The Denso O2 Sensor for the 12-15 Civic Si is a great alternative to the factory unit. Designed as a replacement for the OE Part Number 36531-RX0-A01, this primary O2 sensor will work with most aftermarket headers and factory exhaust systems. Please note you may need to run a defouler in order for the O2 sensor to read correctly when used with an aftermarket header.