Application Notes for Aisin AW4

The COMPUSHIFT Sport and COMPUSHIFT Pro support the Aisin AW4 transmission. This transmission was made in many different versions, but for our purposes, there are two major types that have different ratios, speed sensors, and connectors. HGM refers to these as the “early” and “late” models, and aside from a different main connector, the two transmissions have different overdrive ratios, with the early one having 0.705:1, and the later having 0.750:1. While there are different output shaft pulse counts, these can be adjusted in software.

Possibly the most comprehensive discussion is available here: https://www.naxja.org/forum/showthread.php?t=1053970

AW4 vs. A340

As compared to the Toyota A340, the AW4 has one significant difference the valve body: the manual valve does not have a 1st gear position. Most A340’s use an overdrive cancel switch with lever positions of P,R,N,D4,D2,D1, with the D4 position being converted to D3 when the overdrive cancel is selected. On the AW4, the positions are P,R,N,D4,D3,D2, and no first gear hold is available by default.

Using AW4 with a COMPUSHIFT Controller

The AW4 originally came with a shift selector switch that could decode the Park position. Moreover, the D4 position on the switch was all circuits open, which meant that when the switched failed, the transmission always indicated D4. HGM has opted to not use the original switch and instead provides a Toyota A340 style switch with each harness. The COMPUSHIFT controller provides outputs to drive a reverse relay and neutral start relay so those functions can be used without tapping into the lever switch.

Wires in the harness that are normally dedicated to an overdrive cancel switch and overdrive cancel LED are repurposed to a 1st gear hold switch. This switch must be connected as a momentary pushbutton. With the shift lever in the D2 position, the button can be pressed once to lock in 1st gear, and pressed again to resume 1-2 shifting operation. The LED will light when the 1st gear hold is active. Moving the shift lever will cancel this function as well.