When an aftermarket high-flow catalytic converter is used on a late model car its common to see a CEL (Check Engine Light) come and go. This CEL is usually backed by a fault code that indicates a failed cat. If your new cat is NEW, how could it have failed? Behind the scenes, the factory ECU is comparing the readings from a pair of oxygen sensors to measure the effectiveness of the cat. When a high-flow cat is used the exhaust gases are able to pass by the cat at a much faster rate, disrupting the readings. Our o2 sensor spacer retracts the second oxygen sensor from the direct flow of gases, restoring the balance that the ECU requires when using a high-flow cat. Our O2 Sensor Spacer is CNC machined from cold roll steel & grade 8.8 metric hardware. After assembly, our spacer undergoes a zinc dichromate plating process which protects the spacer from corrosion. Installation is plug & play. Simply thread in our spacer, thread in the rear o2 sensor, and lock the spacer at the desired angle. Strictly for use with a 49 state legal aftermarket high-flow catalytic converter such as the Magnaflow catalytic converter used exclusively in our exhaust systems. This product is not intended to and will not provide emissions compliance. Emissions laws vary by state. Check local and federal laws before modifying your exhaust system. Emissions compliance is the sole responsibility of the vehicles owner.