I did not reinstall the O2 sensor in the R77 since the ECU has been flashed so I had a check engine light. I bought an O2 sensor eliminator on Ebay for $20, you plug it in, ride a little bit, the light goes out. You do not have to purchase one of these, you can keep the light on, or make your own. I believe it is just two 380 ohm resistors on a compatible connector. I went for the $20 purchase instead of monkeying something together by myself.
My first package was stolen by USPS, the bottom of the package was cut the plug was gone. I contacted the seller and he shipped me another one immediately, no question asked. If he was selling something else I didn't want to make myself I'd definitely buy from him again.