2004 Chevy Blazer O2 Sensor

There are two 02 sensors actually on the engine. bank one is cylinders 1 3 5 bank 2 is 2 4 6. it controls the fuel to air ratio, if the O2 sensor is not working, the engine goes into limp mode, which means it is just putting as much fuel as possible into the cylinder, which will effect your gas mileage.

The O2 sensor may be fine, the pigtails off the 02 sensor go bad, the connection. I had in my car, i change the 02 sensor twice, then I found someone said the pigtails may be bad, so I cut the cars wiring harness pigtail, and the one coming off the 02 sensor, and directly wired it with the original truck 02 sensor, and it worked. all 02 sensors look similar, they screw in the side of the engine, and just have 4 wires coming off of it.

Try your origional one, and just bypassing the original wire connector, what I did was cut it off, skinned the wires, put some heat shrink rap on it, combined the wires together soldered them together, and heated the wire shrink rap, so that way it is water proof. car works perfect now.

O2 sensor is one of the most misunderstood components. It does nothing except to react to conditions in the exhaust mixture, which are the result of what the remainder of the engine is doing. (proper fuel mix, spark control & blowby gasses in the exhaust stream) Though in reacting, it does give the ecm info to which the ecm reacts, generally it is not the sensor itself which is bad, but another malfunction or condition that is providing the sensor with something "bad to read"! Anything from improper base timing, a vacuum leak, a bad exhaust gasket or worn timing chain can change exhaust composition enough to affect what the sensor is seeing! If changing sensor, it is located on exhaust pipe, ahead lof cat (looks like a part of a spark plug with one or two wires coming out of the top. Do not install without using anti-seize compound or you will never get it out again!!
good luck