What Does Service Trailer Brake System Mean? (11 Causes & Fixes)

If you got a random warning light on your truck regarding your trailer brake system, you’re probably wondering: what does service trailer brake system mean?

A service trailer brake system warning message means that your truck is equipped with a wiring harness or integrated trailer brake control (ITBC) system that can control trailer brakes, and there is a problem somewhere in those components.

There can be multiple reasons for a “service trailer brake system” message or warning light, and we’ll go through how to diagnose and fix them in today’s guide.

Service Trailer Braking System: What It Means

ford f150 service trailer brake system warning

As we covered above, the fact you are getting a service trailer brake message means that your vehicle is equipped with some sort of equipment that can control trailer brakes.

That system is integrated in some vehicles that are commonly used for towing because heavier items like travel trailers or campers will have brakes on the trailer itself.

Connecting the trailer to the vehicle allows the vehicle to control those brakes on the trailer as well.

While this is convenient, the not-so-convenient part is when something goes wrong somewhere in that system and causes this error message.

That equipment can be as simple as a wiring harness or can be something else like an ITBC, or integrated trailer brake control system.

Either way, somewhere in this system something is causing the problem either in the wiring or the module itself.

You can get these messages popping up even if you haven’t towed anything with your vehicle, so it’s not your fault.

If you are planning on towing anything that is over 2,000 lbs, make sure the issue is fixed beforehand so your trailer brakes work.

We’re here to help you identify and fix it so you can get rid of that annoying warning message for good.

Common Causes & How To Fix Them

Chevy GMC Service Trailer Brake System

There are a few reasons that your integrated trailer brake control system or system wiring can be throwing this code, so we’ll need to look through each one.

Before you start, you should scan your vehicle for any diagnostic trouble codes (DTC codes).

You can do this by buying an OBD-II scanner, or most auto parts stores will scan your vehicle for you and give you a printout of the DTC codes for free.

This will help a lot with where on this list you should start troubleshooting.


Many truck owners report their service trailer brake light coming on after it rains or when there is high moisture content in the air and the truck is parked outside.

Usually after running the vehicle and restarting it later in the day, the code will go away.

This simply means that your system is sensitive to moisture and does not need any servicing.

ABS Light Is On With Service Trailer Brake System Code

If the ABS light is also on, fixing the ABS issue first will usually resolve the service trailer brake system problem on it’s own.

If it doesn’t turn off after clearing the ABS light, move on to the following steps in this guide.

Failed Trailer Brake Control

Replacing this switch on your dash takes less than five minutes and is a common cause of this annoying error message.

Check out this video to see how fast and easy it is:

Bad Fuse

Sometimes the fuse for your ITBC system can go bad, causing this code to pop up.

Fortunately, fuses are cheap and replacing them is easy!

Bad Relay

You may have problems with the trailer brake control relay and the connections that go to it from the wiring harness socket.

Most vehicles with a trailer brake control system will have the connections to the relay above the spare tire, so check those out and see if the relay is in good shape.

If you notice any corrosion or damage, you’ll need to replace the relay.

Dirty Wiring Harness Socket

Sometimes debris can get in the wiring socket and cause errors or bad connections.

Clean the connections up and put a little dielectric grease on them to keep them functioning properly.

Failed Master Brake Cylinder Pressure Sensor

Occasionally you will see the service trailer brake system light come on due to a bad pressure sensor on the master brake cylinder.

Depending on your skill level, you may want to bring the vehicle in to a mechanic shop so they can check this out and resolve it for you.

Trailer Wiring Problem

Sometimes if your trailer is wired incorrectly, it can cause the signals and feedback to your vehicle’s sensors that will throw this code.

Double check your trailer’s wiring to ensure everything is wired properly, and be sure you didn’t knock something loose during maintenance like adjusting your trailer brakes.

Bad Brake Light Switch

It sounds crazy, but this can be as simple as changing out a bad brake light switch or stop lamp switch to clear this annoying issue up.

Your Trailer Brake Controller Is Bad

If you have an integrated brake controller that you think has failed completely, usually replacing this with an aftermarket brake controller will be much cheaper than fixing the integrated one your vehicle came with.

Other Causes

Although it’s rare, you can sometimes see service trailer brake system warnings caused by issues with the ECM, TBCS (trailer brake control switch), TCBM (trailer brake control module), or ignition circuit.

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