on the computer. Trying to run a new ground to the sensor may create other issues.

Question: What is the initial voltage for a throttle position sensor?

Answer: You should get a voltage at the lower end. It could be less than 1 or around 1 volts, depending on your model.

Question: I have a 2012 Silverado. The TPS came back with "Check Engine" during a code test. Do I need to replace just the sensor or the entire throttle body?

Answer: TPS code wording usually changes from one manufacturer to the other. It is better to test the sensor first if possible, especially if you only got one trouble code. You may need your vehicle repair manual to test the sensor and a digital multimeter. You may find the TPS or electronic throttle body at fault.

Question: 2008 Toyota Tacoma. It starts normal but will not continue to run. If I pump the gas pedal, I can keep it running between 3-4000 rpm. Would the TPS sensor cause this?

Answer: The problem could be in the fuel system. Check the fuel injectors and fuel pressure regulator foe leaks.

Question: My Ford Freestyle began cutting off at stops and looses power when the security light comes on. What could be the problem?

Answer: If your vehicle uses a smart key or smart key fob, check the battery; it may be dying or there could be a faulty chip. Another possibility is a a problem with the anti-theft module or the wiring to the module.

Question: In the 'connected to ground' test I have two that read about 12v. Assuming black is ground, I also get 'reference' voltage readings close to 5 for the other two wires. Is one of the wires shorted out?

Answer: You should get around 5 volts for the reference wire. The other is the signal wire. If you are getting 5v as well there could be a problem with the control circuit.

Question: The TPS has 2 wires not 3 wires, why?

Answer: I believe you have an idle or WOT switch. On some models, this is actually an idle switch (manual transmission) or wide-open throttle switch (automatic transmission). Instead of a 5-volt reference, it works with a 12v reference.

Question: Why can't my EOBD1 reader connect?

Answer: Check the user's manual. This could be a communications error. Make sure it is appropriate for your application. If necessary, you may want to contact the manufacturer.

Question: Got a 2004 Volvo S60 T5. There's literally no throttle response when depressing the accelerator pedal? I'm told it's the TPS sensor/module?

Answer: The problem could be with the module, the electrical connectors (module or pedal) or position transmitter. Check for trouble codes, even if the check engine light is not on. There could be a pending code to guide in the diagnostic.

Question: Hi. I have a 2008 Ford Focus, 1.4L. The EML and red cog on dash indicate throttle positioning sensor. I have changed the throttle body and the entire accelerator pedal (sensor included) and the issue is still there. The car will drive perfectly normal until the red cog light appears on the dashboard. There is then a loss of power and there is a delay between pushing the accelerator and the car accelerating. What could be the problem? Please help!

Answer: The red cog usually comes on because of a fault with the glow plugs or the relay. But it's better to have it diagnosed. There could also be a problem in the powertrain.

Question: I'm trying to test my throttle position sensor on my 2006 Dodge Dakota 3.7 V6. The wire harness for my TPS has 6 wires. How do I test it?

Answer: You need to identify the wires first (signal, ground, and reference). You may need the vehicle repair manual for this. It'll help you id the wires and walk you through the test.

Question: I have a 2011 Dodge Caliber. The lighting bolt and check engine light goes off for awhile, then will come back on. I have changed the throttle body, gas pedal and sensor. What else could be wrong with it?

Answer: Probably the computer needs to be reset after the repair you made. Check your vehicle repair manual. You'll probably find how to reset it yourself. Also, check for other trouble codes stored in memory that can guide you here, if necessary.

Question: A/C stopped working. We replaced the blower and resistor. Now the CE light code reads TPS. Is it possible the sensor was tripped by the removal for the gas pedal? Or is this a whole new issue? If we have the code reset and the CE light doesn't come back on, does that indicate that is was tripped by doing the previous work? Also if it does come back on after resetting, does it mean it is bad?

Answer: It is possible if the computer didn't receive an expected input from the sensor. Test the TPS using a digital multimeter. Make sure that it's still working and, if necessary, visually inspect and test the wires and connector. If the sensor tests OK, erase the code. If it comes back or you notice a performance issue. Take a closer look at the circuit or sensor. Hope this helps.

Question: The wire showing 5 volts is ground? Shouldn't that be your hot? Meanwhile, a continuity test will show ground, not voltage?

Answer: The 5 volts is your reference voltage. You also get close to 5 volts with the throttle full opened. Check the specs for your particular make and model, if necessary.

Question: My 2006 Mercury Mariner jerks and feels like it wants to stall when I accelerate. I've cleaned out the EGR valve, EGR vacuum; cleaned out the throttle body and checked my vacuum hoses for clogs. Still jerking. I'm out of ideas. Any ideas?

Answer: This could be a faulty throttle position sensor, a fault in the ignition fuel system or a vacuum leak. Check for diagnostic trouble codes, even if you check engine light is not on. There could be a bad sensor. This other post may help:

https://axleaddict.com/auto-repair/Why-My-Engine-H...

Question: My 2009 Volkswagen Tiguan is throwing a Throttle Actuator Control Range\Performance code. Will this keep car from cranking? I want to be sure before I change anything.

Answer: It is possible that you can have a hard time starting the engine or starting the engine at all. Often the symptoms are performance, driveability issues, hesitation, stumbling, and others.

Be aware that this type of failure can point to a problem with the controller area network (aka CAN): a sort of communication mediator between modules. You may need a professional scanner to be more precise about the cause for the trouble code (P0638).

There could be problems with the throttle actuator, its position switch, a circuit problem in one of the modules are some of the other reasons for this code.

So make sure this is the only code in the computer’s memory. You may want to have a shop scan the computer first before making any decision.

© 2016 Dan Ferrell