On my G35 I used a capacitor and a resistor on each 02 sensor to eliminate the codes. It was a 30 minute(including jacking up the car and putting it on stands to remove the 02s), $10 fix buying resistors and capacitors in bulk. I have my rear 02s in the exhaust with race cats. I modified the 02 sensor itself. A 1M ohm 1/4 watt resistor gets soldered in the signal wire between the 02 sensor and PCM. Then on the PCM side of the resistor a 1UF 35V tantalum capacitor gets soldered between the signal wire and signal ground wire. The resistor reduces the voltage peak and the capacitor makes the waveform wider by slowing the voltage rise and fall.