How do you replace an oxygen censor - 2006 Ford Expedition XLT

P0420 means that the catalytic converter is operating below efficiency threshold. Normally, you only get this code if both O2 sensors ARE OPERATING PROPERLY. If you change the O2 sensors and still get the same code, it's an indication your catalytic converter needs to be replaced. But before you replace it, ensure that everything else in the engine is operating properly, so that whatever may have damaged your current catalytic converter doesn't damage a new one.

behinde the exuest the first sensor after the engine *(sensor 1)

Sounds like you might need a valve job.

this is the oxygen censors location, hope help....

O2 and oxygen sensor are the same thing and depending on make model and motor there can be anywhere between 1 and 4 O2 sensors on your car they are located in the exhaust pipe or exhaust manifold before catalytic converter also might be one behind converter
sorry i cant be more specif without knowing what motor and model you have

G'day mate well lets start with the O2 (oxygen )censor , it is in the exhaust and does clog up give a spiked reading ( on a graph or multimeter ) instead of a smooth transition like a wave flowing,this will tell all the other censors that the fuel flow/mixture/quality is bad , the rest try to compensate by raising the mixture changing timming etc, get the O2 censor done 1st then go from there, it should calm down once this is done,

The location for these types of sensors varies from vehicle to vehicle.

Odds are your manual won't tell you.

Get a Haynes or Chilton manual (free at most libraries) for your make , model and year.

The location, plus changeout info will be in it.

You would use an oxygen censor socket to repair that. You can buy one for pretty cheap or you can rent one from the parts house. You'll want to disconnect the electrical connection to the O2 censor, slip the socket over it (using the appropriate ratchet) and take it off. You can also use a 7/8 inch wrench on most cars if you can get it in there.

The thermostat will not harm the sensor, but the entire engine control system is designed to operate at 210 degrees, therefore all sensors will not recieve proper information,,,end result may be improper mixture in the exhaust pipe, triggering o2 sensor fault reading!

please replaced the sencor