When it comes down to it, there are many things that can cause P1123, but
there's a reason I think the problem is with the replacement oxygen
sensor. Here's my logic:
1. P0422 will not set unless the ECM thinks the oxygen sensors are
working correctly. This is because the ECM uses data from the oxygen
sensors to determine catalyst efficiency. Hence, it's reasonably to
assume the oxygen sensor was working properly prior to replacement.
2. P1123 did not set until after the oxygen sensor was replaced. Since
nothing had been done between the original P0422 and the subsequent P1123,
it's reasonable to assume there's some problem with the new oxygen sensor.
If it is indeed a factory part (purchased at Hyundai dealer), then it's
possible it's defective (not likely) or was damaged on installation.
Other things that can cause P1123:
-- stuck open purge control valve
-- excessive fuel pressure
-- air intake restriction
-- defective air flow sensor.
I don't currently have access to the photobucket site, so I cannot see the
picture, but I don't have experience with any of the generic scan tools for
home use. About the only thing I can do is refer you to your owner's
manual for the product.
Also, if you can tell me what the mechanic saw that led him to believe the
new oxygen sensor was functioning properly, that may assist me.
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