What is aux in a truck?
Aux means auxiliary—the extra systems beyond the main engine, typically the auxiliary power unit (APU) and related electrical or hydraulic functions that run when the engine isn't running or to support accessories.
What does 'aux' refer to in trucking?
In the trucking world, 'aux' is shorthand for auxiliary. It covers the power, air, or control circuits that are not part of the core propulsion but are essential for comfort, safety, and productivity. The exact implementation varies by truck make, model, and fleet, but the concept is constant: auxiliary systems extend the truck’s capabilities beyond simply moving from one place to another.
Common uses of auxiliary (AUX) systems on trucks
Below are the typical ways fleets and drivers rely on aux capabilities to operate smoothly, save fuel, and stay comfortable on long hauls.
- Auxiliary Power Unit (APU): a compact power package that provides electrical power and climate control for the cab and sleeper when the main engine is off.
- Auxiliary electrical power/inverter: converts DC from the truck battery to AC to run appliances or to power trailer controls when needed.
- PTO-driven hydraulic or pneumatic systems: powers equipment such as liftgates, cranes, winches, or other secondary systems on the body or trailer.
- Auxiliary lighting and accessories: additional cab or exterior lighting, power outlets, USB ports, and other conveniences that don’t require engine operation.
- Auxiliary climate control and hotel load management: separate circuits or controls that keep the cab comfortable during rest periods and long stops.
These auxiliary systems help fleets improve driver comfort, protect cargo, and reduce engine idling, contributing to better fuel efficiency and lower wear on the powertrain.
Where you’ll see the AUX label on a truck
As trucks incorporate more electronic features, you’ll encounter the AUX label in several common places, indicating optional or supplemental function.
- Dashboard or control console: an AUX switch or button that powers aftermarket equipment, inverter, or the APU when needed.
- Instrument panel: indicators or gauges labeled AUX that show status of auxiliary power or circuits.
- Trailer and reefer interfaces: AUX controls for trailer power, refrigeration unit, or auxiliary lighting on the trailer.
- Electrical connectors and outlets: AUX-labeled circuits in 12V/24V or 110V outlets for accessories and fleet devices.
Being aware of where AUX appears helps drivers manage consumption, avoid overloading circuits, and ensure that essential equipment is available when required.
Best practices for managing auxiliary systems
To keep aux systems reliable and efficient, follow these practical steps.
- Identify which auxiliary systems you’re using (APU, inverter, PTO-powered hydraulics) and understand their power requirements.
- Monitor battery and fuel levels; avoid running the APU or high-demand loads when battery voltage is low or fuel is scarce.
- Perform regular maintenance on APUs and auxiliary components per the manufacturer’s schedule to prevent unexpected downtime.
- Use upgrades or fleet settings to optimize idle decisions: prefer shore power or an APU where available, and shut down auxiliaries when not needed.
- Practice safety: disengage heavy loads, follow lockout/tagout procedures when servicing auxiliary equipment, and keep clear of moving parts during operation.
Adopting these practices helps drivers extend equipment life, protect cargo, and reduce operating costs across long-haul and regional routes.
Why auxiliary systems matter for modern trucking
As fleets transition toward more electrified and efficient operations, auxiliary power is increasingly central. APUs reduce engine idling, support sleeper cabin comforts, and enable refrigeration and other services without idling. In electric and hybrid trucks, the line between aux and core propulsion blurs, with robust energy management and battery systems handling both motion and auxiliary loads.
Summary
In trucking, aux is shorthand for auxiliary—the extra power, air, and control systems that run alongside the engine. From APUs that keep cabs warm or cool to inverters powering accessories and PTO-driven hydraulics for trailers, auxiliary systems extend capability, improve efficiency, and enhance safety. Understanding where 'AUX' appears and how to manage these resources helps drivers and fleets operate more reliably on the road.
