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Introduction

With the exception of boost control, the Ascent ECU generally shares the same logic as the DIT WRX ECU (FA20DIT motor) with only minor differences. Boost control code is entirely new on the Ascent due to the introduction of a fully electronic wastegate valve and air bypass valve on its FA24DIT motor. Subaru advertises the Ascent CVT transmission as a "high torque" unit, but some owners of stock vehicles are reporting transmission failures on the stock tune. Tuning your vehicle voids your powertrain warranty. Tuning products are to be used at your own risk, so consider carefully before proceeding.

Boost Control

The general behavior of the new boost control logic for the FA24DIT motor is similar to the FA20DIT logic. Instead of determining a commanded wastegate duty, the new logic determines a commanded wastegate shaft position. It uses a boost targets table with baro and IAT comps, proportional/integral (PI) loop based on boost error ("turbo dynamics"), and an initial wastegate position table also with baro and IAT comps. Additionally, there are new DTCs pertaining to boost control and new tables for controlling the air bypass valve state.

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