Optimizing Subaru ECM

    April 22, 2025
    This bulletin applies to 2015-2019 Subaru Legacy/Outback vehicles equipped with a 3.6L engine and 2015-2020 WRX STI vehicles equipped with a 2.5L engine.
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    Photo courtesy of Subaru
    Subaru offers reprogramming files to optimize the ECM.
    Subaru offers reprogramming files to optimize the ECM.

    This bulletin applies to 2015-2019 Subaru Legacy/Outback vehicles equipped with a 3.6L engine and 2015-2020 WRX STI vehicles equipped with a 2.5L engine.

    Subaru offers reprogramming files to optimize the ECM. The new files will address DTC P0116 and hard starting in cold temperature concerns when an accessory engine block heater is utilized. When the block heater is used, the ECM detects a conflict between the warmed coolant and temperature inputs from other sensors. This causes the ECM to go into a fail-safe mode, resulting in the hard-starting condition due to an improper fuel mixture.

    About the Author

    Mike Mavrigian | Motor Age Editor

    Mike Mavrigian has written thousands of automotive technical magazine articles involving a variety of  specialties, from engine building to wheel alignment, and has authored more than a dozen books that crisscross the automotive spectrum. Mike operates Birchwood Automotive, an Ohio shop that builds custom engines and performs vintage vehicle restorations. The shop also features a professional photo studio to document projects and to create images for articles and books.

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