Sonata 2000 1166 and 1167 codes

Hyundai defines this poorly. Mostly the definition indicates that it's a fuel trim (mixture) management issue. Most of the time I see one of these codes, an oxygen sensor is stuck full rich or full lean.

If you have just one of these codes and the other oxygen sensor is behaving normally, the issue is most likely the upstream oxygen sensor on the bank in question (P1166 => rear bank, P1167 => front bank).

If you have both codes, you should first check things that could allow extra/restrict air or fuel into both banks. Typically, this would include fuel pressure issues, blocked air intake, leak in or improperly attached air intake bellows, or other sizeable vacuum leaks.

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Thank you very much. Anything I can do myself or I should take it to the mechanic? How involved is replacing the sensors myself?

If you don't have an oxygen sensor socket, you're unlikely to be able to replace the sensors yourself. Also, note that I don't recommend jumping in and replacing the sensors right away, either.

If you don't fully understand what I'm talking about for your diagnosis, then you're probably better off taking your car to a shop with an excellent reputation for driveability diagnosis and repair. Taking your car to a shop/mechanic that has little experience with this type of diagnosis will probably result in just replacing the sensors.

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Thanks again, everything you say makes a lot of sense as usual! I think (hope) that I know a mechanic that can help me with this issue.