P2098 code, cleared, then P0430 code - ChatGPT told me catalytic converter

Preface, I tried using chatgpt to diagnose my car and it "seemed" surprisingly efficient and accurate. I got a P2098 ( Post Catalyst Fuel Trim System for Bank 2 is too lean) , and cleared it a few months back. No issues since until today. It came back on again today, so I cleared it again. Then later today I got a P0430 (Catalyst System Efficiency is Below Threshold for Bank 2). Just that, I didn't get the P2098 Chat GPT said my catalytic converter is likely toast. It then asked for oil usage and mileage. 1-2 qts every 5000 miles at 165,000 It again confirmed the catalytic converter. I'm 44 so I'm not a full ai geek, but this seems a pretty thorough diagnosis... Is ChatGPT right?

Or u can get a scanner and view the o2 outputs so u can properly diagnose the issue. It could also be a bad o2 sensor or the wiring too the sensor at that milage.

ChatGPT is ALWAYS right.....NOT. If you do have a low efficiency, it can be the cats, but as De Jeeper states, you want to look at the outputs and new O2 sensors are cheap, check out rockauto Bosch units. Not the same codes, but check this out: https://rennlist.com/forums/996-foru...o2-sensor.html

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Oh this is helpful, thanks! Can the Torque app measure these properly? I have the paid version, and was checking the up & downstream values but couldn't figure out how to chart them... I have lots of mechanical experience but diagnosing o2 values etc. is not my strong point. I was honestly just a bit surprised how thorough chat GPT was in this case. Given that searching for 02 sensor code diagnosis on the internet often leads to dozens of forum threads to read... Chat GPT broke it down super easy. It probably saved me an hour or two of research to point me in the right direction.

I believe Torque can at least read them, use my graphs to see what kind of range they are in. Here is a great resource for 996 fault codes, this is for the 996.1, I imagine the 996.2 for O2 sensors would be exactly the same, but you can just go up the tree to get to your model year. https://charm.li/Porsche/1999/911%20...8%20DTC%20%29/ Start by studying those. ChatGPT gets you going in the correct direction, but I have found its diagnostics can be wrong at least half the time. It acts like it knows for sure your issue.

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Thanks for this. I'll hopefully dig into it more this weekend. Yeah, I was just surprised how quickly the answer was synthesized and easy to understand the process. In no way will I spend the money on new cats without proper diagnostics.

Jumping back on this. I'm prepping for a wedding party in a few weeks so this has been on the backburner. Quick question... My car has not started a few times, mostly when it's in the cold. The battery is at 12.2v normally, ~10v when starting and then ~14.3 when running so I think the alternator is good. Could these P0430 code cause hard starting?

Doubtful. If it did, you would already have noticed a severe drivability issue.

No. P0430 code is unrelated to Battery/Starting/Charging system. Here are the signals you need to measure to see if the cat is bad. The post o2 sensor should not follow the pre o2 sensor. If you see this type of signal when you increase revs, the cat is bad. After changing the cat, you will see the signal in the bottom picture. The post o2 signal stays high. As for your starting issue, it could be many things: battery, Y-cable, starter. I don't know how much voltage drops when the starter is running but this is good data. Maybe someone else knows. My Cayenne had a hot start problem where the voltage would dip to 7V when starting. The starter windings, when hot, were expanding and making the motor bind. In your case if it's happening only after sitting a few days, it could be any of the 3 things, or something else. Sorry, lot's of words and little help.

Great info on the cat, there is not enough information regrading the starting issue. Does it turn over? The voltages that were posted show a healthy battery so I assume it is turning over but not starting. But can't understand it from the OP's info.

OP - As others mention the 430 is a bad cat, bad O2 sensor pre- or post- (depending on which signal is out of tolerance). The voltage issue can be addressed by checking the y cable leads for corrosion and security. You can improve grounding by adding an additional cable. This can be done with a 24� single black battery cable run from the starter to the SAI bracket bolt.

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Yes, it turns over and starts like normal. It has never had a "honda" type start, I don't know if this is normal. As in, a honda starts exactly the same every time. Mine changes periodically, but in general has always started a little slow. For the last 40k miles or so. However if I park it outside (Minnesota winter) for a few hours, it usually won't start. I've had one time where it was inside in a 45 degree garage and it still died. I'm going to check for a parasitic drain. This is something I've never heard of, the grounding. I'll look for some threads on this. I only have the Torque app to check O2 sensors. Does anyone have a good description of which sensors to mointor and how to chart them on the torque app?

Dont know the torque app but @golock911 litterally posted the sensor and graph info 3 posts up?

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Thanks, I saw and read the post. I was asking specifically about the torque app because there a handful of sensors you can monitor, and they are all named different than the graph. There is no "upstream o2". It's a bit convoluted. So I figured I'd ask the specific question. I was able to find the sensors. And I found a graphing function on the torque app,but it looks nothing like that graph. So it wasn't all too helpful. I messaged with a mechanic friend a bit, sent him some videos and am going to try replacing my upstream O2 sensors.

Many times they r labled pre (before) cat and post (after) cat. The nomenclature gets confusing sometimes. U also have to lool at the units and make sure its measuring the correct thing. For the o2 it should have a range of 0.0-1 volt.

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This is unrelated to the O2 sensor, but the battery voltage...~14.3V when running. Is that when the engine is up to temp and fans are running? If not, you may have a Y cable issue.

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That was just a cold start. What is the y cable issue?

The Y cable, also known as the starter/alternator cable is a failure point in the design of the electrical system. Picture this. A large gauge wire runs from the alternator to the starter. At the starter connection, a similar large gauge wire is mechanically bonded to the first wire and from there it goes to the battery. In order for the alternator to charge the battery, the current has to run through this aforementioned mechanical bond of the two wires. The bond is not sealed from the elements and over time and depending on the environment, corrosion sets in and impedes the flow of current to the battery. As the corrosion worsens over time, the battery becomes starved of current and slowly ceases to get fully charged. You can see this on the car's voltmeter. If at cold start, you have 14.3V but it drops to 13V or 12V after the engine is warm, you likely have a corroded Y cable. To most people, it looks like the battery is failing. Maybe the engine won't start or cranks slowly. If you don't know about this failure point, you might be wasting money buying a battery or a new alternator. In my first year of ownership, I was having this issue and I took it to a really world class Porsche mechanic (who I won't name) who rolled out his Snap-On electrical system tester and told me I needed a new alternator and new battery. He did not know about the 996 Y cable and he did not know I am an electrical engineer. I took his advice and wasted $600+ to replace a year-old battery and the original alternator only to find out neither one had failed. It was the Y cable. And two years later, out went the rebuilt Bosch alternator so I had to buy another. This time I avoided the rebuilt option. The new Bosch is a big improvement over the rebuilt. This is my voltmeter with the engine warm and all the fans are on. It drops a little from cold. If you look at it head on, it is 14V. That is as low as it gets.

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Oh this is super helpful! Since mine was at 14+ when started, I figured it's not the alternator, so I replaced the battery. So far it's starting good but I'll definitely check if the voltage drops to check for the Y cable. Your explanation was awesome! I also decided to order 2 upstream O2 sensors to try out on this P0430 code. I couldn't figure out how to make a good data chart in the torque app. But I've been able to find the O2 up and down stream sensors and watch them live. I'll update if it fixes my code....

Update - I installed new upstream 02 sensors. Pretty easy Job. But now I have P0131 & 0151(O2 sensor low voltage on bank 1&2) Quick search indicates possible exhaust leak or o2 sensor issues. I installed Bosche 16433's. Remove the old without issues, install the new without issues. Didn't drop or knock them. Cleaned the connectors before connecting them. They felt plenty tight unless somehow they loosened after installation? What did I Miss?

Unknown. This could be showing some wires chewed on by rodents that were fine until you start moving them around. Could be many things. I'm reading that P0131 is for bank1 and P0151 is bank2. Can you double check? Look closely at the wiring from the connection back to where they go into invisibility. Do you see broken or chewed insulation? I would recommend putting the old ones back in to check if this is now a permanent condition. If yes, find the bad wires. If no, go back to your scanner and take a picture of the sensor voltages and post them. I think you said you cold see it on the scanner, yes?

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You are correct. I think I mis spoke in my earlier post. It's showing low voltage on both new sensors. Everything was clean and clear upon replacement. No visible chewed or damaged wires. The new sensors went in stress free on the wires. I connected my Torque app and both sensors show zero voltage. Could my plugs be in backwards? Does the female plug allow you to install it backwards? That's the only thing i can think of. I'd have a hard time imagining that 2 new o2 sensors are bad.

Okay, so the plugs can't be done incorrectly. I also disconnected the battery for an hour. I found on another thread that this can reset the computer & help, but nothing. I set my Torque app to go to 2 decimal points reading the sensors so I can at least see if maybe the voltage is just really faint, but not expecting much. Earlier it was posted that the ground on these can be an issue? Is there a write up somewhere to improve the o2 sensor ground? I'm kinda lost as to what's going on.

You need to post graphs of the O2 sensors in service. This is really not that hard, if you feel you are over your head, I would consider bring it to a shop with a bi directional scanner to log them and I'm sure it could be troubleshot in just a few minutes. Best of luck!

Change one of your O2 sensors back to the old ones, erase the codes, and see if both codes return after driving for a bit. This is to eliminate the possibility of installing bad parts.

So I finally made it back to my house with the old o2 sensor & tools. Swapped one back in and sure enough, it reads voltage on my torque app. I cleared the codes & I'll verify if only the bank 2 throws a code this time. I ordered 2 new ones. I can't fully understand how I would get 2 faulty o2 sensors but I understand bad batches happen... The old and new part numbers are exactly the same. Build is exactly the same. Wires all look perfect, not pinched or anything. Hopefully I just get a P0151 to confirm my suspicion. I'll get replacement o2 sensors to install later this week. The car

Since you�re able to read the voltage via Torque, it�s no longer necessary for you to drive your car. It�s very probable that your new O2 sensors have issues. I�m not sure whether it�s because it�s a bad batch or if they�re counterfeit. Where did you buy the new sensors from?

Update: I originally got a P2098 ( Post Catalyst Fuel Trim System for Bank 2 is too lean) , and cleared it a few months back. No issues since until recently. It came back on again recently, so I cleared it again. Then later I got a P0430 (Catalyst System Efficiency is Below Threshold for Bank 2). Just that, I didn't get the P2098 ChatGPT told me I had a bad catalytic converter, and was quite confident in it... I researched a bit and ordered new upstream O2 sensors (bank 1 and 2) from Rock auto. Installation was pretty straight forward, but I got new codes for low voltage at both O2 sensors. I swapped one old one back in and sure enough I got voltage again. So I ordered another set of the same O2 sensors from Rock Auto. After installation, I have voltage to both! I think I just got unlucky enough to get 2 bad ones. Probably a bad batch. So far, I have about 200 miles on the car and no engine codes! I was having a bit of difficulty tracking this on the Torque app. But I was able to find O2 Bank 1 sensor 1 (and 2) and the same for bank 2. I set these up in the torque app as a medium digital gauge with background graph, and changed the display to show 2 decimal points. I'm saying all of this because it was kinda a pain to figure this all out. Hoping it can help others in the future.

I hope you purchased the Bosch sensors. And if you are having a low efficiency you will definitely need to change the post cat O2 sensors if it comes back. It's a comparison of before and after sensors to validate efficiency. And if ChatGPT is very confident, don't believe it. It always acts that way until you tell it that it was wrong and it says "Oh yea, you were right".

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Yup, Bosche sensors. Same PN. So far, no codes have popped. I'm hoping it stays that way. At first I was a bit blown away by the ChatGPT diagnosis. It seemed so thorough and it totally made sense. But before I replaced the cats, i wanted to do all my leg work... These O2 sensor / air fuel ratio codes are a tough one to diagnose. The idea of Chatgpt making sense of complex situations was appealing. But ultimately, wrong. (hopefully)

Did ChatGPT talk at all about a 'lazy' sensor? I had this on a early 2000's Passat. It threw codes that looked like the cat was bad. The response time of the sensor was too slow and would goof up the computer. Caused by old or contaminated sensors. If you replaced the sensors and the problem is gone, this may have been the problem. If the live data on your scanner is fast enough, you can see it.

@danmurphymn Have the sensors solved your issue? I previously had a P2098 which I cleared, then recently a P0430 along with misfire on 1,2,5, & 6. My thoughts are that I do have bad cats as I ran this with bore scoring for a while which could foul the cats.

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No, not yet. I've only put in the downstream O2 sensor. I have the upstream as I'm continuing to get a code (P0430 I believe). No coded misfires, but the car stumbles on startup if I give it gas and also if I rev it from low end torque. I have my 175k oil change coming up in a week or two, I'll put the upstream O2 in then. I'm not expecting that to fix the issue. I think it's a cat also...

Downstream will have no effect on operation. I would be surprised to see that you had concurrent upstream failures so yes, like you suspect it is probably the cats if you were blowing a lot of oil.

Come to think of it - my exhaust recently developed an internal rattle - bet it is my cat.

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In a previous post about an post O2 sensor problem, the pre O2 sensors were old and could not keep up the signals from the post sensor. This is my only contribution below: Take one of the spares and replace pre O2 sensor on the bank to test for this problem. Having replaced both post sensors, the chance both are bad after replaced is less than 5%. Your problem isn't the post sensor. From my query: (i got a p2098 error on my 996, then a p0430 3 months later. what is the correlation between the errors and a fix to resolve the issues from coming back) The correlation between your P2098 and P0430 errors on Bank 2 is almost certainly an unresolved physical exhaust leak or a failing downstream oxygen (O2) sensor on the driver's side (Bank 2) of your Porsche 996. [ 1 , 2 , 3 ] Because both codes occurred on the exact same engine bank, they represent two progressive stages of the exact same underlying issue. 🔍 Understanding the Correlation To see how these two codes connect over a 3-month timeline, it helps to understand what each code is telling the car's computer (DME): P2098 (Post-Catalyst Fuel Trim Too Lean - Bank 2): This means the downstream O2 sensor detected an abnormally high level of oxygen in the exhaust gas after it passed through the catalytic converter. P0430 (Catalyst Efficiency Below Threshold - Bank 2): This means the DME has noticed that the downstream O2 sensor's readings are fluctuating and mirroring the upstream O2 sensor, concluding that the catalytic converter is no longer storing oxygen or cleaning the exhaust properly. [ 5 , 6 ] The Timeline Connection The Initial Problem (P2098): Three months ago, a tiny exhaust leak likely developed near the Bank 2 catalytic converter flange, or the downstream O2 sensor began to fail and drift. The exhaust pulses pulled outside air into the pipe, tricking the sensor into reading "too much oxygen" (lean). The Progression (P0430): Over the next 3 months, either the exhaust leak grew wider, or the O2 sensor degraded further. Because the downstream sensor was constantly bombarded with unmetered air or failing entirely, its voltage signal became chaotic. The DME interpreted this erratic signal as a dead or useless catalytic converter, triggering the P0430 code. [ 6 , 8 , 9 ] 🛠️ How to Fix the Issue Permanently Before buying an expensive new catalytic converter, follow these diagnostic steps from most likely to least likely: 1. Inspect for Exhaust Leaks (The Most Common 996 Culprit) The exhaust manifolds, collector flanges, and gaskets on the Porsche M96 engine are notorious for rusting, cracking, and warping. Action: Safely jack up the car and inspect the driver's side (Bank 2) exhaust section. Look closely for black soot marks around the manifold gaskets, the metal flanges connecting to the catalytic converter, and the O2 sensor bungs. Pro-Tip: A professional smoke test of the exhaust system is the most definitive way to find a hairline crack that only opens up when the metal gets hot. Fix any leaks by replacing the gaskets or sealing cracks. [ 2 , 3 , 11 , 12 ] 2. Swap or Replace the Post-Catalyst O2 Sensors If the exhaust is completely sealed, the downstream sensor itself is likely lazy or failing. Action: You can test this by swapping the Bank 1 and Bank 2 downstream O2 sensors (they are identical). Clear the codes and drive the car. If the code switches to Bank 1 (P2096 or P0420), you know the sensor is bad. Fix: Replace the sensor. Always use OEM Bosch sensors on the 996. Cheap aftermarket sensors frequently cause false lean and catalyst codes to return on European cars. [ 1 , 2 , 10 ] 3. Porsche DME Software Flash Porsche issued a technical service bulletin regarding an error in the early diagnostic software of the 996 DME. The software can mistakenly log P2098 aging faults even when the O2 sensors are completely operational. Fix: If you clear all leaks and sensors check out fine, a Porsche specialist or dealer using a PIWIS tester may need to flash your DME to the latest factory software version. [ 13 , 14 ] 4. Replace the Catalytic Converter If you have verified there are zero exhaust leaks, the O2 sensors are brand new, and the code persists, the catalytic converter brick inside the Bank 2 housing has officially degraded or melted. You will need to replace the Bank 2 catalytic converter assembly. [ 2 , 15 , 16 ] To help narrow this down, did you notice any change in exhaust sound (like a ticking noise), or are there any other engine codes present like a misfire (P0300)? Let me know the year of your 996 and if the exhaust is stock or aftermarket. [ 3 , 11 ] AI responses may include mistakes. [1] https://www.go-parts.com/garage/obd-p0430-porsche-911-1998-2005-m96-3-4l [2] https://www.go-parts.com/garage/obd-p2098 [3] https://www.go-parts.com/garage/obd-p0430-porsche-boxster-1997-2004-m96-2-5l [4] https://www.carparts.com/blog/p2098-code-post-catalyst-fuel-trim-system-too-lean-bank-2/ [5] https://obdeleven.com/p0430 [6] https://www.youtube.com/watch?v=ZN_uUKR6wog [7] https://www.fs1inc.com/blog/dtc-p2098-post-catalyst-fuel-trim-system-too-lean-bank-2/ [8] https://www.youtube.com/watch?v=89tdCulNeWQ [9] https://www.facebook.com/MotorAgeMag...0080182156903/ [10] https://www.go-parts.com/garage/obd-p0430-porsche-911-1998-2005-m96-3-4l [11] https://www.go-parts.com/garage/obd-p2096-porsche-911-1999-2004-m96-3-6l [12] https://icarsoft.com/knowledge/article/p2098-troubles [13] https://www.import-car.com/tech-tip-porsche-check-engine-warning-light-activated-with-dtcs-p2096-p2098-set/ [14] https://www.brakeandfrontend.com/tech-tip-porsche-check-engine-warning-light-activated-with-dtcs-p2096-p2098-set/ [15] https://www.justanswer.com/porsche/ikbik-just-po-420-po430-cel-porsche-996-911-c2.html [16] https://www.wranglerforum.com/threads/p0430.2415661/ Hope this helps