Originally Posted by AtomicAWD

Thanks, so did you install the Tsudo or OEM gaskets on all three originally, then just swapped out on the ones where you got CEL? The Remflex are half the price of Lexus OEM

On at least one of the occasions, the light came on after I was running it bit harder than normal (which is daily-driverish). But I've been doing at least that the past week and the light's still off. Maybe time to give it a good go and see what happens...

Originally Posted by jay90011

Looks like the 02 sensor on the driver side is triggering the check engine light. Have it replaced and you should be good to go. Just be careful installing it this time to avoid damaging the wiring.
Or check to see if the connector is fully pushed in if you disconnected when uninstalling the sensor

Originally Posted by babiibryan

My car is still under warranty. Do you think the warranty is covered it? Or the warranty is voided when I change the midpipe

Originally Posted by jay90011

I have owned and installed 3 tsudo catbacks in my IS's in the last 10 years and can tell you that only two issues could come up when getting a check engine light after install.
1. Gasket leak at the catalytic converter connection where the catback connects to. The leak wont appear when revving at the shop or at a stand still but will leak at or above 25mph. Symptoms of the gasket leaking will cause check engine light to stay lit and will not go away.
The resolution is to buy these gaskets below. They solved my issue on the last two catbacks I installed.
Remflex 6005 Exhaust Collector Gasket

2. When removing or installing O2 sensors the wiring was twisted or pinched to the point where the O2 sensor is no longer providing a constant current back to the Ecu. Symptoms will cause check engine light to appear for a bit and will go away. You may see the check engine light flicker on rainy days.
Resolution would be to change out the O2 sensor that is damaged.