Mazda MAZDA3 owners have reported 2 problems related to o2 sensor (under the electrical system category). The most recently reported issues are listed below. Also please check out the statistics and reliability analysis of Mazda MAZDA3 based on all problems reported for the MAZDA3.
My brake light housing is melted on both sides. The brake light bulb is melted into the brake light sockets on both the left and right brake lights. I noticed while driving in the city and cars were flagging me to tell me my brake lights are out. I pulled into a auto shop to check and both sides were melted. I had my car since 2013 and everything was original stock. My check engine light flashes and when I had it checked they said it may be faulty fuel pump, because that's the only code that shows and I already had everything replaced. My car very frequently stalls out (highways and city streets) even after replacing the fuel pump and O2 sensor. The passenger airbag light flickers frequently, with and without passengers.
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Since we had this car, we've had to repair the engine oxygen sensor at least 2 times. Why this continues to malfunction we don't know, but at some point we shouldn't have to pay for a faulty engine/electrical system part.