Code P0421. What does that mean?!

My daughter's Ford Probe: 1996. About 140K, 2.0 liter, 4 cyl, automatic. All this shouldn't really matter. I think this "check engine" code is standard for
any Ford. The counter person at Advance Auto read it for free but he was mystified by what it meant. P0421 is Catalyst System Efficiency below limit - Bank No.1. Is there anybody who can convert that to English? A look under the hood shows what looks like a catalytic converter with right there at the exhaust manifold with an Oxygen sensor at either end of it. Each sensor has four wires. Does Bank 1 mean the first oxygen sensor? There are other codes for Bank 2. Should I automatically assume the catylitic converter is bad at 140K? I think they want this to be cryptic so a mechanic can charge more money. The car runs tip top and doesn't burn any oil. It just passed inspection but next year "check engine" lights fail inspection in our state. Any advice would be appreciated. Scott Ssaund9084
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This site has what you're looking for.... http://www.obd-codes.com/trouble_codes/generic/p0421.php
Basically, it's either your cat or the O2 sensor behind the cat... read the article above for more info.

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p.s. Also see http://www.alldata.com/TSB/19/96191472.html

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I have had a similar problem with my 1997 Taurus 3.0 Vulcan engine, currently at 118K miles. The "Service Engine Soon Light" has been coming on from the P0421 code intermittently for about a year now. I have had it reset, or it will often reset itself on subsequent test cycles. I am going to try swapping the downstream O2 sensors (the V-6 has two cats, and 2 downstream sensors, thus 2 "banks") to see if the problem presists with the other downstream sensor on bank 1, and/or now shows up on bank 2. Because it is intermittent, I suspect that I am having problems with the signal from the downstream O2 sensor, rather than an actual problem wth converter performance. My research on this code indicates that it is very common on vehicles above 75K miles, and in most cases, does NOT correlate with excessive emissions due to a depleted cat conveter. Most vehicles with this code when tested by a tailpipe "sniffer" will pass the applicable emissions limits. However, with emissions programs now using the OBDII code status only as a pass/fail criteria for cars so equipped, that may not matter. I haven't had to test the system yet, as thankfully, the code was not present (it had cleared itself a few days prior) when I had to submit to a Connecticut emissons test in March. My plan was to ask for a tailpipe test to confirm the code if I had to take the test with the code present. Would be interested to know if anyone has ever challeged the system this way , and what the outcome was.
On your 2 liter, don't think you can do the sensor swap diagnostic like I am going to do , as you only have one "bank". But changing the downstream O2 sensor would be a prudent first step financially before committing to a cat replacement. On my 3.0 V-6, a cat replacement would be very expensive, as a "Y pipe", containing 2 converters for both banks must be changed. Nice design for affordability, Ford! Just like the design of making a $20 ball joint as an intergral part of a $300 hub carrier casting, or a $10 wheel bearing an intergral part of a $150 wheel hub cartridge assembly! I'll stop my ranting now....
Chris Bowne Stonington, CT
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SSaund9084 wrote:

i got a Code P0401 on my 96 contour.. its related to the carbon buidup behind the throttle body being blocked... if you go to www.contour.org web site(a contour web site and mentinon the code 401 you will see what it is all about... they have pictures of a before and after cleanup of the thing and this will give you alot of help... just about all fords of the year 96 get this problem with the code 401...
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SSaund9084 wrote:

sorry i thought you said Code 401.. gotta get my glasses????
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