The oxygen sensor was replaced but the 'check engine' light won't go out. Now what? Which octane fuel is best? AAA's Car Doctor has answers.

Should that be the case for your vehicle failing an emission test, it is worth inspecting the O2 sensor for malfunctioning, the injectors for leaks, or a worn-out fuel pump.

Rounding out the five most common problems found to trigger the check engine light after ignition coil and spark plug, and O2 sensor were 3) catalytic converter, 4) loose or damaged fuel cap and 5 ...

The oxygen sensor was replaced but the 'check engine' light won't go out. Now what? Which octane fuel is best? AAA's Car Doctor has answers.