how to change upstream 02 sensor

 

Step 1 Unplug it
Step 2 Unbolt it
Step 3 Reverse process
Step 4 Clear stored codes

 

What is the O2 sensor? Where is it located?

 

The front is easy. Normally it's te rear that is bad in a 4cylinder. And it's connector is under the passenger seat

 

thats not correct. go underneath the car and its the o2 sensor before the cat. its attached to the header and the connector is on top of the tranny.

its the downstream that is after the cat and connects under the passenger seat.