A check engine light may illuminate if you install a de-cat exhaust or a high-flow sports catalytic converter on your car. This is usually because a sensor in the exhaust system detects an issue with catalytic converter and interprets it as a failure, causing the check engine light to illuminate.
This oxygen sensor extension known as a MIL (malfunction indicator lamp, also known as the check engine light) cheater elbow may solve the issue, but it is suggested that the vehicle be remapped to ensure that the problem is addressed properly.
Without an oxygen sensor elbow the sensor detects an increase in CO2 readings as a result of the increased gas flow and flags it as a malfunction, causing one of the warning lights on the dashboard to illuminate.
This lambda sensor extension will help in overcoming this problem by removing the sensor from direct gas flow, misleading it into reading that exhaust gas levels have not risen. This MIL cheater elbow prevents the check engine light from coming on.
According to anecdotal reports, using an oxygen sensor elbow works sometimes but not all the time. It's often used with a sports cat, which may also sometimes trigger the check engine light.
If you install the decat exhaust, it is usually suggested that you have the vehicle remapped as well as install a MIL cheater oxygen sensor elbow otherwise the check engine light will be activated.