John Deere 750C: Common Fault Codes and Ways to Fix the Machine

Despite being an older model, the John Deere 750C crawler dozer can still put in a lot of work. With some elbow grease and lots of love, this machine will not betray you. However, that means you need to understand its many fault codes to properly take care of it.

Thankfully, trying to understand each fault code that flashes on the panel screen is not a difficult task. More often than not, resolving each fault code is a lot easier than most people usually imagine. Just knowing how to properly care for and clean your machine is enough to fix most issues.

To start with, there are so many fault codes wired into the machine that it's impossible to get through all of them in one sitting. That's why it's best that you learn what the common fault codes are that almost every owner will face in their lifetime. The most common fault codes are the following:

• F627 Fault Code
• F628 Fault Code
• F635 Fault Code
• F640 Fault Code
• F647 Fault Code
• F668 Fault Code
• F675 Fault Code
• F691 Fault Code

On top of learning what each fault code means and how to fix each one, you will also learn what the most common problems are that every crawl dozer faces. Learning all of this will help save you a lot of time in trying to figure out what the problem is and what are the appropriate measures to take. So continue reading until the end of the article to find out more.

John Deere 750C Fault Codes And Ways To Fix Each One?

As mentioned earlier, fault codes are not there to complicate things. Instead, they exist to make your life easier. And when it comes to the John Deere 750C, they are very handy in identifying what problem you're facing so you know what are the proper ways to take care of each problem.

Normally, a crawler dozer has several fault codes programmed into it. And the same is true with the John Deere 750C crawler dozer. Learning all of them will take up a lot of your time, and not all of them regularly come up.

But today, however, you will learn what the common fault codes are that a John Deere 750C crawler dozer commonly faces and how to fix each one. Make sure to read each one carefully to understand their differences and similarities.

1) F627 Fault Code

What this usually means is that the speed sensor went bad or there's a wiring issue. Commonly referred to as a "steering sensor fault," you will have difficulty increasing the speed of the machine or putting on the brakes. Luckily, resolving this issue is quite simple.

First, you need to locate and remove the rear track cover. Doing so will give you access to the transmission control unit, or TCU, for short. Then, check the wires and speed sensors of the machine for any obvious external damages.

The easiest thing to do here is to swap out the speed sensors with a functioning one to check if the problem persists. If not, then your machine was suffering from bad speed sensors. If the problem continues, you will need to check the wires.

Make sure that there are no loose connections and tighten up the thread carefully. Then, do a quick calibration of the wires with functioning speed sensors.

2) F628 Fault Code

Similar to the previous one, this fault code also involves speed sensors and wiring. In this case, what happens is that your machine will suddenly veer to the right while driving before coming to a sudden stop. What this means is that the speed sensor responsible for tracking the movements of the machine's left side is not functioning properly.

Just like what you did in the previous fault code, you need to check for any damages to the speed sensors, wires, and harnesses. Swap out the speed sensor with a functioning one and make sure to recalibrate the wires. This is enough to resolve the issue.

If you continue to have issues with the speed sensors and the steering, then take your machine to a specialized shop and have a professional take a look. Something else may be at play, especially if the machine has put in a lot of work over the years.

3) F635 Fault Code

When swapping out the speed sensors, it's common for another fault code to flash on the screen panel, especially if it's your first time doing this sort of repair. This fault code could mean two things; one, you used the wrong speed sensor on either side, and two, you did not adjust the connection properly.

Resolving the first one is easy enough. It's the second one where you can have a little bit of trouble. It's better to hire a professional who has experience in resolving this issue to avoid damaging the speed sensors and the speed ring.

4) F640 Fault Code

The John Deere 750C crawler dozer makes use of an early iteration of the hydrostatic pump. While it shows great performance, you also run into this fault code quite often.

If the machine is throwing out this code, it means that you either have a broken hydrostatic pump speed sensor or the sensors need careful adjustment. Try swapping out the speed sensor first and see if it helps clear out the code. Afterward, try tightening the nuts on the speed sensors until you achieve the sweet spot.

Normally, it will take a while to clear this code, especially if it's your first time. If you don't want to go through a trial-and-error process, bring your machine to a professional.

5) F647 Fault Code

If you're having trouble making your crawler loader startup and run, then this is most likely the code that will come up upon checking. Not only is this one of the more common fault codes that your machine will encounter, but it also requires you to perform a maintenance check on quite a few parts.

First, you need to check the hydraulic fluid. Make sure that the machine has the required amount and that it's not old fluid. Additionally, clean out the transmission filters or replace them if necessary.

Having too little or too much transmission fluid can cause the machine's sensors to go out of whack. That's why it's important to always follow the recommended amount for your machine. Also, cleaning out and replacing the filters is necessary to ensure that the fluid will flow properly.

Next, check the fuel pressure regulator for any damage. Oftentimes, replacing this with a working part is more than enough to solve the issue.

6) F668 Fault Code

If this code flashes on your machine's panel, then you're likely dealing with an electrical wiring issue. This fault code is quite common due to how old the John Deere 750C crawler loader model is.

Usually, improper storage or neglect in maintenance are the most common reasons why the machine is suffering from this fault code. Upon opening the transmission panel, it's common to see the insulation of the wires peeling off and some corrosion taking place.

A machine suffering from this fault code can't move around. That's because both the left and right steering sensors are not functioning due to the wiring issue.

Simply cleaning it out and replacing the wires will help you clear out the code. However, if you have no experience dealing with electrical wires, it's better to hire a professional.

Also, if the machine has spent a long time in storage, it's better to take it to a professional shop. It's quite common for there to be other issues that need professional assistance.

7) F675 Fault Code

This is another common fault code that a lot of owners face when using this machine. The panel will start flashing this code if the crawler loader refuses to drive in reverse and always moves forward.

You're likely dealing with an intermittent issue with the transmission controller connectors. What you need to do is disconnect all the connectors and check the resistance. Use the manual to help guide you.

Sometimes, the initial issue won't show up even after checking the connectors. So instead, it's always best to clean out or replace the transmission controller connectors. Doing any of these will help get your machine moving backward in no time.

To Wrap Up

The John Deere 750C crawler loader holds a special place in many people's hearts. Not only is it one of the crawler loaders to make use of an early hydrostatic pump design, but it's also one that many bought in their earlier days and still make use of to this very day.

Because of that, however, it's quite common for the machine to go through some rough patches. And that's where learning the common fault codes that this machine usually faces comes in. Not only will it allow you to understand what sort of problem your machine is facing, but you will immediately know what are the proper steps to take, ensuring that the machine will continue to pour in more work for the next few years.