Hello!

This is my first post here! (Texas)
I have a 2009 G37 convertible. I got it in June 22 and I love the car (i changed from a 4th gen prelude). I've had no problems with the car. Ive changed the rotors, pads, valve cover gasket, intake gasket, oil pan, spark coils, spark plugs and clock spring.
The car was driving fine until a month ago. My check engine light came on with the code P0430. I took it to the shop to get the catalytic converters replaced since there were no other codes and i needed to renew registration within 2 days. I didn't have a lot of money for OEM ones, so i bought a pair from ebay. I was expecting to get codes after replacing them with ebay ones. I swapped both cats and got both p0430 and p0420 codes. I then decided to install defoulers but it only cleared the P0420 left the P0430 code. I decided to swap both rear bank sensors with each other to see if it was the sensors. After i did that i reset the ecu, ran it and after 60 miles i got the P0430 code again. I decided to buy a new o2 sensor (DENSO 2344380) and swapped it out with the sensor that was throwing the code. I reset the ecu and codes and after driving it, I got the same P0430.

Here is the weird part!
I decided to swap the new sensor into bank 1 and the bank 1 sensor into bank 2. I figured this would rule out the sensor since it was a new one i was swapping. After driving it about 90 miles the P0430 went away but now I'm getting a P0420 code. What is this? Lol
I need help clearing this code for how to approach it thank you!

Here is a live data video when i had the P0430 code before i changed the 02 sensor. Any insights?


As of right now the only code is the P0420 code.
I did the following already.
-replaced both cats (ebay)
-replaced o2 sensor (DENSO 2344380)
-installed defoulers
-Clean both MAF sensors
-Did Ecu reset procedure
-Disconnected battery
-Gas cap is always tight
-Changed fuel station multiple times.

 

If i follow your logic, it would seem that the new sensor is causing the problem since the code followed that sensor.

FYI, from the FSM,

The ECM monitors the switching frequency ratio of air fuel ratio (A/F) sensor 1 and heated oxygen sensor 2. A three way catalyst 1 with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase. When the frequency ratio of A/F sensor 1 and heated oxygen sensor 2 approaches a specified limit value, the three way catalyst 1 malfunction is diagnosed.

P0420 Catalyst system efficiency below threshold (bank 1)
P0430 Catalyst system efficiency below threshold (bank 2)

• Three way catalyst (manifold) does not operate properly.
• Three way catalyst (manifold) does not have enough oxygen storage capacity

Posssible causes:
• Three way catalyst (manifold)
• Exhaust tube
• Intake air leaks
• Fuel injector
• Fuel injector leaks
• Spark plug • Improper ignition timing

 

I will try to do the exhaust leak test tomorrow?

Is there anyway to trouble shoot the rest with the snap on scanner?
I have the FSM but i was a bit confused by the wording to troubleshoot it. Ill search up videos on how to troubleshoot. I'm more of a visual learner.

Could i troubleshoot the coils by unplugging the coil from the plug while the car is on? I was told if the car shakes/trembles then it is good. If there is no change when i unplug it it, then it is bad.

Thank you. I appreciate your help!

 

I know its a pain, but the first thing i would recomend is switching your new sensor back to Bank 2 again and see if the code swaps back to P0430 before looking into anything else.
You might have a wiring issue on the sensor plugs also, hard to say. The best way to troubleshoot that is to wiggle the wires around and see if anything changes.

Just threw in the FSM info in case you didnt have access to it. most likeley if it were related to the ignition/fuel delivery systems, you would get other codes. And exhaust or intake leaks tend to drive the VQ to the lean side, which would also cause a code.

 

I will swap it back then.
I don't mind the troubleshooting or going through the pain. I enjoy working on cars but not when i its the only one i need and the registration is expired lol.
I believe the car is running lean most of the time. My mpg dropped for sure. There aren't anymore codes.



This picture is from the video i linked. its about 6 minutes of standing in my driveway.

This one is about 15-20 driving at different speeds in the access road. same day and code

 

You mentioned using non foulers and then you replaced your HO2s. The foulers are in the O2 and not the AFs right?

If they are, you might want to mess around with longer foulers if you dont find an exhaust leak. Your O2 readings are all over the place but more importantly they're changing rather quickly instead of a linear increase/decrease over time.
They also sell some foulers with a catalytic core in them that should help.

If it's not a leak I suspect that the new cats have a smaller cell count per size which regardless what you do it will trigger codes. This would be resolved by adding additional lenght between the HO2s and the pipe.

FYI 90% of the exahusts for VQs end up warping over time. Enough that it kill any gasket you try to throw at it. A good practice "while the exhaust is out" to take a file/ flat sand paper to the EVERY flange to see if it's sands flat. More than likely it wont and even if this is not your problem you can benefit in the future from sanding them. Flat metal surfaces will be most likely to leak less than funky ones.

Try those first, continue with the logs because any change in that area can show up in the logs.

 

I got a eBay drivers cat cause mine was rattling and I replaced both sensors at the same time. No codes though. Want to say I didn't get the P0430 code from having the cheap cat for maybe 8 months. After that i would reset the ecu for whatever reason and sometimes the light would come back right away or stay off for a couple days. But in June I tried Motul 8100 X-Clean+ 5w-30 and the light has been off ever since, except for when it came on randomly maybe 2 times. Try that and see if it works for you.

 

You are correct.they are in the 02 sensors on the Cats. I have two fouler per Cat. Cat-Non drill fouler-Drilled fouler-o2 sensor.
what if i put some steel mesh inside the foulers?

I would think if the cell count was smaller it would throw both codes.
If it was the gasket then the code wouldn't have changed when i moved the new sensor.
Just brainstorming out loud.

 

I just did the oil change about a week ago but ill try that next time if its still there.