Understanding ABS Warning Lights on Trucks and Trailers

Decker 24 Truck and Trailer • November 17, 2025

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Yellow oversized semi-truck parked in a lot under a bright blue sky.

Introduction

Modern commercial trucks and trailers are equipped with Anti-lock Braking Systems (ABS) to enhance safety during emergency braking and slippery road conditions. These systems help prevent wheel lock-up and maintain steering control, which can be life-saving during evasive maneuvers. But when an ABS warning light comes on, it can be confusing or even alarming for drivers. What does the light mean? Is the vehicle safe to drive? And how should it be addressed?


At Decker 24 HR Truck & Trailer, we specialize in diagnosing and repairing ABS issues quickly and accurately. This blog will help you understand what ABS lights indicate, why they come on, and how to resolve them to stay safe and DOT-compliant.

What Is an ABS Warning Light?

The ABS warning light is a dashboard indicator that alerts you to a malfunction in your truck or trailer’s anti-lock braking system. When everything is working properly, the light comes on briefly during startup and then turns off. If it stays on or illuminates while driving, there is a problem that requires attention.


Common Causes of ABS Lights on Trucks and Trailers

1. Faulty Wheel Speed Sensors

These sensors detect how fast each wheel is rotating. If one fails or provides erratic readings, the ABS system may disable itself and trigger a warning.

2. Damaged Wiring or Connectors

ABS systems rely on electrical connections from the sensors to the ABS control module. Corroded, loose, or damaged wires can lead to communication errors.

3. Faulty ABS Module

The control unit that processes wheel data and activates ABS may fail due to age, heat, or internal errors.

4. Low Battery Voltage

If the truck experiences low voltage, it may cause the ABS system to malfunction or log false fault codes.

5. Trailer ABS Communication Issues

For trucks pulling trailers, a separate ABS system is installed on the trailer. If the trailer ABS light is on, it could mean the truck and trailer aren’t communicating properly or a fault exists in the trailer's system.


Is It Safe to Drive with the ABS Light On?

Generally, yes — the truck or trailer can still be driven because the service brakes still function. However:

  • ABS will be disabled, which affects control in emergency braking
  • The vehicle may fail a DOT inspection
  • Ongoing issues may lead to more expensive repairs if ignored


How to Diagnose ABS Light Issues

At Decker 24 HR Truck & Trailer, we follow a thorough diagnosis process:

  1. Pull Fault Codes using a compatible ABS scanner
  2. Test Wheel Speed Sensors for signal accuracy
  3. Inspect Wiring Harnesses and Connectors for corrosion or breaks
  4. Check Power and Ground Supply to the ABS module
  5. Evaluate the ABS Controller if all sensors check out

Our technicians are trained to work on Bendix, WABCO, Haldex, Meritor, and other common ABS systems found in trucks and trailers.

Preventing ABS Problems

Inspect wiring regularly, especially at the wheel ends

• Keep ABS tone rings clean and free of debris

• Avoid using high-pressure washers near electrical connectors

• Schedule regular PMs with ABS diagnostics


ABS and DOT Compliance

A lit ABS warning light is considered a defect during a DOT inspection. Even though it's not always an out-of-service violation, inspectors will note it, and repeated violations can impact your CSA score.

 

ABS Light on Your Trailer?

If the ABS light on your trailer is on:

  • Check the 7-way electrical connection to the tractor
  • Inspect trailer wheel sensors and wiring
  • Look for ABS blink codes on the trailer ABS lamp

 

How Decker 24 HR Can Help

  • 24/7 mobile ABS diagnostics and repair
  • In-shop service for major repairs
  • Technicians trained on truck and trailer ABS systems
  • Service for Amazon Relay, FedEx, JB Hunt, Dayton Freight, and more

We keep sensors, wiring harnesses, and control modules in stock for fast turnarounds.

 

Conclusion

An ABS warning light is more than just a nuisance — it's a sign that your truck or trailer’s most advanced braking system isn’t functioning as intended. Whether it’s a simple sensor issue or a more complex module failure, Decker 24 HR Truck & Trailer has the tools and expertise to fix it quickly.

Don’t risk a failed inspection or unsafe brake performance.

📞 Call us anytime for mobile or in-shop ABS diagnostics and repairs.
🌐 
www.Decker24HR.com

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