Removing the Y pipe and converting your truck's current "single" exhaust system into a "dual" system will cause a smog check failure.
The smog technician will consider the modification you've made as a "tamper". You must keep the original exhaust system configuration designed by your vehicle's manufacturer. Even when converting to a dual system and adding a second catalytic converter lowers emissions, the fact that the conversion is not factory will cause the vehicle to fail the smog inspection.
