Options to fix a P0430 code (Bank 2 Cat efficiency level below threadhold)

[ImolarotII]

My 03 has no tune and is on it's original cats. Is the only way to resolve this to replace the cats? This is also a California car so I'm due for SMOG.

[ATB88]

It could be faulty secondary (post-cat) O2 sensors. That's a cheaper and easier thing to try first, so I'd start there. If they've got around 100k miles or more on them, they're due for a change anyway (and the pre-cat sensors are too). My understanding is that cats don't often fail on these cars if your engine's running properly.

If you're still getting the code after that, then, could be your cats. Luckily, if you just want to keep things stock, good used replacement cats for our cars are pretty easy and cheap to source ($100-$200 tops), since most people remove their stock catted headers to upgrade their exhaust. Kind of a bitch of an install though.

[ImolarotII]

This might be a stupid question but, how reliable are used cats for our cars? Like if I buy this take a look at it and say, "yep, this wont throw a code, looks newer than mine". Is there a way visually check cats that I know would last me 60k miles at least?

[ATB88]

Yeah that's not a dumb question. I might have a dumb answer though.. Ultimately, as far as I can tell, you mostly have to go by the previous owner's word that they were working well when they removed them. If they're really toast/damaged you'll hear them rattle when you shake the headers around, that's a definite red flag, but short of that, I think the only thing you can really do is maybe get a boroscope up the pipe to inspect visually. If they're not crumbling and don't look clogged, then they're probably fine. The bank 2 cat can actually probably be visually inspected from the end of the pipe without a scope, actually? Again, cat failure doesn't seem common on these cars, and it shouldn't be hard to find a cheap used set that has less than 100k miles on them, in which case, it's unlikely that they'd cause you any problems.

Anecdotally: people buy and install used euro cats on these cars all the time, most of the time paying around $600 for sets with totally unknown mileage. Never heard of anyone getting burned with a bad set. In fact I'm about to install a used set with unknown mileage this weekend! The pipes are really dirty and makes them look quite old, but the cats themselves actually look very clean!

Again, though, start with the secondary oxygen sensors. I think those are more likely to be faulty and are much easier to replace.

[ImolarotII]

And by secondary sensor you mean, O2 sensor on bank 2 (4-5-6) right?

[ATB88]

Not quite, I mean the second oxygen sensor (the one that's after the catalytic converter) on the bank. These cars have 4 oxygen sensors: two primary oxygen sensors (one on each bank and are placed before the catalytic converters, which are used to sense AFR info that the ECU uses for fuel/ignition stuff), and two secondary oxygen sensors (one on each bank and are placed after the catalytic converters, which are used only to monitor the efficiency of the catalytic converters, hence are likely to be your problem here).

Again, though, if the sensors have >100k miles on them, you should replace all 4. The primaries won't fix your fault code, but are actually more important in how the car runs, so it makes sense to do them if you're already going to be replacing the secondaries.

edit: ah, sorry, I realize that you asked that because your code was specifically for bank 2. If you're going to replace one, might as well replace them all. if one's failing now, the other ones won't be far behind. But you could start by just replacing the post-cat bank 2 sensor just to confirm that it isn't the cat itself that's failing, before going ahead and replacing the rest of the sensors. On the other hand, if you're just looking to get by with the cheapest and easiest fix right now so your car can pass smog, the secondary sensor on bank 2 is probably the easiest out of all 4 sensors to access and replace, you can easily do it from under the car. Maybe just have to take the reinforcement plate off first.

[Speed Monkey]

OP, your stock converters are getting tired, and they have packed it up. Contact Forum Member KAIV; he can fix your problem 100% by turning down the post cat O2 sensors’ sensitivity in the ECU, which means your stock exhaust manifolds with converters incorporated into them, can stay in-situ; Kevin is very well known here in the M3 community, and is well respected. Hell, Forum Admin Ian bought his E46 wagon with a S54 engine+gearbox swapped in, including suspension underpinnings I believe. If San Diego is too far for you, perhaps speak to someone at EAS in Anaheim or Lang Racing Development in Lake Forest. If that doesn’t work, speak to Sam at Auto Talent in Carson. If all that fails, speak to Fabryce at GMG Motorsport - their race shop is simply incredible.

[ATB88]

OP, your stock converters are getting tired, and they have packed it up.

What makes you feel like it's more likely to be the cats that are the problem vs the O2 sensor? Not trying to insist that I'm correct, but rather I'm interested in hearing more about likelihood/common-ness of cat failures on these cars?

[PSUEng]

Any update on this? I just got the same code today--totally stock. Trying to figure out what to do, if the post-02 sensor should be replaced, or if the cat really is the problem.

[Jersey_M3]

Was there an update here? Mine just cropped up today with p0430 and p0420. Trying to figure out why post o2 sensors are 99.2 percent and stuck there

[Jersey_M3]

Anyone

[Dxj]

Any luck in resolving this? I get this error every once in a while.

[sev]

youre more than likely either going to turn down the sensitivity or replace your cat. I had to replace the cats on my s54 mcoupe years ago. There could be a small chance your post cat o2 sensor has gotten lazy. You can check with a obd2 scanner to see what the o2 sensor voltage is. I'm not sure on the procedure but there is a way to tell if your o2 sensor is the issue.

For me though nothing I tried worked until i replaced the cat. At the time it wasnt possible to tune down the sensitivity. Keep in mind, as of monday the BAR in california will begin checking for modified ecu code. So using KAIV might not work.

As to why your cats died, it is kind of strange. Did you by chance ever have a misfire condition? I killed my cats by driving 20 miles or so on 1 cylinder misfiring, all the raw fuel got dumped into the cat and some time later, maybe a year or so the cat was dead. Maybe something like that happened?

last option might be to just put a spark plug non fouler on the post o2 cat and hope like hell the smog tech doesnt see it. That usually doesnt bring the code back.