← Tech

Aisin AW-4 automatic (4-speed)

The 4-speed automatic that takes anything

Behind the 4.0, the Cherokee's go-to automatic was the Aisin AW-4: four speeds, with overdrive and a lockup torque converter. It has a reputation for being nearly unbreakable, and it's one of the reasons an automatic XJ ages so gracefully.

Japanese blood

The AW-4 was built by Aisin-Warner (Aisin AW), the same Japanese house behind a lot of Toyota automatics; it's in fact a close relative of the Toyota A340. It's an electronically controlled unit: a computer (TCU) handles shifting and torque-converter lockup.

That origin gave it uncommon toughness for its class and era. It handles considerably more torque than the 4.0 makes stock, which is why it's so sought after even for swaps into other projects.

Practical notes

It works hand in hand with the NP231 and NP242 transfer cases. If the TCU detects a problem it drops into 'limp mode' (a single gear) so you can limp to the shop without hurting it. Key maintenance is simple: fluid and filter on schedule, and good cooling if you run it loaded or off-road.

Its ratios (2.80 / 1.53 / 1.00 / 0.75) pair a short first for launching with a tall overdrive for the highway — another reason why, on big tires, you'll want to sort out the axle ratio. One compatibility note: early AW-4s (through ~1990) used a 21-spline output shaft and a 0.705 overdrive; from 1991, with the 4.0 High Output, they moved to 23 splines and 0.75.

A340 family and compatibility

The AW-4 didn't fall from the sky: it belongs to the Toyota A340 family (built by Aisin-Warner, part of the Toyota group). Its ratios are essentially those of the A340E and it shares parts with the Aisin 450-43LE from Toyota off-roaders. It's in fact the first electronically controlled A340 fitted to a North American chassis —hence its unbreakable reputation: it's 1980s Japanese automatic tech bolted under a Jeep. The Toyota/Lexus units in the family (Supra, 4Runner, Cressida, LS400) serve as donors for some internal parts, though they're not a direct bolt-in.

For swaps, the key point is the removable bellhousing. Behind the 4.0 it uses the AMC straight-six pattern; behind the 2.5, the GM 2.8 V6 pattern —two different bellhousings that don't cross over. Within Jeep the AW-4 ran in the XJ (1987–2001), the MJ Comanche (1987–92) and the Grand Cherokee ZJ, but only in 1993. And if you're going to work on it, remember: it's electronically controlled, so a lot of faults are the throttle sensor (TPS) or the computer (TCU) rather than the transmission itself.

Specifications