99' Elantra Check Engine Light "code P1128

On the way home from work my check engine light came on so I stopped at Auto Zone and the manager put the code reader on my car and it said "p1128 Manufactures controlled air metering" this was all it said so
the manager took the code inside to his computer and entered it and it said "upstream heated 02 sensors swapped" Does anyone know what these could mean or what has gone bad?
Thanks
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You only have one upstream oxygen sensor on the Elantra, so "upstream heated 02 sensors swapped" is not a valid diagnosis.
This code indicates the computer has been supplying more fuel than it thinks it should have to based on the other sensors' readings. This is a (somewhat) common problem with 2000-2001 Accents It's okay to reference the tsb on this issue (01-36-022), but don't use it for diagnosis because the values will be different than those on an Elantra. If you want a better understanding of what the code means, tsb 98-36-001 provides a reasonable amount of information.
What you want to look for is unmetered air entering the engine (meaning it leaks into the intake without having to go through the air flow sensor). The primary ways this happens are leaking pcv hoses, intake hoses not fully attached to the air flow sensor, and intake hoses torn. If there are no issues with unmetered air, then you probably need a new air flow sensor.
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Thank you for the help, on the way home today the check engine light went out, should I still try to find the cause of the code or wait and see if it comes back on?
On Mon, 01 May 2006 18:46:27 -0400, "hyundaitech"

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Any time an OBD-II powertrain code begins with P1xxx it is a manufacturer-specific code. The database that autozone was pulling from is probably not hyundai-specific. P1128 could mean something completely different on say, a GM product, Ford, Chrysler, etc. P0xxx codes are generally standard across manufacturers.
Might want to check HMA service(www.hmaservice.com) and look at what the hyundai definitions for your code are.
Chris
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Thanks for the info, I went to the site and registered but I could not find the codes anywhere.
On 2 May 2006 10:21:20 -0700, snipped-for-privacy@gmail.com wrote:

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The diagnostic information for engine codes is in the "fuel" section of the shop manual.
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