P0420 & P0430 at same time

[Thats550]

I had system to lean bank 1. I had misfire cylinder 6 and 8. With Catalyst System Efficiency less than Threshold bank 1 and 2. Which is why I thought maybe it was intake runners. Well pulled off manifold and intake runners are not broken. It was dirty so I cleaned the manifold out. Reinstalled and cleared DTCs and only thing coming back now is p0420 and p0430. Idk if I should replace the cats or replace 02 sensors. I tried some cattaclean but the p0420 and p0430 codes came back on. I tried to read the data for the 02 sensors but idk what I'm looking at they were fluctuating good from what I can tell. Any advice or help or suggestions are greatly appriated

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[HKusp]

Are you boosted?

 

[HKusp]

I would start with changing out the rear O2's with Ford units and see if that clears it up. You can try and clean them, but the pricing on them is such that just buying new one's isn't bad.

 

[Thats550]

Are you boosted?

I am not boosted. In at 43k miles and I believe they are original 02s

 

[Thats550]

I am not boosted. In at 43k miles and I believe they are original 02s

But it's is possible that both took a crap at the same time

 

[junits15]

o2 sensor data cannot be use to reliably determine cat health at idle because the cat test doesn't run at idle.

• When you are cruising the system will at some point toggle the mixture slightly rich and slightly lean over and over something like 10-15 times in a row.
• On a good cat, the downstream sensors should remain at a constant voltage during this test if the cat is good as it will absorb the rich pulses and release during the lean pulses. You wont see anything after the cat if the cat is good. Just a flat line.
• On a failed cat, when the mixture is toggled rich the downstream will read rich and when the mixture is toggled lean the downstream will read lean. The cat will act like a passthrough.
• Partially failed cats will initially display a constant voltage on the downstream sensors but after a few toggles the catalyst will becomes saturated and stop working and you'll see the rich/lean toggle on the downstream sensors again.

This is what sets the P0420/P0430 codes, so if you are having those codes this is what's happening. Downstream sensors are also used for biasing the upstream sensors as well as emissions monitoring. A failing sensor may exhibit itself as unexplainable fuel trims.


It is extremely unlikely that both failed at exactly the same time, but not impossible. Can you post a log of the 02 sensor voltage during a drive and at idle?

 

[Dave2013M3]

I had this happen on my E92 M3. I replaced the rear 02 sensor only for it to rear its ugly head again. It was the upstream 02 sensor. I replaced that one and I didn't get those codes. Turned out when I had my test pipes put on the tech twisted the 02 sensors to get them off of the OEM Xpipe.

 

[Thats550]

It is extremely unlikely that both failed at exactly the same time, but not impossible. Can you post a log of the 02 sensor voltage during a drive and at idle?

Yes I can after work today. U want me to send graphs for the 02s after the cats? I can do it at idle and while drive normal or driving hard? Thanks so much. I can do that in about 3-4 hours I get off so I'll post back then.

 

[Thats550]

I had this happen on my E92 M3. I replaced the rear 02 sensor only for it to rear its ugly head again. It was the upstream 02 sensor. I replaced that one and I didn't get those codes. Turned out when I had my test pipes put on the tech twisted the 02 sensors to get them off of the OEM Xpipe.

Interesting. So maybe I should replace them all. But I have access to live data logs I should be able to test them if they are good or bad right

 

[junits15]

Yes I can after work today. U want me to send graphs for the 02s after the cats? I can do it at idle and while drive normal or driving hard? Thanks so much. I can do that in about 3-4 hours I get off so I'll post back then.

Try to get the following parameters on one log
Bank 1 upstream o2 (before cats)
Bank 1 downstream o2 (after cats)
Bank 2 upstream o2 (before cats)
Bank 2 downstream o2 (after cats)

First clear the codes.

Then do one idling for like a minute, then one driving at steady speed on the highway for a while after the car is warmed up all the way. Go for like a 15 minute highway drive, no hard pulls needed

 

[Thats550]

Okay so im having trouble uploading the video. I took a video at idle of the 02 sensor graphs. Is the sensor 1 in amperage and sensor 2 in voltage? I think that's what I'm seeing. Any website I can use for uploading the video like imgur but for videos. Otherwise I can clip it smaller I tried cutting it in half to 30 seconds but that didn't work rither

 

[Thats550]

This is basically what it was doing for the idle for a minute

 

[ZZMike]

Did the rear O2 sensors switch like the upstream ones while driving as well?

If that screenshot was taken at idle after a drive, things don't look good for the cats.

But a screenshot of all 4 at a steady speed with moderate load would help diagnose.

 

[Thats550]

But a screenshot of all 4 at a steady speed with moderate load would help diagnose.

Here's a pic from the video when driving. I was going about 40 mph I'd say. engine was nice and hot. When it spikes up is when I let off the gas. Also no they stayed as (v)

 

[ZZMike]

Thanks, yeah, the back HO2S mirroring the front when at operating temp amd under light load shows that the cats are bad.

Since they are mirror images of each other, no catalytic action is taking place. The rears should normally be steady, and slightly high.

Any gas additives used or anything? Really kind of rare to have them both go South at the same time.

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