You haven't mentioned whether you repaired the oxygen sensor or not. If you have not repaired the faults which are causing the Oxygen Sensor trouble code and Oxygen Sensor Heater trouble code to set, they will not clear until your make the required repairs.
If your Mercury Tracer failed the smog check due to these trouble codes we recommend you have a smog check repair station verify these components are defective and then go ahead with the repair.
After the repairs you/technician can erase the DTCs (digital trouble codes) and then drive for 300-400 miles to set the "emission monitors", also known as "readiness flags".
posted by SmogTips Support