2013 brz automatic borla header catless down shifting problem from 3rd to 2nd.
 

So over the weekend I installed my catless borla headers on my car and im also running the perrin cat back exhaust. After about an hour to hour and half the check engine light came on because of my setup. Well after that every time coming to a stop it would down shift very hard only from third to second. So I pulled the fuse for the ecu and cleared it and it was gone. Came back again few hours later. I did the same thing over cleared it. While I had just cleared it I made sure it was, I undid the leads for the two sensors for the header and it came back on the spot and had the same down shifting problem from third to second. I guess im hopping someone has an explanation on here for why this is, could it be some type of limp mode?

Do you have a tune? The CEL comes on due to you not having a cat inbetween the two sensors which does throw the car into limp mode. On the other hand, you should have searched it up on the forums. Plenty of threads about the CEL throwing the car into limp mode w/o a tune.

yes, I did actually do some looking but couldn't find anything related and very hard to find because its an automatic. I even asked a handful of people I know that have a very good knowledge about the car. No it is not tuned. The car only does the hard down shift when ether the cel comes on for the cat or if I undo the two sensors.

There's plenty of threads related about headers, cel, and being untuned. Most of them states that the car is thrown into limp mode when you have the CEL from headers w/o a tune. It's just common sense that the harsh downshift is an effect of the CEL since it only happens when CEL is on and that the CEL is the effect of running catless headers w/o a tune. There's also threads about how bad the CEL from headers w/o a tune can be.

I would highly recommend contacting James @ HRI Tuning to get a tune to resolve your issue along with the driveability benefits that come as a result of James work. I did and I couldn't picture having the car any other way.