Contour Enthusiasts Group Archives Forums General Troubleshooting OBD Code P0420

My auto technician read the subject code for my "check engine" light as BANK 1 CAT EFFICIENCY BELOW LIMIT. His diagnostic tool listed 8 or 9 possible causes. I recently bought this car (98 Silver Frost SVT) with 110,000 miles on it, and the check engine light came on after about 500 miles of driving. The tech reset it and said to come back if it comes on again and he would spend more time (and $$) troubleshooting. It came on again today, after about another 500 miles. I queried the previous owner who said he replaced "both" (?) oxygen sensors in the last 6 months. Any idea what the REAL PROBLEM might be? The car runs GREAT!!!! (No problems except for the stupid light).

You need MIL eliminators to fix this problem.

gut them suckers out, if you get this code like i was, it is just gonna keep coming back unless of course you get the MIL eliminator, but you might as well get ride of them things if it is throwing a code saying the cat is basicly bad, new ones cost out the ass, gutting them cost less than $20

What everyone is trying to say is it looks like your bank 1 precat is bad (this is the one on the firewall side IIRC). You can either get it replaced or "gut it." Replacing it is expensive due to parts and labor. Gutting it is somewhat difficult due to the need to remove the manifold, plus it is technically illegal and could potentially cause your car to have trouble meeting emissions (but probably not). Plus you'll need to install the "MIL eliminator," which is a component that mimics an O2 sensor in order to "fool" the PCM into thinking eveything's cool.

My advice: If you want to save money and have lots of time, tools, and mechanical ability, try gutting it. Otherwise bring it to a shop and get the cat replaced.

If you think gutting your precats will too much of a PITA, you can get some pre-gutted ones from Buckshot. That way, the only PITA will be removing them and re-installing the new ones.

When I was still under warranty I had both manifolds replaced (0420 & 0430) for free. Now, 3 years later, I've started getting 0420 again- intake & intake manifolds are clean, new plugs & injectors about 7,000 mi ago, EGR valve was new with the manifolds. I bit the bullet and got some MSDS headers. Now to get them installed....

Or, if you want brand new ones cheap and want to be legal and have no problems passing emmissions..PM me.

I'm overwhelmed by the gracious responses from the group! Thanks for all the advice so far. I've reset the code (by removing fuses 4 & 11 for 15 minutes), replaced a kind of dirty air filter, put in a few ounces of fuel injector cleaner, and made an appointment next week at the Ford dealership, where the service advisor tells me that for $69 they will find out which of the various and sundry reasons are the true cause of my code P0420 code - stay tuned... (At about 150 miles into the code reset, the CEL remains unlit.) At the present time, if the dealer convinces me to replace the precat, I'll probably go for it, as I am really pressed for time. A major household move is pending to a location where I don't know the mechanics and their reputations. Perhaps I'll initiate another post searching for recommendations of reputable mechanics in the Denver area!!

If you need to repalce the pre-cat it will cost you a ton. If that turns out to be your problem, install MIL eliminators. they make the computer think the cat is working fine so the check engine light wont come on.