GMC Bad Throttle Position Sensor Symptoms


Modern vehicles are equipped with all manner of different sensors to assist with driving. When all of these sensors are working well, you won’t even notice it, but if even one of the more obscure sensors stops working, odds are it’ll result in some pretty obvious symptoms.

You might not think about your throttle position sensor very often, but if yours happens to fail then your driving experience will be noticeably affected. Such a failure can result in symptoms like weak or erratic acceleration, worse fuel economy, and rough idling, among others.

In this article, we’ll be going over the purpose and function of the throttle position sensor, and we’ll be covering the symptoms of a bad throttle position sensor in detail. We’ll also cover how to locate and replace the throttle position in your GMC vehicle.

What Is a Throttle Position Sensor, and What Does It Do?

The throttle position sensor is located on the throttle body and is used to measure how open the throttle valve is and how long it is open for. This is important because it helps the ECU (engine control unit) adjust the amount of fuel being sent to the cylinders, ensuring that the correct air/fuel ratio is entering the combustion chambers at all times.

The throttle position sensor is a part of your car’s greater fuel management system, and works in conjunction with a variety of other sensors and modules to help determine what the correct air/fuel ratio should be at at any given point. 

However, the position of the throttle is by far the most important factor when determining the right amount of fuel to deliver, so the throttle position sensor is one of the most critical sensors of your whole fuel management system.

Without a working throttle position sensor, your ECU would be unable to deliver the correct amount of fuel and also be unable to adjust the ignition timing for the situation. As we’ll discuss in the next section, this can present a pretty serious safety risk, not only for you but for other drivers on the road with you.  

Engine control unit (ECU)

Read: Bad Fuel Pressure Sensor Symptoms

What Are the Symptoms of a Bad Throttle Position Sensor?

Since a bad throttle position sensor is ultimately going to affect the amount of fuel that gets sent to the engine, you’re mostly going to see symptoms related to engine speed and fuel economy. Here’s what you should keep an eye out for if you think your throttle position sensor might be failing:

Rough Idle

An engine at idle will be spinning at roughly between 600 and 900 rpm. If your engine is at idle but you notice that your engine speed is significantly higher or lower than this, or if your engine speed keeps changing even when you’re not pressing the gas pedal, it’s possible that your throttle position sensor has failed. 

This happens because the malfunctioning sensor tricks the ECU into thinking that the throttle isn’t fully closed when it actually is. 

Read: What Happens if TPS Is Not Calibrated?

Weak or Erratic Acceleration

A failed throttle position sensor can have a significant effect on how your car accelerates when you hit the gas pedal. However, the nature of this effect can depend on how exactly the sensor has failed.

If the sensor has failed in such a way that the ECU thinks the throttle is still closed, the result will be that your car accelerates much more slowly than it normally does. Alternatively, it may accelerate normally for a brief period then suddenly lose all power, or it may accelerate roughly with lots of jerking and hesitation.

On the other hand, the sensor might fail in a way that causes the ECU to think the throttle is open when it isn’t. In this instance, you’ll find that your car suddenly accelerates even when you’re not actually pressing the gas pedal. 

Poor Fuel Economy

If a bad throttle position sensor is causing your engine to run rich all the time, you’ll find that your car’s fuel economy will suffer as a result. Obviously, an engine that runs rich will be burning way more fuel than it actually needs, so take note if you find that you’re all of a sudden having to fill up your car more often than normal.

Aside from draining your fuel faster, an engine that is running rich will give off a strong smell of gasoline, especially when you’re at idle. Regardless of the cause, however, if you find that your engine is running rich you should address the issue as soon as you can.

Check Engine Light Is On

If you notice that your check engine light is on after experiencing any of the above symptoms, this is a pretty clear indicator that something is wrong with your fuel management system. It doesn’t necessarily mean that the throttle position sensor is for sure the culprit, but there’s certainly a good chance that it is.

If your check engine light is on, that means your ECU has logged an error code. You can check the error codes logged in your ECU yourself as long as you have an OBD2 scanner. If you do have such a scanner and you want to check your ECU for error codes, these are some of the ones you should keep your eye out for:

  • P0121
  • P0122
  • P0123
  • P0124
  • P2135
  • P2138

Why Do Throttle Position Sensors Fail?

Throttle position sensors can sometimes wear out on their own from regular use. In some instances, they might also fail if your car has been improperly serviced.

On the other hand, some throttle position sensors are designed to last for the entirety of a car’s life, and may never fail. In general, however, the average lifespan of a throttle position sensor in a typical vehicle is about 80,000 miles. 

Can I Drive With a Bad Throttle Position Sensor?

Having a bad throttle position sensor is a pretty serious safety hazard, so if you have determined that the sensor in your own car is indeed not working, you should refrain from driving until you have it fixed, if possible. 

If you have no other options (for example, if you can’t get to your nearest auto repair shop without driving there), then you can probably get away with driving your car for a short while. However, you should go out of your way to avoid driving any longer than you have to if you have a bad throttle position sensor.

This is because, as we’ve mentioned, driving with a failed throttle position sensor can be quite hazardous. Such an issue could cause your car to stall or accelerate unintentionally at a particularly dangerous time. 

How to Replace the Throttle Position Sensor on a GMC Vehicle?

Replacing a throttle position sensor is a pretty simple process that you can do yourself at home as long as you have the necessary tools. If you’re not confident enough to perform this repair yourself, however, don’t feel bad about having to take your vehicle to the shop for this.

Assuming you do want to complete this repair yourself, however, here’s how to replace the throttle position sensor on a GMC vehicle:

  1. Before starting any repairs, make sure that the replacement throttle position sensor you have is a match for the old one. You wouldn’t want to go to the trouble of completing this repair yourself only to find out you got the wrong sensor.
  2. Using a socket wrench, disconnect the negative cable from your car’s battery to prevent any accidental electrocution from occuring.
  3. Remove the plastic cover over the engine, which will give you easy access to the sensor.
  4. Locate the throttle position sensor on the throttle body, and unplug the attached electrical connectors from it. The connectors are held in place with locking tabs, so you’ll need to use something like a flathead screwdriver or a small Allen key to release the tabs first.
  5. Once the electrical connectors have been removed, all that’s left to do is release the clips that hold the old sensor in place. You can do this by simply prying them off with a flathead screwdriver. There should be six clips holding the sensor in place.
  6. Once the clips have been released and the old sensor has been removed, you’ll need to remove the intake from the throttle body. There is a small pin in the throttle body that protrudes into the sensor, and removing the intake will allow you to manually adjust the throttle body and get the pin correctly lined up with the new sensor.
  7. When the new sensor is on, clip it back into place and reattach the electrical connectors. 
  8. Finally, replace your engine cover and reconnect your negative battery cable, and you should be good to go!

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