1996 bmw 318ti...engine code 420???

i have this code 420 from my scanner obd-11. catalyst system efficiency below threshold bank-1
anyone know what that means...maybe my cat is bad??????...hope not$$$$$.

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http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm
This is a list of the OBD II Codes.
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
Your code seems ti indicate that the After CAT O2 Sensor is not working.
Your CAT could be bad, but the sensor costs in the range of $25 and the CAT is closer to $250. You pick the failure you would prefer to fix. HINT: I go with the cheapest thing first. HINT 2: There is not very much that can go wrong with a CAT, assuming you feed your car the correct kind of fuel -- unleaded.

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Well except that maybe after about ten years or so the catalyst becomes poisoned and stops working. Platinum costs a fortune (~$1k/ounce or 25/g) so cat's are very expensive. OTOH the platinum can be recovered so an exchange should be a lot cheaper than ouotright purchase.
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Perhaps, but a new sensor costs even less, and can be replaced at home. I only suggested that it should be replaced before electing to buy a new CAT.

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Jeff Strickland wrote:

I have never seen an O2 sensor that cost $25. More like $100 and $75 if you search hard. But I do agree that the most likely failure is the sensor.
--
-Fred W

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19831993ranger wrote:

With OBDII there are specific codes (3 according to my Peake code reader) for the aftercat O2 sensor - poor response time, failed heater etc. So, it really appears that you have a bad cat - sorry. If it were just a bad aftercat O2 sensor, you are supposed to get one of the specific codes for failure of the sensor itself, instead of this poor catalyst system efficiency code. Seems like this particular code would not be useful, unless there were, in fact, the additional O2 sensor tests to verify proper O2 sensor operation and thereby validate the cat failure code.
Sorry,
Frank
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Raybender wrote:

Not really. I had O2 sensors go bad in both my E34 and E36, both of which also have those more specific codes and in both cases it was just the generic "out of rabnge" errors that I was getting.
I'd still do the sensors first. If it has not been changed and the car has anywhere near 100k miles it is due. If it was recently changed it ios possible the new one had an infantile failure or was contaminated by something.
Beats the heck out of replacing the cat... Those bad-boys are expensive.
--
-Fred W

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I had the same problem with my m44 engine, but it occured at 110,000 miles. I went down to the local checker auto parts (CSK), and asked the clerk about it and he thought it was was more than likely the oxygen sensors. by replacing both O2 sensors the problem went away until a rock hit the front one and broke it off. I would assume that the same problem exists on yours. Usually O2 sensors are really stuck in there so get a toarch and get them red hot they come out really easy then.When putting the new ones in use some of the sensor safe anti-seize, but be sure to only get it on the threads and not the sensor. Also do not touch the sensor part, the oils and salt on you fingers will dramatically shorten the life of the sensor. The comment in this thread about the O2 sensors costing about $75 and $100 is resonable, the best price I found for these was at www.bavauto.com. The biggest problem with the cat is that a lot of places still use the higher sulpher gasoline which is the main thing that clogs cats now. If you are in Minnesota or Wisconsin I would suggest using the holiday blue planet gas, it is complient with the new nation wide fuel standards that will take effect in 2007 for low sulpher, if not wait 6 months.
On Sun, 05 Feb 2006 13:39:32 -0500, 19831993ranger wrote:

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