CEL with code P0430 - looks like I need new O2 sensors?

[supark]

So my car got a CEL light today and I got the codes read - looks like I have a P0430 code: Catalyst System Efficiency Below Threshold (bank 2).

My 97 540i-6 has 91k miles on it - so I'm thinking that it's most likely the O2 sensors.

My question is - could the O2 sensors going out have contributed to my rough idle situation that I've been experiencing? Also - can I just replace the O2 sensor on the affected bank? Do I need to replace both the pre and post cat - or just one set?

Thanks in advance!

[Steve530]

The message is telling you that the catalytic convertor is bad. It could be the O2 sensors.

I'd try replacing the after cat O2 sensor on bank 2. Then move on to the before cat sensor. After that, I'd take it to someone with proper diagnostic tools, becuase the convertors are expensive.

[Staggerede34]

definately a bad o2 sensor will leave your car running rough, so when replaced it will run better
im not sure about having to replace all the sensors or just the faulty ones

[thejlevie]

At 91k your pre-cat O2 sensors are probably pretty bad which can cause a rough idle and poor mileage from running rich. The pre-cat O2 sensors are a critical part on the engine management system because they are in the feedback loop for mixture control. The post-cat sensors are only used to tell if the catalytic converters are operating properly and given the more benign conditions at their location they'll last a lot longer than the pre-cat sensors (maybe as much as 200k).

As the O2 sensors age they tend to indicate a higher oxygen level than exists (a lean condition). Based on that the ECU increases fuel flow to try to bet back to a normal mixture. Since the signal from the O2 sensors was bogus the ECU winds up running the engine rich.

The three main causes of catalytic converter failure are mechanical damage, contamination (usually oil or antifreeze), or an engine running rich. For the last of those (rich mixture) the excessive hydrocarbons in the exhaust cause excessive temperatures in the converter, leading to partial melting and blocking of the converter. That may have happened here.

I'd first replace both of the pre-cat O2 sensors (they are due for replacement anyway at that mileage). Then I'd swap the two post cat sensors and see if the problem moves to the other bank. If the problem moves it is just a bad sensor. I suspect that it won't, which would indicate a bad catalytic converter. Sorry...

[supark]

cool - just ordered a new pre-cat O2 sensor - hopefully that'll solve my problem -thansk for the advice!

[thejlevie]

cool - just ordered a new pre-cat O2 sensor - hopefully that'll solve my problem -thansk for the advice!

I hope you ordered two sensors. At that mileage they both need to be replaced.

[supark]

I hope you ordered two sensors. At that mileage they both need to be replaced.

I just got one pre-cat sensor - I'll probably do the other bank soon, but it's not giving me any problems at the moment so I feel safe leaving it alone for now. Partly it's to see if it actually works to get rid of the trouble code - it'd also be awesome if it solves my rough idle problem - two for the price of one. My gas mileage isn't horrendous either (for a 540i) - about 20mpg on average.

[323I Junkie]

My God! Look , I love all of you guys, but....


ON CEL's, you need real diagnosis, look, if it were an O2 sensor, you would have an O2 sensor. While it is possible for an O2 to fail readin "wrong"..its very rare. I am a drivability tech, and most of the time, cat codes are either true cat codes or combustion efficeiency (tuning) issues

To understand this, you have to realize that the older O2's in this scenario look at oxygen....

You then need to realize what a cat does, two basic things but its not limited to:
Stripping oxygen from CO
Oxidizing free C and HC to form CO2 and H20

You climb in there yanking 150 to 200 dollar Bosch or any other quality brand O2's w/o diag andd you are playing a damn expensive lottery game. Listen, why not get a 30 dollar emission test and post your reults up here? I can run them through a lambda calculator and a combustion efficeincy formula and see if what is actually going on with your engine. You need to rememr a cat basically controlls about 3% of emission cleanup, the rest is SUPPOSED to go to engine management. 90% of all O2's are estimated to be replaced while still perfectly functional. 50% of Cats are the same way.


In order to condemn and O2, you have to have a scope diagnosis of it, there really is no other truly accurate way. Even a graphing multimeter will do very little in some cases.I seriously doubt your post-cat O2 sensor is bad. The interval on them seems to be about 150K miles, or NEVER..rememebr, they dont come in contact with as much raw soot, NOX emiission, or such things that strip the thin film of metals of a regualr O2 sensor that casuses it to become lazy or downright dead.


I recommend an emission test at a service garage, post the results, and well go fromthere.

DONT JUST START SWAPPING PARTS. YOU COULD EASILY SPEND MORE THAN A DEALER REPAIR IN THIS PARTICULAR CASE!

[Gid]

I purchased my last O2 sensers from Advanced Auto Parts for $60.00. These were Bosch plug & play.

Gid

[323I Junkie]

You purchased 4 wire or five wire sensors that were "Bosch" for $60 for a 540? :

my jobber price onh a real bosch dedicated sensor is around $115

[323I Junkie]

well, I just looked those up and they are very cheap..my price is 45

[supark]

oh crap - you're right - Autozone has em for $60 each - thanks for the lead.

[thejlevie]

I just got one pre-cat sensor - I'll probably do the other bank soon, but it's not giving me any problems at the moment so I feel safe leaving it alone for now. Partly it's to see if it actually works to get rid of the trouble code - it'd also be awesome if it solves my rough idle problem - two for the price of one. My gas mileage isn't horrendous either (for a 540i) - about 20mpg on average.

The pre-cat sensor isn't going to fix this problem (Catalyst System Efficiency Below Threshold (bank 2)). It is possible (but not likely) that the post-cat O2 sensor on that bank is lying and swapping the post-cat sensors will tell. It is almost certain that the catalytic converter for Bank 2 is bad and you are probably facing replacement of both converters.

The question remains as to why the converter has failed and the pre-cat O2 sensors do have relevance to that (see my earlier post). The bad thing about aged O2 sensors is that they don't produce obvious symptoms or faults, at least not until they get really bad. By then the cat's may have already be damaged by excessive hydrocarbons in the exhaust. And there may be other things going on with the engine that need attention and have relevance to this. A rough idle or misfire dumps raw fuel into the exhaust, which is really bad for the catalytic converters. There are a number of possible causes for that and having the car professionally checked is likely to be cheaper in the long run as compared to throwing parts at the problem and hoping for the best.

[thejlevie]

In order to condemn and O2, you have to have a scope diagnosis of it, there really is no other truly accurate way. Even a graphing multimeter will do very little in some cases.I seriously doubt your post-cat O2 sensor is bad. The interval on them seems to be about 150K miles, or NEVER..rememebr, they dont come in contact with as much raw soot, NOX emiission, or such things that strip the thin film of metals of a regualr O2 sensor that casuses it to become lazy or downright dead.

I completely agree with that. The post-cat O2 sensors very rarely fail.

The pre-cat O2 sensors are a whole different matter and you can see signal degradation as early as 60-70k (as shown on a scope). My experience has been that by 80-90k the output signals are noticably off as compared to a new sensor, hence the suggestion to replace them in this case.

[supark]

I'm just really really hoping that it's not the case that my cats are dead... though in the end I guess it's not a huge deal being that I've already passed emissions as of last month - and changing out the O2 sensors will hopefully get rid of my rough idle.

The idle was noticeably rougher and would miss more often after I did the track day - I was running it pretty hard that day. Would one day of hard running kill a cat?

[thejlevie]

I'd think the car would have to be pretty sick to kill a cat in one track weekend, but that might be enough to finish off a cat that's already been damaged.

If the car is in good condition it usually runs better after a track day rather than worse. That says to me that there may well be other things wrong with the car. If you aren't using the stock airbox and filter I'd be suspicious of a contaminated MAF. Have the plugs been replaced? Have you checked for oil in plug wells (a sign of a leaking valve cover gasket)? What about intake leaks... Or fuel filter? Has the OBD been checked for fault codes?

We'd all rather a problem be a cheap part rather than an expensive one. In the general case fixing problems when they first show up winds up being cheaper than trying to live with a problem and having it cause even more damage. It sounds like the misfires and rough idle have been a problem for while and that probably has contributed to the failure of the catalytic converter.

[supark]

I checked all the usual things - valve cover leaks leading to fouled plugs from oil, ran a scan on a code reader, etc. The fuel filter was just replaced about 2 months ago and the it had a compression test and such done at that time as well. The car had been running rough previously (before I bought it) and at first the mechanic thought it was an intake manifold leak - but it turned out to be a vacuum leak.

I actually drove it from Utah to Seattle and didn't use premium gas on a couple refills - so I'm thought that the injectors might be plugged up from crappy gas - so I put a bottle of chevron techron injector cleaner in there along with 20 gallons of gas. Come to think of it... I got the fault code a few days after I put the techron in there - I'd thought that it wasn't related - but now I'm starting to wonder. At the same time - I can't think of anything the Techron could have done to set off this kind of trouble code...

The rough idle and misfires have actually been a recent occurrence - in the last couple weeks, which is why I'm leaning towards an electrical fault of some kind...

[323I Junkie]

TEchron is great stuff, shouldn't have hurt anything

Like I said, and emissions test (non certified) is the way to go, any 5 gas test will work. Get a printout and post it. You can do that here for 30 bucks

Please, we can help.
The 5 gases measured will tell a LOT about why and if your cat went bad

[supark]

just replaced the bank 2 (driver side) pre-cat O2 sensor yesterday (with the pricier OEM direct replacement), cleared the codes out and took it out for an hour long drive this morning.

Typically it'd take about 20 minutes of continuous driving to get the CEL to come on - and it hasn't shown up again yet.

It might be my imagination but the idle seems a fair bit smoother now. There's still a bit of a light lope every once in a while - but I've felt that in other early 540i's.

I changed out the air filter for good measure and should be getting one of the universal Bosch O2 sensors from Autozone soon for the other bank. Unfortunately, I found out that you can get the universal ones for $60 at autozone after I'd already bought the OEM straight plug-in one from Bimmerzone for $90 along with the new air filter. Oh well - I guess I can run a comparison now between the OEM one and the universal one and see if they both last as long

Keeping my fingers crossed that this will solve my problems - I'll post again in a week or so and update whether it kept the P0430 code from popping up again.

[323I Junkie]

Replace both..at that price, it doesnt pay not too. Im going to go pull one.
Is it a stnadard 4 wire sensor?

Oh, and run run the piss out of it up hill on a freeway in 3rd..then coast 5 miles down the other side....heats up the new sensors then cleans all the carbon out and kind of sets-in the metallic layers..little tech trick

[323I Junkie]

Oh yeah...did you guys know..."O2" sesnors are going up to $1500 dollars

they are supposed to be lifetime products, they are wideband A/F sensors similar to whats on a dyno

[supark]

Yeah - I'm replacing both pre-cat O2 sensors - cheap insurance.

[egreaves20]

Any insight on why my HC limit is high?

HC - Limit 107, my car 106 (barely passed!)
CO% - Limit .57, my car .16
NOx - Limit 1250, my car 832

[killcrap]

post your o2 results. if it is above high(above 2%) compairing it to your HC levels, your car has a slight miss fire. your CO% is relatively low, CO is your rich indicator, if CO is low, like yours your not getting enough combustion to create CO. So check your ignition circuit.

[supark]

Update - this ended up being caused by an intake leak around my IAC valve. One of the hose clamps was getting a little loose on that vaguely "Y" shaped rubber hose, so all it required was a couple dollars worth of new screw type hoses and after a couple minutes of idling the CEL turned off. Woohoo!

I was originally worried that it was an intake manifold leak - so I was squirting carb cleaner around the intake area and blipping the throttle while listening for noises of the cleaner getting sucked up.