How To Fix Service Trailer Brake System?

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Service Trailer Brake System

The trailer brake system is one of the most underrated features in Chevy and GMC vehicles.

That’s because not many owners use it (as they don’t have a trailer to attach). But those who use it can’t seem to live without it.

For the latter, the ‘service trailer brake system’ message is not a good sign, especially if it appears while they’re towing a trailer.

However, before you rush out to the dealership, it’s important to do an initial diagnosis.

That’s because this message can also appear due to minor issues you can easily fix at home.

How To Turn Off the ‘Service Trailer Brake System’ Message?

The best way to reset the service trailer brake system is to fix the malfunctioning component that triggered the ECU to generate this message.

These components include the trailer brake control switch, brake fuse, controller relay, trailer connector, and wiring connections.

You can also try disconnecting the negative battery terminal, but its chances of resetting the message are low because it’ll only work if there is some electrical issue that triggered the message earlier.

What is the Trailer Brake System?

The trailer brake system is a safety feature in Chevy and GMC vehicles designed to aid the driver when the trailer is attached.

In normal circumstances, the additional weight of the trailer can negatively affect the vehicle’s braking system.

It can increase the stopping distance (increasing the risk of accidents) and put extra pressure on your vehicle’s brakes, causing them to wear down quickly.

The trailer braking system solves this problem by having an additional brake controller for the trailer.

This controller is in sync with the vehicle’s braking system, meaning whenever you apply the brakes of your truck, the brakes are automatically applied to the trailer simultaneously.

More importantly, this system allows the driver to set the braking force according to the trailer’s weight and load conditions.

Modern trailer brake systems also feature an electronic control interface that enables the driver to monitor and control the trailer brakes directly from the vehicle’s dashboard.

What Does the ‘Service Trailer Brake System’ Message Mean?

The ‘service trailer brake system’ warning message indicates an issue with the integrated trailer brake system.

Based on my observations, it occurs mainly on Chevy Silverado (2014, 2015, and 2018 models in particular) and GMC Sierra vehicles.

In most cases, it appears when an internal component of this system, such as the trailer connector, trailer brake control switch, trailer brake continue relay, etc., is malfunctioning.

Therefore, to turn off this message, you’ll need to fix the faulty component that triggered this message in the first place.

The main reason why this error is confusing the truck owners is because sometimes it appears even when no trailer is attached.

How to Fix the Service Trailer Brake System In Chevy Silverado?

As the service trailer brake system consists of many smaller components, you’ll need an OBD-II scanner to determine which one is malfunctioning.

We can also solve this issue without a scanner, but it’ll make the whole job much longer as we’ll now have to check each component individually.

1. Check the Trailer Brake Control Switch

Check the Trailer Brake Control Switch

The first component we’ll check is the trailer brake control switch, especially if the scanner is giving the C1117 code.

Located on the left side of the steering column, this switch/slider is part of the trailer brake system’s control panel and is pushed towards the left side when the driver wants to apply the trailer brakes manually.

Besides this switch, the control panel has two additional buttons to adjust the maximum braking output.

This switch can wear out or accumulate dust/corrosion over time, leading the ECU to generate the service trailer brake system message.

If this switch is dusty, you’ll need to clean the inner circuit with isopropyl alcohol. But if it’s physically damaged, you’ll have to replace the switch assembly.

Here’s a rough overview of this process:

  • To access the switch, we’ll have to remove the fuse cover panel first – using the trim removal tool.
  • Pull out the vent panel.
  • Unplug the wire harness that’s connected to the switch. However, if its connector is already loose, it’s possible that the switch itself is working, and the error message is appearing due to a loose connection. In such a situation, you should replug the connector and see if anything changes.
  • Remove the switch assembly.
  • Put the new switch assembly in its place.
  • Connect the wiring harness.
  • Fit the vent panel back into its place.
  • Put the fuse cover panel back on.

You can also watch the video below for further help.

Although it’s rare, sometimes you might get the error message even after replacing the control switch.

It indicates that the problem is in the switch’s harness (it’s either open or shorted), and you should test it with a multimeter.

2. Check the Trailer Brake Fuse

Check the Trailer Brake Fuse

The Chevy Silverado and GMC Sierra vehicles have a dedicated trailer brake system fuse.

This fuse provides electrical power to the trailer braking system and blows if there’s an electrical overload or a short circuit within that system.

If it blows, the circuit will become open, and the trailer brake system will not get any power, resulting in the ECU triggering the warning message.

To confirm whether that’s indeed the case, you’ll have to check this fuse with a multimeter and replace it if it’s blown.

You’ll also have to check the owner’s manual for the location and labeling of this fuse, as both of these things vary between vehicles.

3. Check the Trailer Brake Controller Relay

Check the Trailer Brake Controller Relay

The trailer brake controller relay can be another reason for the service trailer brake system message.

Usually located in the spare tire area of your truck, this relay allows the current to flow to the trailer brake controller.

This relay and/or its connector can get dirty over time, resulting in a poor connection and that error message by the ECU.

In such cases, the best option is to clean the connector and use a new relay (it costs 35-40 bucks) to see if the error goes away.

Watch the video below for more info.

4. Check the ABS Sensor(s)

Check the ABS Sensors

If you’re getting the service trailer brake system message in addition to the ABS warning light, one of the ABS sensors is most likely to be the culprit.

Each ABS sensor calculates the rotational speed of its corresponding wheel and sends that data to the ECU. The ECU uses the data from these sensors to prevent the wheels from locking up during slippery conditions.

In many vehicles, the ABS is linked with the trailer brake system. So when one of the ABS sensors malfunctions and causes the ABS not to work, it also indirectly affects the trailer brake system.

In such a situation, you’ll need to test each ABS sensor with a multimeter. This process roughly goes like this:

  1. Set the multimeter to the resistance mode.
  2. Connect the multimeter probes to the terminals within the ABS sensor’s connector.
  3. Check the resistance reading on the multimeter’s display. It should be in 800-2000 Ohms and consistent across all ABS sensors.
  4. If the reading is outside that range and/or is different than what you got for ABS sensors on other wheels, this ABS sensor is not working and should be replaced.

Check out this video for more information in this regard.

5. Check the 7-pin Trailer Connector

Check the 7-Pin Trailer Connector

The trailer connector, also called the trailer plug, is the component that connects the electrical systems of a tow vehicle and a trailer to synchronize the essential functions such as brake lights, turn signals, and tail lights.

Chevy Silverado vehicles come with a 7-pin trailer connector that is also used to transfer power for electric brakes and auxiliary power for the trailer’s interior functions.

If the wiring harness to the trailer connector has a damaged/frayed wire, its corresponding function will not work in the trailer.

The ECU will detect this as an issue and display the service trailer brake system message. In addition to this, it may also generate the C1596 DTC code.

The good thing is that this problem is pretty easy to diagnose. All you need is a trailer light tester, such as this one.

Plug this tester into the connector, turn on the vehicle, and perform different functions, such as turning on signal/tail lights, applying trailer brakes, etc.

If you perform any of these functions and the corresponding light on the tester does not turn on, it means that the wire providing signal/power for that function is not working.

Sometimes, it can also happen due to dirty/loose connections, especially if you get the error message when no trailer is attached.

Therefore, check for all possibilities before reaching any conclusion.

Conclusion

These were some common reasons for the service trailer brake system warning message on your Chevy/GMC truck.

If you’ve checked all the components mentioned above and the message is still there, I recommend going to the dealership.

That’s because, at this point, it looks like the culprit is the trailer brake control module or the trailer brake controller.

Since testing/replacing these components is too technical for most truck owners, you should leave it to the professionals.

Frequently Asked Questions

Why Does My Truck Keep Saying Service Trailer Brake System?

Your truck keeps saying service trailer brake system because the ECU has detected a fault in the trailer brake system, which can be dangerous if you’re towing at that time. This message is there to alert the driver.

What Causes Trailer Brake System Failure?

Hardware malfunction, incorrect trailer brake adjustments, poor connections, damaged/shorted wiring, and blown fuse are some common causes of trailer brake system failure.

Can you Turn Off the Trailer Brakes?

Yes, you can turn off the trailer brakes by unplugging the brake controller.

Is it Safe to Drive with the Service Trailer Brake System Message?

Yes, if you’re getting the service trailer brake system message when no trailer is attached, you can drive it safely.

But if it happens while you’re towing, take the vehicle to the dealership as soon as you can because it can potentially cause an accident.

Do Trailer Brakes Run Off the Trailer Battery?

No, the trailer brakes are powered by the trailer brake controller. This controller, in turn, gets powered by the towing vehicle’s battery.

However, trailers also come with a built-in auxiliary battery as part of the break-away system.

This system is designed to automatically engage the trailer’s brakes in case the trailer becomes disconnected from the towing vehicle while in motion.

Why Does My Chevy Silverado Say ‘Check Trailer Wiring’?

The ‘check trailer wiring’ error message on Chevy Silverado mostly appears due to a faulty trailer plug, damaged wire(s), or a bad ground connection.

AUTHOR
Andy is an avid car enthusiast with over 5 years of experience in DIYing auto maintenance. He founded AutoProblemz to share his knowledge and expertise with others through writing. His aim is to cut through jargon and help you make the right decisions for your vehicles.

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