I just recently installed a borla exhaust a few weeks ago and today the cel light came on. So i scanned the car and the code that comes up is P4030 the catalyst system efficiency is below the required threshold. So my question is this normal?

 

I didn't have any error codes with my Borla exhaust.

Check and make sure the O2 sensors are connected correctly and screwed into the new Borla correctly.....

 

A fairly well-known problem I think. The error code is probably P0430 (not P4030). It occurs with me with my Borla very infrequently. Others never get this error. The current thinking (endorsed by RR Racing) is that Borla should have included new exhaust gaskets. I put in new ones just last week and I hope that fixes it. Part number is 90917-06070. About $30 shipped.

 

new gaskets is what is required. sometimes incorrectly installed gasket will cause the issue..... make sure they are not pinched when installed.

 

i have header back and the 90 degree 02 elbows installed on the SECONDARY 02s and i occaisionally get that code . just clear it you will be fine if it pops up everyday after clearing you have a problem. Brand new exhaust systems will trigger it a few times or not at all cause the car is getting used to the additional flow

 

Pretty doubtful on the increased flow theory. The O2 sensors are unhappy. Leak sounds like the most likely cause for sure. Lexus uses a fairly complex test for catalyst efficiency and a leak will definitely make it fail.