5.9 Cummins Accelerates On Its Own – Why And What To Do?

Smooth driving requires a good engine for you to arrive safely to the location. But sometimes, cars act up badly, and it must be risky when your truck suddenly accelerates by itself. We heard you needed it, so here's what we found out!

A failing throttle can cause the 5.9 Cummins, as well as other engines, to accelerate by itself. The APPS signals the ECM, so the throttle reacts, making the speed change if a problem arises. When that happens, you should check and adjust the acceleration position of your pedal.

Discovering the reason behind the accelerating engine on its own may not be enough. So, in this article, we'll understand deeper the symptoms and how to prevent them from worsening. Keep on reading so you will know later how to check up on your engine before driving away.

The turbocharger is visible on a Cummins diesel engine - 5.9 Cummins Accelerates On Its Own - Why And What To Do

The Creation of 5.9 Cummins

New turbo for a 5.9 cummins diesel

The mostly known 12v or 12-valve was the drive-by-wire 5.9 Cummins engine produced in 1984 by the B-series diesel engine. In 1998, the 12-valve or 6BT was soon changed to Interactive System B or ISB. 

Since the version has changed to ISB 5.9, the valves and cylinder have changed as well. It then produced the six cylinders with four valves each, called 24v or 24-valve. 

The engine was primarily used for trucks, and it was ramping despite its six cylinders against the eight cylinders of the competitors. It maybe lacks power, but its diesel engine was quite famous.

It was known as fuel efficient, simple design, and the parts that are budget tolerable. In fact, you can buy some parts through OEM or aftermarket.

In 2007, the 6.7L Cummins was created, but it was also the last version of the 5.9 Cummins. It was refrained from production because of the tightening emission regulations.

How Does the APPS Works?

Before jumping into the solution, you must first understand the root cause of the 5.9 Cummins engine, which is the APPS. With that, we will elaborate first on the APPS function and how it occasionally fails.

The APPS is usually located above the gas pedal, whereas it follows the pedal's movement and spreads the gas to the engine. It sends a signal to the ECM or PCM that makes the throttle response, either to open or to close, to the air and fuel of the car.

This process affects the RPM or speed of the engine.

If the said premise has been carefully followed, then you are assured of a good ride. But if the ECM fails to receive a signal from the pedal, the throttle will remain open. The worst scenario can be speeding up high or slowing down abruptly by itself. 

This is typically happening with the 1998-2004 version of the 5.9 Cummins engine, and if the APPS is malfunctioning, do not take the risk anymore because your truck and your life are at stake.

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Knowing the Symptoms of Bad Accelerating Pedal

Defective Engine's Light

To check the engine's light, use the OBD2, and you will get to scan which sensor is malfunctioning. For example, if you receive codes like P2122, P2123, P2127, or P2128, then it is said to be an indication of problems in your APPS. 

Checking the light has no huge remedy to the car but knowing that it has a problem, then you will already have an idea that the sensor has problems too. 

The Engine has Rough Idle

If the engine has an issue with the idle, it will be impossible for the PCM or ECM to record the appropriate voltage. If the recorded voltage is higher than it should be, then it is likely to cause accidents on the roadway.

Failed Reaction in Pedal

After pressing your foot on the gas pedal and the response is taking too long, then you will likely lose the speed than the normal basis. 

Failing to receive the signal from the APPS means late operation. It is because the transmission is rooting for the throttle's input to decide what movement it should do. 

In some cases, the gas pedal is completely dead when pressed, and with that, the car cannot also respond. Better bring it immediately to the auto service center to identify why the gas pedal does not work at all. 

If your car is already experiencing this symptom, no doubt the problem is the position of the acceleration pedal.

Checking Acceleration Position Pedal

Close up Leather Shoe ob pedal in car

Since we already made a breakdown of the malfunctions of the APPS, the next move is to diagnose the position of the pedal. Again, doing it is highly manageable, especially when you have the right tools.

Note that you can bring the car instead to the auto service if you are reluctant to do so. Moving forward, here are the basic steps from testing to replacing the sensor below:

  1. Use the OBD2 tool to locate which sensor is malfunctioning. If the codes displayed aren't the optimum ones, then the sensor has a problem.
  2. Second, use the multimeter to detection of the voltage.
  3. Locate the sensor, which is mainly found above the gas pedal or at the firewall engine bay. 
  4. Use a socket and wrench to remove the bolts of the sensor's cover.
  5. Check the wirings that connect to the sensors and unplug them.
  6. Move the bracket that is between the AC lines and the strut power. Then twist the sensor to release the tension to the cable.
  7. Now use the wrench to release the cable from the bracket. This process is loosening the nut that holds those two devices. By this time, you should be already holding the bracket.
  8. Use the socket to remove the two bolts that hold the bracket and the old sensor together.
  9. Hook the tail end of the new sensor to the cable and secure it by springing back. The nuts that hold the cable and the bracket should be tightened enough, then return the bracket and the cover you removed earlier. That's quite everything, and you're done!

Survival Tips on an Accelerating Itself

The turbocharger is visible on a Cummins diesel engine.

If the car suddenly changes its speed while you are driving, a lot of things might happen around. But with mindfulness, you can avoid the worst possibilities. To guide you when things like this suddenly happen, here are the things you should take note of.

Do Not Panic

Having no control over your speed while the car is on the road is indeed nerve-wracking. But you have to breathe and try to calm down and try your best to think about the next move.

Opt to Neutral 

Choose the Neutral option to return your car on the straight way. If this option is not applicable, turn off the engine immediately. When you turn off the engine, make sure that the key is intact in the ignition to prevent a stuck steering wheel.

Hit the Break

There is vacuum assistance, so what you can try at that moment is to hit the brake pedal. If that did not work, choose the emergency break to slow down the car's speed.

Find A Safe Area

When the car is already slowing down, find a spot or area to park. Make sure that there will be no pack of people or fragile things around. Once done, turn off the engine and safely exit. When you are already out of the car, call a towing service to help you out with it.

Frequently Asked Questions

What happens if you overrev a diesel?

Overreving can damage the valve. Due to this instance, the valve remains either open or close for a longer time. If this happens, the valve will float, and that will result in an unwanted power loss of your engine.

What is high mileage on a 5.9 Cummins?

Surprisingly, the 1996 Dodge Ram of 5.9-liter Cummins has 3,016,789 mileage. This record proves the edge of this version to think that most of the car engines can barely reach 150,000. Even if they do, their engine is mostly damaged.

Is a 5.9 or 6.7 Cummins better?

The 5.9 Cummins version might be famous, but in terms of upgraded one, the 6.7 provides better performance. In addition, the 6.7 Cummins has better emission control features that aren't included in the 5.9.

Its highlight was the big exhaust brake which is commonly used for towing machines.

An engine of Cummins Inc. is displayed during an exhibition in Beijing, China, 17 May 2012 — Stock Editorial Photography

Final Thoughts

If the car is self-accelerating, then it's dangerous to continue the ride anymore because a lot of underlying risks are there. But knowing the reason behind like the symptoms can prevent the worst-case scenario.

The steps on how you can fix the accelerator are pretty much handy so that you can do it anytime soon. Also, your budget can save some costs with the right tools and attention to detail. However, it's also possible to buy a new one instead since Cummins' parts are known as affordable.

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