Help with O2 Sensor

[myneon]

I just bought my first car. A '96 Plymouth Neon (SOHC), 100K miles. The check engine light came on shortly after I got home with the car. I read out the code and got a code 21 (O2 voltage not changing). Last weekend I replaced the front sensor and reset the check engine light. After about 60 miles the light came on again, with code 21 again. Can I recycled the O2 sensor removed from the front and use in the rear? I realize I will have to wire it in due to the wires being shorter on the front sensor. I don't have $65 for a rear sensor and I am willing to give this a try if functionally they are the same. Please let me know if there is anything else
I should look at first.

Thank you

[ikeyballz]

yes, i believe the two O2's ARE interchangable.. (They have universal ones, so go figure..) but i think the rewiring will only be temporary.. the old one will prolly fail, if both have not already been failing in the first place.

[myneon]

Thank you for the info. I will give it a try sometime this week. Last night I was reading a post on the net that indicated the rear O2 sensor is only there to indicate if the Catalytic converted was working or not. Is this true? I seem to be getting arouind 26 miles per gallon and would expert worse if my O2 sensors were really bad. Thanks again...

[denisond3]

The rear O2 sensor has some role in determing if the mixture is correct or not. I damaged the rear one while working on the catylitic converter. Besides the check engine light coming on - our highway mileage dropped from 32 to 27 mpg. (driving on the same highways and the same distances.) If your car has over 100,000 on it, I would think that downstream sensor would be nearly moribund. The upstream sensor wouldnt work any better at the rear end of the cat.converter than it did at the upstream end.
It wont hurt anything to run with a senile O2 sensor in that downstream location - but save your money for a replacement. Meanwhile you can expect the check engine light to be on fairly often.
We have emissions testing here in Fairfax County VA - and if the check engine light is on it will fail the emissions test. Without passing the emissions test - we cant get license plates for the car.
Has your car had its timing belt replaced? Its supposed to be done at 100,000 miles. I advise also replacing the water pump at the same time. The belt may not break until higher mileage - but they seem to be break at 120k or 130k. This can depend on the drivers style.