fault code p1123

P0422 indicates a problem with catalyst inefficiency. You probably need a new catalytic converter. This code will eventually return.

P1123 indicates a rich condition. Considering this occurred immediately after replacing the oxygen sensor, I'd suspect the oxygen sensor you installed is defective or isn't compatible with the vehicle. I'd recommend using a factory oxygen sensor.

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the oxygen sensor is (factory oxygen sensor) same a old one. and the technician off (scan tool) tell me, the oxygen sensor work good coze he read this in his scan tool.

and this code P1123 was found after 4 day from change (oxygen sensor)

and need to ask some thing I have program for scan can I see the problem code, by cable between my computer and car without interface or if u have scheme for easy interface i hope to send to me for scan my fault code with my self

thank you

like this photo

prisediag7.jpg picture by kemks

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.

1. 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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I started getting P0422's less than a month after I passed a smog check, so I'm assuming the downstream O2 sensor is bad (the upstream one went bad last year). Is that a reasonable assumption?

Nope. You probably need a new converter. You should, of course, verify the oxygen sensors are properly connected (upstream to upstream connector and downstream to downstream connector) and are displaying normal pattern (other than a large amplitude from the rear sensor). But ultimately, at a probability of 95% or better, the converter isn't working so well.

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the mechanic was tell me he test it my scan tool for measure it and he must between (0:1) if it that O2S will be good and this also in the autodata program ((O2 level at idle speed -------- Vol. % O2

0,1-0,5 ) and i was went to hem to assure this rate is my o2 rate and he was tell me your O2 is good.

and I was went to hem to assure this rate is my o2 rate and he was tell me your O2 is good and he have this volume rate.

the mechanic tell me may be (MAF) must replace it but this is so expensive to me, and I afraid when I change it this code return back

• my fuel consumption is so high.

• I was clean this MAF by (CRC).

O2 voltages between 0 and 1 are normal, but they don't necessarily imply the sensor is functioning properly. The ECM has the capability of adapting to skewed readings from a faulty or improper sensor, causing the voltage readings you describe.

I'd also be interested in your short term and long term fuel trim values, both in the current data stream and in the freeze frame data.

It's possible you damaged the MAF by attempting to clean it, but since the same code was present before and after the cleaning, that's not likely. I, too, doubt the MAF will solve your problem, but I don't have the car in front of me to diagnose, either.

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thanks for your attention, but if you can tell me some thing to assure if my O2S work good or not work or MAF work or not work

coze until now I spend more money for resolved this problem

and the new O2S was had same code from the old one , and this O2S was closed in the factory case and I think the factory made quality test before sell it , this make me suspicion of my O2S is defective if you have procedure for calibration it, please tell me how that.

and when I replaced it with the new , try to be punctual and careful to not transact hard

and thanks for your cooperation

"had same code"

What is this code? I'm not sure you understand what I mean by "factory." Factory means a part obtained through the vehicle manufacturer's (Hyundai in this case) distribution network (in the U.S., that would be a Hyundai dealer) and in the vehicle manufacturer's packaging.

For checking the air flow sensor, you'll be interested in technical service bulletin 01-36-022. You can view it at

you'll need to register for an account if you don't have one. It gives specifications for normal air flow readings. This TSB was intended for diagnosing a P1128 code, so instead of MAF readings that are too low, you'll be looking for MAF readings that may be too high.

Unfortunately, there's little good way to test an oxygen sensor in the field. Checking for normal fluctuation between 0 and 1 Volt (a certain number of high and low switches in a certain period of time) is the best a mechanic can typically do. But as I said previously, meeting these criteria doesn't mean the sensor is good. Beyond that, the only other option we'd have without some sort of sensor-testing apparatus would be to replace the sensor with one known to work properly.

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thanks for your replay i will tray to test another O2 one

I was found the flex pipe is broken, are this reason for this fault code?

Could be. Start by fixing the pipe. Too much fresh air in the exhaust can confuse the oxygen sensors.

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first I try to scan the fault code with another mechanic. the first mechanic found P1123 but another one, he found in the (X431 scan tool)

P0422

I was replaced flex pipe and ensure no have any leaking

and don't clear the fault code when I drive by my car after many miles, I found my (check lamp) is close with it self

but when refill fuel (92) I found the check lamp return open