---
slug: semi-trailer-maintenance
title: "Semi Trailer Maintenance: The Trailer's Systems"
description: "A semi trailer has its own systems to maintain, separate from the tractor: brakes and ABS, wheel ends, tires, suspension, landing gear, and lighting."
track: maintenance
kind: article
isRegulatoryAdjacent: false
publishedAt: 2026-10-19
updatedAt: 2026-10-22
source: https://shopbluecollarparts.com/kb/semi-trailer-maintenance
license: CC BY 4.0
---

# Semi Trailer Maintenance: The Trailer's Systems

A semi trailer carries its own set of systems to maintain, separate from the tractor that pulls it. A tractor and trailer share the road and share the air brake system, but the trailer has its own brakes, its own wheel ends, its own suspension, and its own lights — and they wear and fail on their own schedule, not the tractor's. This page is the map of the trailer's systems for a service provider. Each section links to a page that goes deeper.

## What does semi trailer maintenance cover?

A trailer maintenance visit is usually grouped into these systems.

1. **Brakes and ABS.** The trailer's half of the [air brake system](/kb/air-brake-system) — supply and emergency lines, the relay-emergency valve, spring brakes, slack adjusters — plus the trailer's own antilock brake module. See [trailer brake adjustment](/kb/trailer-brake-adjustment) and [trailer ABS troubleshooting](/kb/trailer-abs-module).
2. **Wheel ends.** The hubs, bearings and seals that carry the trailer's weight and let the wheels turn freely. See [trailer wheel end maintenance](/kb/trailer-wheel-end-maintenance).
3. **Tires and the tire inflation system.** Trailer tires carry load without an engine to signal a problem through the drivetrain, which is why many trailers add a tire inflation system that keeps the tires at their set pressure or flags one that's low. At this level, the system is: tires, the wheel valve or hose that feeds each one, and a controller or gauge that reports pressure or flow. Where a trailer has an inflation system, its condition is usually recorded with the tire and wheel work. See [semi truck and trailer tires](/kb/semi-truck-and-trailer-tires) for the tire and wheel system, and [trailer tire inflation systems](/kb/semi-truck-tire-pressure-and-inflation) for how the inflation system works.
4. **Suspension.** On most semi trailers, an air-ride suspension with air springs, a height control valve, shocks and pivot bushings. See [trailer air ride suspension](/kb/trailer-air-ride-suspension).
5. **Landing gear.** The legs that support the trailer when it's uncoupled, and the gearbox and crank that raise and lower them. See [trailer landing gear repair](/kb/trailer-landing-gear-repair).
6. **Lighting and the 7-way connector.** The trailer's marker, clearance, turn and brake lights, and the connector that carries power and signals from the tractor. See [semi trailer lighting and wiring](/kb/semi-trailer-lighting-and-wiring).

## Why the trailer gets its own maintenance record

A tractor and trailer are often serviced on different schedules, by different service providers, and sometimes for different customers. A trailer-specific record keeps the trailer's own history — by VIN or unit number — intact no matter which tractor pulled it that week, or which service provider saw it last.

## Use the manufacturer's documentation

Trailer hardware differs by manufacturer and by component: an axle maker's wheel-end documentation, a suspension maker's ride-height specification, an ABS maker's diagnostic procedure. This page is a map of what to maintain, not a service manual for any one trailer.

## Log the work in Blue Collar Parts

A technician who services a trailer can log the work in Blue Collar Parts and send the record to their customer, who confirms it. [Learn what Blue Collar Parts is](/kb/what-is-blue-collar-parts).

---

*This page describes semi trailer systems in general terms. It is not a service manual and does not establish regulatory compliance. Use the equipment manufacturer's current service documentation for equipment-specific procedures.*

## Sources

What BCP does here: Blue Collar Parts records the work and sends the report to your customer. It does not perform, certify or approve inspections.
Reviewed 2026-10-22