OBD Code P0420 - CEG Archives

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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.

Originally posted by HITMANinMI:
You need MIL eliminators to fix this problem.

That wouldn't be a fix unless he has a removed/gutted cats/precats.
Most likely precats are going bad. You can gut them and then get the MIL eliminator (i think you need it for gutted precats). It could also be a bad cat. If you have under 80k miles then it's possible that Ford has to fix it for free. Could be some other problem as well, not sure what, you never really know what code can be resulting from.

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.

Originally posted by HITMANinMI:
You need MIL eliminators to fix this problem.

With respect, you really need to stop posting replies like this unless you really know what you are talking about.

There are many triggers for the p0420 code. At 110k, the intake system on this car is likely to be badly gunked up. Unless we know what the service history on this car is and what condition it is in now, I's hold off on telling him anything like 'you need mil eliminators'.

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.

Originally posted by HITMANinMI:
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.

I think if you're giving advices like that you should also inform him that doing this is against federal law...

On the other hand, running with plugged exhausts/cats will damage the car on the long run and no MIL eliminator will save you from that.

Tiv

check with a reputable ford dealer. last I heard they were having a recall for the cats going bad. beyond the 80k emissions warranty.

this my be a dumm question but what is mil eliminators?

Originally posted by Blancas2020:
this my be a dumm question but what is mil eliminators?

Not dumb at all. I guess I should spelled it out for those who dont know. MIL = Malfunction Indicator Light, which is basically the check engine light. Anyways MIL eliminators you place after I think, it may be before, the downstream O2 sensor if your cat goes bad. This makes the computer think the cat is working correctly so you dont get a check engine light. So MIL eliminators eliminate the check engine light.

OK, been to the dealership and...source of the code was unable to be discovered. Per the service advisor, if the cats were bad, I should be seeing driveability problems (I am not). Oxy sensors were monitored and checked out OK. Since they were unable to successfully diagnose the problem, they discounted the $69 "check engine light diagnosis" to $59. Stay tuned.

Originally posted by Tom501:
OK, been to the dealership and...source of the code was unable to be discovered. Per the service advisor, if the cats were bad, I should be seeing driveability problems (I am not). Oxy sensors were monitored and checked out OK. Since they were unable to successfully diagnose the problem, they discounted the $69 "check engine light diagnosis" to $59. Stay tuned.

No you dont notice any driveability probelms if your cats are bad I believe.

Originally posted by HITMANinMI:
No you dont notice any driveability probelms if your cats are bad I believe.

Correct AFAIK... a cat can be operating below spec and still not cause driveability issues. But if you let it go and pretend the problem doesn't exist, it eventually will.

I took my car to autozone when the CEL came on and I got the same code you have. I called my mechanic and he told me to ignore it because many times it is a fluke. That was 3 weeks ago, the light is still on but the car is running OK. Until this morning...but my new problem is seemingly unrelated. I am going to do some intake cleaning this weekend and see if that does the trick...if not I may try the gutting suggestions since I live in the boonedocks where no-ones car could meet emissions!

My CSVT is throwing a P0420 code as well and say "catalyst efficiency below threshold." My car only has 45k and the service tech at the Ford dealership told me that it is probably a bad precat and is covered by the 8/80,000 emission warranty. My car runs fine, except I think the fuel pump is also going out because it bucks at 5,000 rpms when I only have 1/4 tank or less.

I'm pretty sure this link has been pasted before, but it does a great job of explaining things.

http://www.fordscorpio.co.uk/catmonitor.htm

This is an excellent article and should be required reading for all CEGers!

Originally posted by MarkO:
There are many triggers for the p0420 code. At 110k, the intake system on this car is likely to be badly gunked up. Unless we know what the service history on this car is and what condition it is in now, I's hold off on telling him anything like 'you need mil eliminators'.

Can vacuum leaks cause a P0420 code?

Maybe check the long term fuel trim.

Where can I buy an mil eliminator?

http://www.mileliminators.com/ $29 per pair