Wiring Harness Replacement
Subaru TSB Link
TSB 07-96-15 - Design Change to Engine Wiring Harness
While not all wiring issues are created equal, the late GR Subarus run into quite a few issues as a result of some questionable engine grounds through the chassis harness. If you're experiencing issues, the age old adage "When in doubt, Ground it out" suggests this may be a good place to start. The cause of this problem is some rather flimsy crimps on the factory harness causing issues with the signal from various sensors and components of your vehicle's engine. This can get exacerbated over time as the engine moves around and puts the harness under stress, which in turn tugs at the harness pulling at these joints causing them to fail. Subaru offers a complete replacement harness as a fix for this issue, but we've found in most cases it's possible to solve these problems rather quickly on your own if you're willing to do a little electrical work. While simple on the surface it's critical that the solder joins are solid so if you aren't familiar with how to solder I would practice on something else before you start to work on your car's harness. Additionally it's not recommended to use crimps like the factory did as they will simply tug right back out again.
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