ECU problems
 

Yesterday my 2013 BRZ went into limp home mode just after driving onto the freeway. All the systems warning lights came on, it lost P/S, ABS, Traction, and CEL came on. Car also would not exceed 4K rpm. The car has an Ecutek tune, with 91, 100 & E85 tunes on it. I tried to reinstall the tune but could not communicate with the ECU.
Several hours earlier in the day I had removed and then reinstalled a racing battery, but experienced no problems with the installation or running of the car until this incident. The car has about 30K on it and is used regularly as a DD and to autocross.

I took it into a Subaru Dealer who has not found the problem yet. Anyone else experienced a similar problem?

You weren't able to pull any codes using the Ecutek cable? That's quite a communication loss if the ECU shut off everything but the engine was still able to run. I'd say put the old battery back to rule it out. It is an electrical component and this big of a control system fault would make me point the finger at the only electrical component that's changed. I doubt all of those things failed simultaneously.

Good point, I was thinking along the same lines. I'll take the regular battery to the dealer and install it. thanks

Dogged a bullet on this one. Turns out there is an inline fuse on the battery cable that blew! I didn't even know there was a in line fuse on the cables. Dealer had the car over 2 days and it ill take several days to order, but happy I'm not replacing the ECU!

Dont count your chickens yet.

That fuse ( or likely fusable link) blew for a reason, if the car ran fine for a period after installing the battery it may not be the battery.

They may find when they install the new "fuse" it blows again, as their may be an electrical fault\short somewhere.

The alternators in these cars are controlled by ecu, its possible that the "racing" battery may have caused a situation where the battery overcharged or overloaded alternator but unlikely.

will be interesting to see if their is another fault other than fuse


The ecu is likely ok as it was still running in limp mode, if the ecu died car would stop dead, limp mode is generally entered when ecu detects abnormal sensor readings or conditions