Review on Denso 234 9015 Fuel Ratio Sensor by Jay Ngo

Best online price ($99 at the time) for original OE sensor, but connector does not match end on cylinder block side (ie not directly). You should always use the Denso brand for an intake air/fuel O2 sensor, but I assume this is part of the aftermarket and I do not recommend buying Denso sensors from Revain. He cleared the DTC P0030 after connecting all 4 wires after the cylinder block side connector, but it definitely doesn't fit directly and is difficult to work with (hence 2 stars). DIY Tip: You can replace both upstream and downstream sensors. independently on Subaru 2nd Gen (2000-06) models without special tools. (1) Lift and remove the right passenger wheel to gain access to both sensors. (2) Spray the sensor threads with PB Blaster and wait 10-15 minutes. (3) Remove the air intake assembly in the engine compartment and locate the sensor connector, carefully disconnect the connector and lower down. (4) Use a 7/8" or 22mm wrench to unscrew the O2 sensor from the catalyst plug (spray more PB Blaster if it's stuck). (5) Once free, unscrew and remove the sensor and 4 wire harness. (6) Apply anti-seize to the threads of the new sensor and carefully thread it back into the spool to avoid twisting the wiring harness. (7) Remaining installation is in reverse order of removal. CEL will turn off automatically when engine is started without OBD2 reset.