Volvo FH4/FM4 EBS Trailer Brake Modulator 21114977 K028781 23166657 24V Used

Description:
This listing is for a used genuine Volvo / Knorr-Bremse EBS trailer brake modulator valve, designed for modern electronic braking systems on heavy commercial vehicles. The unit is clearly marked with Volvo part number 21114977 and Knorr-Bremse number K028781, matching OE listings for the trailer brake pressure control / EBS modulator used on Volvo FH4, FM4 and FMX Euro 6 trucks, and as a service replacement for earlier FH/FM/NH 9–16 series models.

The modulator controls air pressure supply to the trailer or semi-trailer brakes under command of the EBS/ABS system, improving braking stability and response. It combines a multi-port pneumatic valve block with an integrated 24V electronic control unit and is usually chassis mounted near the rear axle group. Multiple independent sources confirm cross-reference numbers 23166657, 23166658, 7423166658, 7421327354 and 21327354 for this application. 

Compatibility (reference only – match part number and photos):
- Volvo FH4 / FM4 / FMX-4 series (from approx. 2013-, Euro 6) with EBS trailer brake system.
- Also listed as suitable for Volvo FH, FM, FMX, NH 9/10/11/12/13/16 and certain North American VNL models using the same EBS trailer control valve. ([tbtparts.com](https://www.tbtparts.com/modulator-23166657-p-6044.html?utm_source=openai))
Always confirm compatibility by checking your existing part number (21114977 or any of the reference numbers above) and connector/port layout before purchase.

This part was tested on the donor truck before dismantling: the EBS system reported no active faults and trailer braking operated correctly. After removal the modulator was visually inspected; no cracks, broken ports or connector damage were found. Condition is graded B – used, fully functional with normal cosmetic wear, oxidation on fasteners and light surface dirt from service. The item is supplied as the complete modulator with electronic module only; mounting bolts, brackets, gaskets and air pipes are not included unless shown in the photos.

Professional installation is strongly recommended. After fitting, the vehicle EBS system should be checked for leaks and fault codes, and calibrated/programmed with suitable diagnostic equipment if required by the vehicle manufacturer procedures.

Shipping & Returns:
We ship across UK/EU with tracked services. Returns accepted within 30 days; buyer pays return postage. Please inspect upon arrival and message us with any concerns.

Why Buy From Us:
Genuine part, 3-month warranty, fast dispatch, secure packaging.