oxygen sensor

When you initially scanned the car to see it had a O2 sensor code what was code? If it was heater circuit related check that with ignition key on one of the 4 wires at the sensor electrical connector should have 12 volts with the connector disconnected if not check the fuses. Did you replace the right O2 sensor the fault code should have distinguished B1S1 or B1S2.

If that was why the lite was on,and you believe the problem is now resolved,you can disconnect your negative battery cable.Keep in mind,if you have the factory radio in the car,you will need the radio code to power up the radio once battery cable is reconnected..Flex

Well, since the Check Engine light is still on WILL stay on UNTIL you get it looked at again. I would take it to a reputable national chain, such as Midas or NTB, who can do it for between FREE to $100 for a FULL diagnostic test. With Midas, they will charge you close to $800 for a catalytic converter, which is the going rate. And with labor and parts will run you close to $900 without tax included. NTB will charge you about $300 more at around $1,200 for to replace the catalytic converter. DO NOT take it to your dealership at all. You can have them do the full diagnostic test to tell you what is wrong with it. But if they charge you a lot of money for it, ask them before they do the job to tell you as to why they do it, and before you sign off on it, take a look at the parts or whatever is bad, so you can have a feel as to why the price to get it done is there. The dealership will "rob you blind" on this major part of the vehicle. So beware of them. That was why I checked with them first to get the first diagnostic done. But in your case, since you get the sensor done, that is good. But I am afraid that you got the same code of P0420. But get a 2nd opinion to make sure it is that code. If it is the P0420 code, then it is the catalytic converter and that NEEDS to be replaced ASAP. Do not delay on getting that done. If you delay it, then your car will not run right in about 3-6 months from now.