Engine light stays on, flow master exhaust was installed earlier, do l need to modify oxygen censor on engine side of catylitic converter?
Your probably right about the O2 sensors. Depending on the vehicle, they sell MIL eliminators that plug into the o2 sensor wiring.
A flow master system should not affect O2 operation unless you eliminated the O2 sensor BEHIND the catalytic converter. If you did then you need the above. If both are still there one of them happen to go bad. Get them tested by you local emmission certified garage. Good Luck