You fire up your truck, do your pre-trip check, and notice the ABS light staring back at you. Maybe it flickered on after you hit a bump, or maybe it’s been glowing for days, either way, you’re wondering - what’s the deal?

You can often diagnose ABS issues by checking fault codes. On your truck, you can access fault codes through the instrument cluster menu by navigating to the “Diagnostics” section (the exact location varies by truck model). Once you have the code, look it up in the manufacturer’s database or a trusted diagnostic database. While a quick internet search might work, it's not always reliable.

For the trailer ABS, checking fault codes is a bit more difficukt but can be done using the blink code method. Since different trailers use ABS systems from different manufacturers, each has its own procedure for accessing blink codes. Below are the general steps for the most common systems:

How to Retrieve Trailer ABS Blink Codes

Wabco ABS

1. Cycle the key on for 5 seconds – The ABS light will illuminate.
   
   

2. Turn the key off – The ABS light will go out.
   
   

3. Turn the key back on – The ABS light will briefly illuminate and then turn off.
   
   

4. Read the blink code – The ABS light will flash the code three times repeatedly.
   
   

Bendix ABS

1. Turn the key on and press/release the brake pedal three times within 15 seconds.
   
   

2. Wait 5 seconds – The ABS light will then start flashing the blink codes for all active faults.
   
   

Haldex ABS

1. Cycle the key on/off twice in 1-second intervals.
   
   

2. Turn the key on and leave it in the ON position.
   
   

3. The ABS light will begin flashing codes, repeating continuously with:
   
   

• A 10-second solid light between cycles
  
  

• A 2-second pause between individual codes
  
  

4. To exit diagnostic mode, turn the key off or disconnect the trailer’s 7-way power cord.
   
   

Look Up the Code

Once you retrieve the blink code, refer to the manufacturer’s fault code chart to determine the issue and recommended fix. Each system—Wabco, Bendix, and Haldex—uses unique blink codes, so ensure you use the correct chart for your system.

What’s Causing Your ABS Light to Stay On?

1. Faulty Wheel Speed Sensors

Your ABS system relies on wheel speed sensors to detect how fast each wheel is rotating, so if one of them is dirty, damaged, or disconnected, the system can’t do its job properly, and the ABS light will stay on.

The Fix: Inspect each wheel speed sensor for dirt buildup or damage. Sometimes, all it takes is a good cleaning to get things back in working order, but if a sensor is completely shot, you’ll have to replace it.

2. Damaged or Corroded Wiring

Big rigs take a beating, and so do their electrical systems. Over time, wires connected to the ABS sensors can get worn, corroded, or even chewed by rodents (yes, it happens), so if the system isn’t getting a proper signal, it will trigger the warning light.

The Fix: Check the wiring harness near the wheel hubs and along the frame for exposed or frayed wires and if you see corrosion, clean it up. If a wire is completely damaged, you’ll need to replace it.

3. Malfunctioning ABS Module

The ABS module is basically the brain of the system. It processes data from the wheel speed sensors and adjusts braking as needed, so if this module fails, your truck will not know when to engage ABS, which is why the light stays on.

The Fix: If you’ve ruled out sensors and wiring, a diagnostic scan tool can check for ABS module errors and in some cases, a software reset will fix it. If not, the module will have to be replaced.

4. Bad ABS Relay or Fuse

Just like any other electrical component, the ABS system has fuses and relays that control power flow, and if there is a blown fuse or bad relay, it can cause the system to malfunction and keep the warning light on.

The Fix: Find your truck’s fuse panel and check for any blown fuses related to the ABS system, and if you find one, replace it with the correct type. It’s also important to test the relay to see if it’s still working well.

Conclusion

Your ABS light isn’t just there for decoration. Your truck will still stop without ABS, but losing it will make a huge difference in an emergency, and you definitely don’t want to experience that.

Did you realize that you need to replace some ABS parts? These may come in handy:

Trailer ABS ECU Unit | Meritor S4461082010
ABS Relay Valve | Meritor S472 500 007 2
7 Way Electrical / ABS Cable ~ 12ft. | Sloan 4CA12 ~ Phillips 30-2051 ~ Tectran 7AAB122MW
3 in 1 ABS Power Cord and Air Hose Assembly - 15ft