Onboard Air and Selectable Lockers for Tacoma, 4Runner, ZR2 and JK

Airing down is the cheapest traction upgrade there is, and airing back up is what stops people doing it. A tire at trail pressure is unsafe on the highway, and a gas station compressor at the end of a long forest road is rarely there. An onboard compressor solves that, and once it is fitted it opens the door to the second upgrade in this guide: an air-actuated locking differential. The two are sold separately and are best planned together.

The first decision is portable or mounted. A portable compressor lives in a bag, clamps to the battery, and moves between vehicles. It suits an owner with more than one machine or a daily driver with limited space. A mounted compressor bolts under the hood or in the bed, is wired permanently, and can feed an air tank and a locker. It suits a dedicated trail vehicle. Either way, the pressure you inflate to depends on the tire, wheel and load; the values are in your tire and vehicle documentation and we do not publish them.

Under-hood space decides where a mounted compressor goes. The Toyota Tacoma (N300, 2016–2026) and 4Runner (N280, 2010–2026) have room on the passenger side inner fender on most engines; the Jeep Wrangler JK (JK, 2007–2018) and Wrangler JL (JL, 2018–2026) have a crowded bay and many owners use a bracket on the firewall or a bed or cargo-area mount. The Colorado ZR2 (ZR2, 2017–2026) engine bay varies by engine; check the space on your own truck before ordering a bracket. A compressor near the exhaust or the turbo overheats; a compressor mounted low fills with water at a crossing. Both are common mistakes.

Wiring is the part that is done badly most often. A compressor draws heavy current for minutes at a time, and it must be fed through a relay on its own fused circuit from the battery, with a cable gauge sized for the run length. The manufacturer's instructions give the gauge and fuse; follow them rather than reusing whatever is in the toolbox. Route the cable away from the exhaust and secure it so it cannot chafe on a sharp edge, which is the same lesson the recall record teaches about fuel lines and harnesses on these platforms.

A locking differential forces both wheels on an axle to turn at the same speed, which means a wheel in the air or on ice cannot take all the drive. An open differential does the opposite. A limited-slip sits between the two. Several off-road trims across the vehicles in our list ship with a factory locker on one or both axles; check your build sheet or owner's manual before buying another.

An aftermarket selectable locker is for the vehicle that does not have one, or that has a rear and wants a front. The ARB Air Locker is listed in our parts records for the N300 and, in a second listing, for JK, N280 and ZR2, described as a selectable air-actuated differential lock for slow technical terrain. Our records note that it requires a compressor, which is the reason this guide pairs the two. The locker replaces the differential carrier, so it is a job that involves setting up ring and pinion contact, and it is also the natural time to change the axle ratio if bigger tires are planned.

An air locker needs a clean, dry air supply and a small solenoid on the dash. The compressor that airs up tires can supply the locker, but a locker that leaks at the seal will run the compressor constantly and drain the battery. A dedicated small compressor for the locker plus a larger one for the tires is the belt-and-suspenders approach; a single compressor with a tank and a pressure switch is the common one. Run the air line where a rock cannot pinch it; a crushed line at the axle is the usual failure.

Lockers change how a vehicle steers. With a front locker engaged, the vehicle wants to go straight, and turning on a tight rock ledge becomes a matter of engaging it for the climb and disengaging it for the turn. With a rear locker engaged on a side slope, the vehicle can push its tail downhill. None of this is dangerous once understood, and all of it is surprising the first time. Practice on an easy trail.

Water crossings are where lockers and compressors both suffer. Our repairs database logs rear differential and axle seal leaks after wading against N300, N280 and JK, and a diff that has taken on water will emulsify its oil without any outward sign. The maintenance schedule for trucks and SUVs calls for a differential fluid check every fifteen thousand miles for exactly that reason; after a season of crossings, check sooner. An air locker adds seals to that differential and the same rule applies. The fluid capacity and the specification are in your service manual.

The order most owners settle on is compressor first, used for a season to see how much airing down actually changes, then a rear locker if the vehicle lacks one, then a front locker only if the terrain demands it. A compressor alone, paired with an all-terrain tire in the size the vehicle was built for, will get a stock 4Runner or Tacoma up most trails in the Desert Southwest and the Sierra. The locker is for the last few obstacles, and the regearing that often accompanies it is a separate guide.