In Asian vehicles the EPS control unit is mounted separately from the rack. MSG Equipment explains how such racks are diagnosed with the MS561 and MS550.
In Asian vehicles such as Lexus, Mazda, Hyundai, Honda and Toyota, the electric steering control unit is mounted separately from the rack and connected via the vehicle wiring. MSG Equipment notes that this protects the unit from heat swings, vibration and road effects, but makes faults hard to diagnose without special equipment.
Drawing on the experience of Master Service workshops, the article says that in the vast majority of cases the rack must be removed for diagnosis and repair, and only rarely can a scanner alone solve the problem.
The MS561 controller and MS550 adapter connect to the rack via special cables, simulating its connection to the car. As an example, the article discusses common faults of the MA107 rack in the 2010–2013 Mazda 6, such as unequal steering effort to the left and right.