[TassieBMW]

My 2005 E90 330i which has 313,000km (194,000 miles) has codes for both catalytic converters (29F4 and 29F5).

For a while I could clear these and it would be a month or two before they came back, but now they're coming back every day or second day after clearing.

Firstly, I'm wondering if there's any actual effect on the car other than decreased emissions efficincy? There is no emissions testing where I live so don't need to worry about that. Unsure if they're bad enough to have an effect on performance, but I assume the car would be throwing other codes if this were the case?

I'm also wondering how likely it would be that the post-cat O2 sensors are causing this, and not the cats themselves.

The car is obviously quite old and not worth a lot now so it doesn't make a lot of sense to spend heaps on new cats and the labour to fit them. The most annoying thing is having the check engine light constantly on, so I won't know if there's an actual problem with the car when I'm driving which annoys me.

Any advice from others who've dealt with this would be much appreciated.

[Brian86]

These cars are a little weird in that they always seem to throw catalyst threshold codes on BOTH banks simultaneously. It'll never just do one side or the other, which is annoying because it eliminates the troubleshooting step of swapping sensors to identify sensor vs cat.

(The stupid harness couplers are different front/rear too)

It doesn't effect the car's performance at all. It just throws the code for emissions failure.

Only way to find out is to install two new sensors.

I have fouled cat's due to a nasty oil ingestion episode a few years back.

My car has double-stacked spark plug anti-fouler spacers, with with about a 1/4" hole letting exhaust gasses access the sensor in the down stream ones.

It works pretty good. The DME still knows something is wrong. It always has O2 malfunction codes in the DME but it only very rarely throws a malfunction lamp based on US OBD emissions thresholds. Usually after three consecutive highway speed drive cycles. Your car may vary as non-US emissions failure thresholds may be different.

[Saico]

Hi both, check your short term fuel trims if they even get calculated. Afaik rear lambdas are also used for fuel trimming.

With cat error active they are deactivated on that bank.

Also, I had an error on one bank only and fuel trims were not working there only.

[TassieBMW]

Thanks for the replies.

Interesting to know that fuel trims may be effected as a result.
All my sensors are original and are probably overdue for replacement so perhaps I should just replace them. Not sure how difficult to access they all are?

If I could find cats cheaply I suspect those are a pain to get to and replace?

It would be nice to just code out those two faults so the CEL doesn't always come on, the spark plug spacer idea isn't a bad one though.

[Brian86]

You're overdue for all for O2 sensors at 200k miles.

Cat's are integrated into the manifolds. Not too hard to replace (rust notwithstanding). They can be finessed in and out without moving the engine or anything important.

If you can get cat's... send me a set. In the states scrap cat's are valuable enough that even whole junk cars usually have them stripped off before you get your hands on it... and it's basically illegal to resell salvaged ones.

[jadams161]

That is a ton of miles on the stock converters and o2 sensors. The codes are because the converters have lost their ability to clean the exhaust gasses. They also are probably covered in oil because we all know how much these engines love to eat motor oil. If you change cats and O2 sensors your car will run much better.

[TassieBMW]

I wonder if I go to an exhaust shop and get them to either take out the converters or replace them with some smaller modern sports ones if I might be able to get a bit more sound and performance out of the old girl at the same time?

Might be a good opportunity to turn lemons into lemonade so to speak.
Thoughts on this idea?