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Discussion Starter #1
This is more of a Vegas Odds question than anything:

P0171 and P0174 codes - Too Lean

I cleaned the MAF and checked the hoses for leaks, pretty much exhausting my "more appropriate for late 60's" car repair expertise.

The Check Engine light was on when I picked the car up from some minor body work (some ditz backed into me at a parking lot damaging the rear quarter panel). The body shop takes no responsibility, and I can't really blame them. I only mention this because the gas tank and gas cap, which are sometimes check engine culprits, are in this area.

Regardless, I took the car to an Express Oil Change which I have had good service from. They claimed they could fix it and that they were a good place to bring it. When I checked out, they had replaced an O2 sensor. Reasonable price ($380 including labor). I was briefly relieved. But when I cranked to leave, the check engine is back on.

So, they spend another hour with the car giving a convincing impression that they were trying to figure it out. They have now determined that the catalytic converter needs to be replaced. This doesn't make as much sense to me as the online discussions of the P0171 and P0174 codes. But what do I know.? Their price for the converter itself was $1450 or so.

So here is the question: I am disinclined to put $2000 into a car that, even though I love it, would only sell for around $6K to $7K. Plus, it would really suck if I did that and the light stayed on. Plus I have a C8 on order (whatever that means)..

1. From you guys that really know something about these cars, how likely is it that replacing the converter is a logical step and that it could fix the check engine light?

2. I found a converter on eBay that is new and claims to fit my car for $224 including shipping "Catalytic Converter Fits 2009 - 2012 Hyundai Genesis 3.8L V6 GAS DOHC" and "Brand New - CATCO". Any reason to consider this suspect? I would be less disillusioned paying $300 to buy and install this and still have a check engine illuminating the cockpit.

So, what are my odds on fixing the check engine by replacing a catalytic converter?
 

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I'd rather do it myself
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No if the converter is bad you will get a P0420 code or similar. Your codes mean the ECU is running the FIs at maximum at times and cannot deliver enough fuel. Hence the lean codes.

Seeing as it is happening on both banks that would probably rule out hardware that is not shared. Maybe a fuel pump/filter issue?

How many miles on the car? Do you have a scanner that can read in real time the O2 voltages?
 

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Discussion Starter #3
No if the converter is bad you will get a P0420 code or similar. Your codes mean the ECU is running the FIs at maximum at times and cannot deliver enough fuel. Hence the lean codes.

Seeing as it is happening on both banks that would probably rule out hardware that is not shared. Maybe a fuel pump/filter issue?

How many miles on the car? Do you have a scanner that can read in real time the O2 voltages?
105,000 miles.

The P0171 and P0174 codes I listed were from a one-off scan I did with a borrowed scanner at AutoZone. Of course, the mechanics did their own scan. I don't know exactly what they saw, but they did not challenge my "Too Lean Both Banks" intro. What he saw led him to replace one of the CO sensors, saying it was not reading at all. After the initial work ultimately failed to extinguish the check engine and after additional time spent, he showed me that all of the sensors were showing dynamic data (I guess voltages). The one he pointed out was like 0.0xxx or 0.1xxx... sadly cant remember... but it was fluctuating. The mechanic had driven the car away for a long while, and when he came back I heard him telling someone else that it would read low a while and then go high for a while, then go back low.

Note: I do not doubt that the check engine was off when they first turned it over to me. When I left the second time, the light was off. But I stopped, turned the engine off, waited a minute, and started again and the light was back.

I'll go back to AutoZone and read it again to see if I get the same codes as I got before.

I wouldn't mind spending a little more if I was confident the "light problem" was resolved. But I am not confident, so I may just drive with the light until I have to think about it again when I trade or sell.

Thanks for the new info!
 

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I believe the first sentence in this post is the key to your answer. You have a vac leak somewhere.

New CAT my ass.................
 

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Discussion Starter #5
No if the converter is bad you will get a P0420 code or similar. Your codes mean the ECU is running the FIs at maximum at times and cannot deliver enough fuel. Hence the lean codes.

Seeing as it is happening on both banks that would probably rule out hardware that is not shared. Maybe a fuel pump/filter issue?

How many miles on the car? Do you have a scanner that can read in real time the O2 voltages?
I believe the first sentence in this post is the key to your answer. You have a vac leak somewhere.

New CAT my ass.................
Thanks. My thoughts as well. I'll borrow AutoZone's scanner and check again. If the P0171 and P0174 codes remain, I'll suck it up and take it to the local Hyundai dealer.
 

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Find the vac leak. Use the old WD40 method. You'll clean your engine bay in the process.
While your at it run a few techron bottles in your tank. In case your injectors are funky.
(Do the cheap easy stuff first). If your wrong you ve done some maintenance
 

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dry ice

put some in a container with some warm water.
wave it close/around the engine as it's running.

you should see where the fog is being sucked in and idle will change/stumble as the fog is basically CO2
 

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You probably have an exhaust leak that’s happening after the cat converters. Check your flex pipes, muffler, exhaust system, etc. demand a refund from corporate for the o2 sensor that was senselessly replaced
 

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Discussion Starter #9
You probably have an exhaust leak that’s happening after the cat converters. Check your flex pipes, muffler, exhaust system, etc. demand a refund from corporate for the o2 sensor that was senselessly replaced
I talked to the mechanics at Express Oil Change. I haven't demanded my money back... yet. I would have to be convinced it really was senseless. They are still standing by their cat converter diagnosis. The thing is, if I knew I could have them install an aftermarket converter ($230 instead of Hyundai's $1450) and the light would go out, I would be "ok" with the $700. But I do not know this. And, from your point of view, it definitely won't.

I got a new ECU snapshot from Auto Zone:

(Includes repeats)

P0037 HO2S Heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P0037 HO2S heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P2271 O2 Sensor Signal Stuck Rich - Bank 1, Sensor 2
P0037 HO2S Heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P2271 O2 Sensor Signal Stuck Rich - Bank 1, Sensor 2

Is there any chance at all that Express Oil Change is correct?

Or, did their replacement of the sensor just screw it up worse? The P0171 and P0174 codes are gone.

The car seems to run as well as it ever did. Ignoring the Check Engine Light remains an option.

We didn't have problems like these back in the 70s
 

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I talked to the mechanics at Express Oil Change. I haven't demanded my money back... yet. I would have to be convinced it really was senseless. They are still standing by their cat converter diagnosis. The thing is, if I knew I could have them install an aftermarket converter ($230 instead of Hyundai's $1450) and the light would go out, I would be "ok" with the $700. But I do not know this. And, from your point of view, it definitely won't.

I got a new ECU snapshot from Auto Zone:

(Includes repeats)

P0037 HO2S Heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P0037 HO2S heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P2271 O2 Sensor Signal Stuck Rich - Bank 1, Sensor 2
P0037 HO2S Heater Control Circuit Low (Bank 1, Sensor 2)
P0140 O2 Circuit No Activity Detected (Bank 1, Sensor 2)
P0138 O2 Circuit High Voltage (Bank 1, Sensor 2)
P2271 O2 Sensor Signal Stuck Rich - Bank 1, Sensor 2

Is there any chance at all that Express Oil Change is correct?

Or, did their replacement of the sensor just screw it up worse? The P0171 and P0174 codes are gone.

The car seems to run as well as it ever did. Ignoring the Check Engine Light remains an option.

We didn't have problems like these back in the 70s
Yea the repeats don’t matter in this case with the oil change place, because you brought it to them to diagnose the problem(s)causing the p0171 and p0174 codes so the stored or repeat codes or whatever are irrelevant. Your issue is that you paid them 380.00 to fix the problem you brought it to them for, which wasn’t fixed, because the cel came right back on after getting it. For that reason alone, demand your 380.00 back. Clear your cel codes and Then, if the codes persist, take it to a COMPETENT and REPUTABLE mechanic that won’t rip you off. Oil change places have a bad rep for screwing up peoples repairs or being outright liars and thieves regarding problems they claim to fix but don’t fix.

I honestly don’t think you have a cat issue. Does your start? Does it shut off while driving? Does it misfire? Do any of the cel’s say cat converter in the description of the trouble codes? I would clear the codes and drive it and see if the light comes back on, THEN diagnose from there.
 

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Besides that lists of codes all correlate to an issue you’ve probably had with one of your oxygen sensors.
 
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