Service Brake Trailer System – Causes and Solutions

If you are looking for a detailed guide about the service brake trailer system warning light on the dashboard of your car or your vehicle, you are at the right place. We will evaluate the general problems and the solutions of the service brake trailer system here.

You can find the possible causes and the general solutions to them. Also, you can find information about if it is an important concern or not. Let’s take a small look at the source of the problem.

What is Trailer Brake? Understand It Before Delving into the Service Brake Trailer System Problem!

Service Brake Trailer System Problem!
Trailer brake system. Image Source: Dreamstime.

This is the first question that comes to one’s mind. What is the service brake trailer system? Or what is the trailer brake? As you know that brake systems are very important for the safety of our cars and vehicles. Without them, we can not safely drive in traffic. And if the dashboard sign says something about the brake system of our vehicles, you probably get concerned about it.

First of all, we need to state that the trailer brake is not the main brake system of your vehicle. This is the brake system of the trailer that you attached to your tractor or your vehicle. It provides the braking of the trailer along with the braking of your car. So it is a very important thing for road safety.

Once you apply brakes in your vehicle, the trailer brakes are also activated. This activation takes place nearly at the same time that you apply the brake. And the slowing down effect made for the trailer also. Without the trailer brakes, you probably can not slow down effectively.

Also, there is a small control switch on your dashboard or your steering wheel to control the trailer brake. Like the main brakes of your vehicle, you can easily control the trailer brakes from that switch. This means it is also open to the control of the driver of the vehicle.

And we can talk about the real problem after this statement. We know it is very long but it was necessary.

How Does the Trailer Brake System Work?

Also if you want to understand the problem of the service trailer brake system message, you need to understand how the system works. First of all, it is an electrical thing that you can control with a switch. And also it is connected to the battery and the electrical system of your car. Also, this means, there is a fuse connection which is the electrical fuse.

Once you activate the switch, the trailer brake system activates. This means you complete the electrical circuit to activate the trailer brake system immediately. The electrical control system is connected to a mechanical system which is controlled by the electrical signals that come from the battery along with the fuse and switch.

After that, you can easily understand the possible causes of the service trailer brake system problems.

Why Service Trailer Brake System Sıgn Appears On Your Dashboard? What are the Causes?

Maybe you are asking this question yourself. And we know that you can imagine the possible causes of the problem after the statements and explanations that we made about this system. So, it will be very easy to understand the different possible causes.

Problems with Cable Connections

All the systems that we explained above are connected with the cables. These cables transmit the electrical signal between the different circuit elements. So, if there is a problem with the cable connections, the switch of your trailer brake will not work. And the warning light will come to your dashboard.

How to Test Trailer Brake System Cables?

You just need to test your switch. If it is not work, there can be problems with the cable connections. And it is quite hard to know which section ıof the cables is problematic. To test it, you need to use a multimeter.

You need to adjust the ohm measurement, you can put the ohm sticks to the different ends of the cable. Once you measure the ohm of the cable, you need to get a specific amount of ohm value which means there is a steady electrical resistance of the cable and there are no disconnections in the structure of the cable.

But if you read unrealistic Ohm numbers, this means this cable section that you are testing with the multimeter is problematic. Replacement of this section will solve your problem.

Also, it can be hard to find the battery and fuse sides of the cable connections. You will need to bring your vehicle to an expert if there is a problem with the cable systems.

Cable Replacement Costs

If you need to replace a cable connection to vehicle electricians, it will cost around $50-$70 according to the length and the place of the cable. This includes all the expenses.

Check the Electrical Connections

You need to check the battery connection of the trailer brake system if it is installed properly. In some instances, it can be disconnected from the battery. You need to check the – pole section and you can find different electrical installations. Check the user’s manual of the OEM trailer brake system to locate the connection.

Check the fuse connection and the brake connection system.

Broken Service Trailer Brake System Control Switch

Also, there can be a problem with your control switch. If the switch is faulty, the trailer brake system simply will not work properly. This means you need to replace it with a new one.

If you are curious about how to understand if the switch is a problematic part, you just need to detach the switch system and barely take the cables. And touch these bare cables to each other to see if the brake system is activated. If the system works properly with this method, your trailer brake switch application is a problematic part.

How Much is the Replacement Cost of a Trailer Brake Switch?

You probably trhşnkingabout this question but replacement of the trailer brake switch is not a very high price thing. You just need to buy a cheap switch and bring your vehicle to an electrical expert. Or you can make the contacts and replacement by yourself and probably all the expenses will not exceed around $20-$30.

Blown Fuse

If there is an excessive electrical current on the electrical control system, the fuse will be blown to protect the other electrical connections from very high voltage. So, it is not a bad thing to happen. What you need to do is to replace the blown fuse with a new one.

The fuses are not high priced things. But you need to know the number of the location of the fuse inside the fuse box of your vehicle. The fuse box is generally located below your steering wheel section or in the hood. Take a look at the number of the fuse of the trailer brake system and replace it with a new one.

How Much is the Fuse Replacement of Trailer Brake?

The fuses generally cost around $4-$5. If you think that you can not make it by yourself, you just need to bring your car to a car electrician. They will make it around $10 for you. This is the most simple problem that you can face with the trailer brake system of your vehicle.

Problematic Brake Light Switch

Another reason for this service trailer brake system is the problematic brake light switch. Maybe there is a problem with the brake light switches which is very important to inform other people on the road if your trailer brakes are activated by you or by the vehicle. So, if there is a problem with the brake light switch you need to replace it with a new application.

Also, the replacement of this switch is not very high price and it is generally the same as the trailer brake switch. You just need to test it and if it is a problematic part, you need to replace it with a new application.

Problematic Master Cylinder and Sensors

Problematic Master Cylinder and Sensors
Master cylinder of a typical vehicle. Image Source: Repairsmith.

The master cylinder is the system that provides the required amount of hydraulic fluid at high pressure to all the brake systems. And trailer brake system takes the brake fluid from this system. The master cylinder is generally placed under the hood of your truck or your vehicle.

And also there are a bunch of sensors that run the trailer brake systems in general. And if there is a problem with these sensors and the master cylinder, you need to understand that you have a much bigger problem. Because these problems can affect the main brake system also. You need to bring your vehicle to service as soon as possible to take care of the general problems.

If we talk about the general replacement prices, it can be very high if we compare them with the other parts in general. You can pay up to $200-$300 according to the size of the problem that you are facing in general.

How to Diagnose the Service Trailer Brake System Problem?

In general, these kinds of electrical and mechanical problems are generally diagnosed with OBD scanner systems. They attach this scanner to the vehicle and see if there is a problem with the general things.

  • The first step is to diagnose with the OBD scanner. If there is a problem with the sensors and the general electromechanical systems of the trailer brake application, the OBD sensor will indicate the problem.
  • If there is no problem or if there is no indication on the OBD scanner, you need to check the fuse box. You can do it by checking the fuse box of your vehicle. If you see there is a blown fuse in the fuse box, you can replace it with a new one.
  • If there is no problem with the fuse of the trailer brake system. Check the switches. You need to check the brake switch and brake light switch respectively. Just detach them and make contact with the two cables on these switches. If the brake system and the brake light work, we can say that there is a problem with the switch itself.
  • And also if there is no problem with the switches, you can check the cable connections and faulty cables in the system. You can make it as we explained above. You can use a multimeter.
  • And if you find out that there is no problem with any of these systems, this means you have a much bigger issue with your brake system. You need to bring your car to service immediately.

How to Reset the Service Trailer Brake System Warning Signal?

Once you solved the problem, you want to turn this service trailer brake system warning signal from your dashboard. There are various steps that you can follow if you want to remove this signal from your dashboard.

  • First of all, you need to find the adjustment nut on the trailer brake system. Take a look at the brake systems of the trailer. These nuts are generally situated in the back of the trailer brakes. If you can not find it, you can check the axle side aşso.
  • You need to have a screwdriver to loosen this lock nut completely. This will allow you to reach the adjustment nut.
  • With this adjustment nut, you need to rotate it to a clockwise section. You need to be sure that it snugs to the backing plate. And you should not tighten too much.

After these steps, the signal will disappear from your dashboard without any problem.

Is It Safe to Drive with Service Trailer Brake System?

This is also a question that lots of people are asking about the brake system of trucks and vehicles. No, it is not safe to derive with the service trailer brake system. Because you do not know the real source of the problem that you see in your system. So, it is very important to assess the situation visually.

As you see above there can be different sources of this problem. And you need to make your assessment wisely to see that you can solve the problem. And if the problem arises from the main brake system, driving with this warning light on the screen is not a good idea to consider.

You just need to bring your vehicle to a service point to see if there is a major or minor problem with the service trailer brake system.

Different Types of Trailer Brakes

 Also if there is a problem with the general brake system of your vehicle, you need to know which type of trailer brake your vehicle has. There are different kinds of them.

  • Electrical systems: Electrical trailer brake systems are the most common applications in modern trucks and vehicles. Because the control of the trailer brakes with the electrical applications is much easier than the other systems. This means you can easily control the different kinds of applications without any problem. But electrical systems are more complex systems than hydraulic or mechanical systems. There are sensors, controllers, etc that make the repair and diagnostic of the brake system harder.
  • Hydraulic systems: The working principle of the hydraulic trailer brake systems is very simple. Once you press on the brake pedal, the vehicle will decelerate. And there will be momentum occur because of the inertia of the trailer. There is a hydraulşşc pişston that contains hydraulic fluid inside it will be pressed with the inertia of the trailer. And this hydraulic fluid will rush into the brake pads of the trailer system which will create additional braking. These mechanical applications are generally much more simple systems if we compare them with the other applications. And maintenance will be much easier if we compare it with the electrical system.

Service Trailer Brake System Problems in Different Models

As you know that there are different models available in the market. And if your truck is one of them, you can easily diagnose and solve your problem.

  • RAM 1500: This is one of the most common trucks and pickups in the US. And if you have one of them, you are the lucky one. Because most of the problems are generally caused by not snugged adjustment nuts. You just need to adjust the nut as we explained above. It will make the situation much easier.
  • GMC Sierra: In general if you get the service trailer brake system warning with your GMC, the real cause of this problem is generally the ITBC system. ITBC is the controller of your trailer brake. And if you want to solve the problem, you just need to replace it with a new application.

Conclusion on Service Trailer Brake System

So as you see above the solution of the service trailer brake system is generally very basic. But, if you have a major problem with our brake system, you need to bring your vehicle to service.

If you have additional comments and questions about this topic, please leave them below. Your precious feedbacks are very important to us.


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Uğur Uygun

Hello everyone, I am Uğur. I am a mechanical engineer who has experience in different R&D departments of HVAC companies. With my best friend, I decided to build this website to share out knowledge and experience. And also, I am interested in automotive. So, I am writing about automotive and automotive-related articles here. Sharing my knowledge and experiences on these topics is a very big pleasure for me. I am willing to answer all of the questions people have about these topics.

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