4005001120 | Genuine Wabco ABS Trailer ECU Valve Assembly

An ABS Trailer ECU Valve Assembly 4005001120 is the brain and control valve of the trailer’s anti-lock brake system, helping the trailer stop safely without skidding. ABS Trailer ECU Valve Assembly

General Specifications

Fitment

• Great Dane trailers
• Stoughton trailers 
• Utility Trailer
• Vanguard trailers
• Wabash National 
• Manac 
• Freightliner 
• International/Navistar 
• Kenworth 
• Peterbilt 
• Mack 
• Volvo 

Specifications

• Calculated Volume (dm³)

  6.24

• Max. operating pressure

  13.0 bar

• Port thread 1

  2x 3/4 - 14 Dry Seal NPTF

• Port thread 2

  4x 3/8-18 Dry Seal NPTF

• Port thread 3

  Flap exhaust

• Port thread 4

  3/8" - 18 Dry Seal NPTF

• Product category

  Device

• Protection class

  IP 66

• System

  2S/1M MSH

• Technical specification

  OE specification

• Temperature range

  -40°C to +65°C

• Type

  TCS II Basic

• Voltage

  12 V

Purpose & Function

1. Prevent Wheel Lockup

During hard braking:

• The ECU detects if a wheel is about to stop rotating.

• The valve rapidly adjusts air pressure to that wheel.

This prevents skidding.

2. Improve Trailer Stability

It helps:

• Prevent trailer swing

• Reduce risk of jackknifing

• Keep the trailer tracking straight behind the tractor

3. Maintain Steering & Control

Even though the trailer doesn’t steer, preventing lockup:

• Keeps the trailer stable

• Prevents loss of directional control

• Reduces loss of traction on wet or icy roads

4. Reduce Tire Wear

Locked wheels cause:

• Flat spots

• Rapid tire damage

ABS prevents that by keeping wheels rotating during braking.

5. Meet Legal Requirements

In many countries, including the U.S., ABS has been required on most air-brake trailers since the late 1990s.

Signs of a Bad

1. ABS Warning Light Stays On

• Trailer ABS light stays illuminated on the trailer

• ABS warning stays on in the tractor dash

This is the most common symptom.

2. Wheels Lock Up During Hard Braking

If ABS is not functioning:

• Trailer wheels may skid

• You may see flat spots on tires

• Trailer may feel unstable under heavy braking

3. No ABS Self-Check Click

When you first power the trailer (key on), you should often hear:

• A brief clicking or cycling sound from the ABS valve

If there’s no sound, the valve may not be activating.

4. Air Leaks from the Valve

A failing modulator valve may:

• Leak air constantly

• Leak only during brake application

• Leak from exhaust ports

Air leaks can reduce braking performance.

5. Intermittent ABS Operation

• ABS light turns on and off

• Braking feels inconsistent

• Fault appears only during wet conditions

Could indicate internal valve or ECU failure.

6. Fault Codes (Most Accurate Method)

Using a diagnostic tool, you may see:

• Modulator valve faults

• ECU internal failure codes

• Power/ground communication faults

This is the most reliable way to confirm failure.

7. Poor Trailer Stability During Braking

• Trailer pulls to one side

• Feels like brakes are grabbing unevenly

• Increased risk of trailer swing

About International / Navistar

International, a brand of Navistar International Corporation, is a leading American manufacturer of commercial trucks, buses, and diesel engines. With a history dating back to the early 1900s, International is known for producing durable and reliable vehicles used in freight, construction, and municipal operations.

Navistar has built a strong reputation in the trucking industry by focusing on innovation, performance, and long-term dependability. Their vehicles and components are trusted by fleets and drivers across North America and beyond.