Trailer ABS Light Comes On When Brakes Applied

Trailer ABS Light Comes On When Brakes Applied 

Ensuring the safety of your cargo and fellow road users is of utmost importance. One crucial safety feature of trailers is the ABS, designed to prevent the wheels from locking up during hard braking. However, if the trailer ABS light comes on when the brakes are applied, it’s vital not to ignore it. 

There might be several underlying issues that turn on the ABS of your trailer when braking. The trailer ABS light coming on when brakes are applied can be a result of the following:

  • Wheel speed sensor issues
  • Damaged ABS rings
  • Low brake fluid level 
  • A faulty ABS pump

In this article, we will explain the potential reasons behind this issue in detail. Also, we’ll guide troubleshooting and resolving the problem to ensure safer travels.

Why Does ABS Light Come On During Braking?

The ABS system significantly enhances braking safety for trailers by reducing the risk of skidding and jackknifing. It enables drivers to maintain steering control, thus avoiding potential accidents or collisions. This feature is especially crucial when hauling heavy loads or navigating challenging terrains. 

Why Does ABS Light Come On During Braking

If the ABS system is deliberately or accidentally deactivated, you’ll notice that the ABS light will come on while applying brakes. However, there are other  reasons for the ABS light to illuminate, which include

Wheel Speed Sensor Issues

These sensors monitor the rotational speed of each wheel and send data to the ABS control module. When a sensor fails, is corroded, or sends incorrect signals, the ABS system will interpret this as a problem and trigger the ABS light. 

A Faulty sensor or wiring issue causes wheel speed sensor issues.

Trailer Wheel Speed Sensor Issues


Examine the wheel speed sensors for visible damage, debris, or corrosion. Take the necessary actions accordingly. Here are the steps you should go through. 

  • Before proceeding with the wheel speed sensor cleaning, turning off the trailer’s power is essential to prevent any electrical hazards.
  • Identify the wheel speed sensor near the brake rotor or hub assembly.
  • Detach the sensor from its mounting bracket, which could be secured by either a bolt or a clip.
  • Use a clean rag to gently wipe the sensor until it is free of dirt and debris. Or you can use a soft-bristled brush to remove it with care. Refrain from using any chemicals to prevent potential damage. 
  • Confirm that the sensor is securely connected, properly fastened, and free from any damage.
  • If any of the sensors is damaged, replace it/them. 
  • Place the sensor back into its mounting bracket and fasten it securely using either the bolt or clip.
  • Turn the power back on and proceed to test the ABS system to verify its proper functionality.

Faulty ABS Pump or Module

The ABS pump and control module are integral parts of the system. If either of these components fails or is damaged, the ABS light will trigger. This indicates a problem with the system’s functionality. Locking wheels and brake pedal malfunctions are signs of a faulty module.

Trailer Faulty ABS Pump or Module


  • Replace with a new ABS module. However, this can be an expensive repair. Hence, you can rebuild or repair your current module with the help of a professional. It’s a complex repair and you may not be able to handle it.
  • Replace or repair damaged components with a new or refurbished unit and ensure proper calibration. 

Damaged ABS Rings or Wiring

ABS rings are toothed rings mounted on the wheel hub. They work in conjunction with the wheel speed sensors. Damage to the ABS rings or issues with the wiring connecting the sensors will disrupt the proper functioning of the ABS system. 

Read:  Why Is My ABS And Traction Control Light On At The Same Time?

Thus, once you apply the brakes, the ABS light will illuminate, indicating a malfunction. 

Trailer Damaged ABS Rings or Wiring


  • Check the ABS rings for damage or debris. If the rings are damaged, you’ll need to replace them with new ones. Meet an auto mechanic for a replacement. 
  • Additionally, inspect the wiring harness connected to the wheel speed sensors for any visible issues. Consult a professional auto mechanic to fix the wiring harness.

Low Brake Fluid Level

Some trailers have a brake fluid level sensor integrated with the ABS system. If the fluid is insufficient, it activates the warning light. The reservoir has lines marked as “Min” and “Max”. The normal brake fluid level will fall in the middle. An insufficient fluid will fall below the “Min” line. 

Trailer Low Brake Fluid Level


Inspect the trailer’s brake fluid reservoir and top it up with the manufacturer’s recommended brake fluid if needed. Here are the steps to check the fluid level in the trailer ABS system:

  • Park the trailer on a level surface and engage the parking brake for safety.
  • Locate the brake fluid reservoir on the trailer. It is usually near the master cylinder.
  • Remove the reservoir cap by twisting it counterclockwise.
  • Use a flashlight if needed to inspect the fluid level. The fluid should be between the minimum and maximum marks on the reservoir.
  • If the fluid is low, add the manufacturer-recommended (DOT 3 or DOT 4) brake fluid until it reaches the appropriate level, that is between the “Min” and “Max” lines in your reservoir.
  • Avoid overfilling the reservoir, as it can cause issues with the brake system.
  • Securely replace the reservoir cap and ensure it is tightened properly.
  • Start the trailer’s engine and test the brakes to ensure they are functioning correctly.

Fuse or Relay Problem

A fuse and relay protect the electrical components of your car from getting damaged in case of a power surge. But when the fuse gets blown or the relay is faulty, the electrical system will begin to malfunction. Therefore, once the ABS system detects a problem with its components or power supply, it triggers the ABS light on the dashboard to illuminate.

Trailer Fuse or Relay Problem


Check for any blown fuses or faulty relays and replace them accordingly. Here are the steps to replace the blown fuse

  • Turn off the trailer’s engine and remove the key from the ignition. Engage the parking brake for added safety.
  • Locate the Fuse Box in the engine compartment, near the battery, or inside the cabin. 
  • Identify the blown fuse, which will have a discolored or visibly broken or melted wire inside it.
  • Remove the Blown Fuse with a fuse puller or a small pair of pliers. Next, select the correct replacement Fuse with the amperage rating printed on the blown fuse.
  • Take the new fuse and carefully insert it into the empty fuse socket. Ensure it is pushed in firmly but not forced.
  • Test the ABS System. With the new fuse in place, turn on the trailer’s ignition (without starting the engine) and check if the ABS light comes on and then goes off. This indicates that the ABS system is functioning correctly.
  • Once you have confirmed that the ABS system is working, securely close the fuse box cover.
Read:  Honda Civic ABS Light On: Common Causes and How to Reset

If the above steps do not resolve the issue or if you are uncertain about troubleshooting, it’s best to take the trailer to a qualified mechanic. You should also visit the trailer service center for a thorough inspection.

How To Reset The Trailer ABS System After Fixing The Issue?

How To Reset The Trailer ABS System After Fixing The Issue

Here are the steps to reset the trailer ABS system after fixing the issue

  • Ensure that the ABS problem has been properly diagnosed and repaired by a qualified mechanic or technician.
  • To ensure the ABS system is completely powered off, disconnect the trailer from its power source, whether it be the tow vehicle or electrical outlet.
  • Provide a few minutes for the ABS system to reset fully and discharge any remaining power.
  • Reestablish a secure and proper connection between the trailer and the power source.
  • Depending on the power source, either activate the trailer’s electrical system or turn on the ignition switch of the tow vehicle.
  • Keep an eye on the ABS light on the trailer. It should briefly illuminate when the ABS system powers on and then go off after a few seconds, indicating proper functionality.
If you’ve noticed that the ABS light on your trailer comes on when the brakes are applied, our article on Jeep Wrangler ABS light concerns might provide insights that could assist in addressing similar situations. Furthermore, if you’re a Honda Civic owner dealing with an ABS light issue, our guide on Honda Civic ABS light on matters is here to offer assistance. We understand the importance of maintaining proper vehicle functionality and addressing ABS-related issues promptly, and our comprehensive resources are designed to help you navigate and resolve any concerns you may encounter.


Here are questions people also ask about the ABS issue of trailers and their respective answers.

Q: Can I still drive the trailer if the ABS light is on? 

It is not recommended to drive the trailer if the ABS light is on.  There will be limited ABS functionality. This will occur during emergency braking, and maintaining control of the trailer in certain situations could be more challenging.

Q: Can I drive with my ABS module disconnected? 

It is possible to drive without a functional ABS module if conventional brakes are fine. Be cautious in wet conditions as the anti-lock feature won’t work, risking steering loss with tire lock-up.

Q: Is a trailer ABS light a DOT violation? 

If the ABS light is on during a traffic stop, an officer might issue a citation for brake system violation due to the illuminated ABS light. Out-of-service criteria concerning brakes encompass several factors, and one involves the presence of a non-functional ABS.

Final Words

The ABS system is a critical safety feature for trailers, ensuring stability and control during braking. When the ABS light comes on while applying the brakes, it demands immediate attention. Take it to a professional mechanic for fast repair.

Keeping your trailer’s ABS in optimal condition ensures safer travel, protecting your cargo and people on the road. Remember, safety should always be a top priority when towing a trailer, and a well-maintained ABS system plays a vital role in achieving that goal.

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