O2 sensor

[maxocoupal]

for the begenning I just want to say sorry about my spelling im french from Quebec.recently i had a check engin light on,i borrow my frend scanner and it said i have a problem with my first o2 sensor.So i change it, even the second one disconnect the battery to reset the computer of the car , and i still have the check engine light on.does anyone know what can be the problem, my car is a mazda protege 1999 1.6L

[Wonderboy]

Welcome to EM!

Air from the outside could be getting into the exhaust system somehwere - check to see if there are any rust holes anywhere near the O2 sensor in your exhaust manifold/pipe. Also check for loose connections between any of these pipes that would let outside air in. I've had this problem on every car I've owned to date probably because of the salty roads in wintertime. I just end up needing to replace the long central exhaust pipe that extends between the catalytic converter and the muffler.

[some_other_dave]

A 1999 model year might have more than one O2 sensor. Did you replace the wrong one?

You should also check the electrical connections to the sensor(s).

-soD

[SKIN]

My car said that the rear O2 sensor was bad. I replaced it. Then it said that the front one was bad. I replaced that. Now it is fine. My point is... some_other_dave is probably correct in his assumption that you have more then one.