Quick Fix: Subaru GR TSB 07-96-15

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.

Applicable Model/Year:

2012-14 WRX Models (EXCEPT STI)
2012-13 Forester Turbo

Tools Required:

Flat blade screwdriver
Wire Cutters
Razor Blade/Exact0 Knife (optional)
Soldering Iron
Solder
Heat Shrink
Super 88 Electrical Tape

Steps to Fix:

Locate the engine harness on the passenger's side of the car (USDM)
Remove the electrical tape covering the harness either by unwinding or by carefully cutting it off of the corrugated tubing.
Remove the corrugated turbing and save it for later on.
Remove the next layer of electrical tape to fully expose the wires.
Find the three different grounds, they're all covered with large balls of electrical tape. There will be a set with multiple black and yellow striped wires going in to one. The other two sets of ground will be a single wire going into another wire but the ball of tape gets pretty large and one will likely have an exposed wire hanging out underneath. While it may be good to do the power wires that are also crimped, a failure of those wires will result in a problem you always have unlike the grounds which are typically inconsistent issues.
Remove the electrical tape and the sticky goo covering the connector.
Do you best to clean off the goo using some
With the wire joint exposed you can now see the connection for the grounds, these are what we need to replace.
Cut out just the exposed wiring, and trim the wire back. Be careful not to make these too short or you may need to add more wire to prevent the harness from getting stressed
Cut some heat shrink to fit and slip it over the wire away from the joint.
Solder the connection between the wires.
Repeat with the other two sets of grounds.
With everything soldered, go ahead and pull up the heat shrink tubing and shrink it downto seal up the connections.
Loosely spiral the electrical tape around the harness, this keeps everything together.
Install the corrugated plastic wire covering in order to reduce the potential for abrasions.
Now thoroughly cover the entire harness with a continuous piece of electrical tape, but leave about an inch exposed leading up to the connector so the wires aren't stressed and pulling on the pins.
Remove the bracket by putting a screwdriver in the tab and sliding it out towards the engine.
remove the bracket or zip tie it to a lower part of the harness
Zip tie the connector to your brake line or something else. Since the wires got shorter by being cut and re-soldered this can lead to a bit more stretching and tugging as the engine shifts. By moving this forward you gain a bit more room for the engine to move without pulling on the wire.