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Possible Solution to P0420 Code

G

greasemonkey1489

Hard-core CEG'er
Joined
Apr 14, 2008
Messages
1,568
Location
Bloomington/Normal, IL
The code means that the Cat efficiency is low, so that means that the preset value for the downstream O2 is out of the range that the ECU has programmed, thus a fault. Possible reasons for the cat efficiency being low would be a rich-running engine, or just rich exhaust.

One big problem with these cars (v6 Duratec) is the EGR passages clogging in the intake manifold right behind where the throttle body mounts. Also the failure of the EGR valve itself due to carbon and a poor design. The EGR valve is vacuum operated so the EGR solenoid may not be able to tell that the valve is not completely opening.

Back to the EGR passages.. if the passages are clogged, then the engine cannot cycle exhaust gases back through the engine to "dilute" the fuel/air charge causing a slightly "rich" condition. EGR systems are to reduce emissions and increase fuel economy, especially at cruising speeds (>45mph). SO, if the fumes are too rich, the downstream o2's sample the fumes and the voltage reading indicates a "low efficiency" after the catalyst, you get a lovely, orange CEL.

So, pull of those throttle bodies, test the EGR valves, scrape out that carbon and let's see what happens...!

I have had the 420 code cleared 3 times and it has been back after both downstream o2's were replaced.. Cleaining my intake stuff this weekend and I will clear codes and update.
 
greasemonkey1489 said:
The code means that the Cat efficiency is low, so that mean that the preset value for the downstream O2 is out of the range that the ECU has programmed, thus a fault. Possible reasons for the cat efficiency being low would be a rich-running engine, or just rich exhaust.

One big problem with these cars (v6 Duratec) is the EGR passages clogging in the intake manifold right behind where the throttle body mounts. Also the failure of the EGR valve itself due to carbon and a poor design. The EGR valve is vacuum operated so the EGR solenoid may not be able to tell that the valve is not completely opening.

Back to the EGR passages.. if the passages are clogged, then the engine cannot cycle exhaust gases back through the engine to "dilute" the fuel/air charge causing a slightly "rich" condition. EGR systems are to reduce emissions and increase fuel economy, especially at cruising speeds (>45mph). SO, if the fumes are too rich, the downstream o2's sample the fumes and the voltage reading indicates a "low efficiency" after the catalyst, you get a lovely, orange CEL.

So, pull of those throttle bodies, test the EGR valves, scrape out that carbon and let's see what happens...!

I have had the 420 code cleared 3 times and it has been back after both downstream o2's were replaced.. Cleaining my intake stuff this weekend and I will clear codes and update.
Click to expand...

i think you got it down! i cleaned my egr and my TB a few months ago.....CAKED with carbon. reinstalled them and wow! you guessed it!
i'm dying to clean my upper and lower intakes. i did on my previous svt, and the damn thing ran sooo much better, also a good idea.
 
I had the 0420 code, mine decided to be a bit extreme though, my Car would just refuse to start about mid day

Took it up to my friends shop, UIM and LIM gaskets were leaking.... Now back with a new code specifically point to EGR. Going to try the cleaning myself to see if I can clear it.

Just to be clear, take off the TB and should be able to see the ports on the UIM? Just clean out with carb cleaner?
 
The EGR ports are like "veins" almost. Hopefully someone has a picture.


They are at the bottom of the opening of the UIM where the throttle body attaches. You'll have to use a small screwdriver to actually scrape and dig out the carbon. Then spray with carb cleaner to rinse out the crud
 
only issue with what you posted is that the egr valve doesn't often fail on these cars. yes the passages do get clogged up.

also the PCM flash to open up the range that trips the P0420 does work. I know that the intake on my parents 99 has not been cleaned. If had a P0420 awhile ago and the pcm flash took car of it. the P0420 was back recently but the secondaries where only half working. don't believe its been back since.

but either way the intake and egr passages should be cleaned.
 
No, I read a TSB about frequent problems with failure of the EGR valve. And I'm not saying to NOT get your ECU reflashed.. If this does not work for me, that's the next step.

I could only see the secondaries causing that code if the engine isn't getting enough air
 
greasemonkey1489 said:
No, I read a TSB about frequent problems with failure of the EGR valve. And I'm not saying to NOT get your ECU reflashed.. If this does not work for me, that's the next step.

I could only see the secondaries causing that code if the engine isn't getting enough air
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only thing is from experience on the site the egr valve rarely fails. its the dpfe sensor that does, and that causes the egr to not function correctly, which could lead to what you discribed.
 
Sunroof gears, MTX-75 differentials, gas filler necks, Duratec water pumps... those are common failures. I could probably count the number of EGR failures I've seen here on one hand. Now, I have heard of the DPFE failing, and there was an updated part released by Ford, so if the EGR stops working it could very likely be from that sensor.
 
Well... back to my original post. Im pinpointing the EGR system as a whole as being a cause for the P0420 code. I will post pictures of my intake cleaning this weekend and you guys (lesser experienced) can see what I mean by blocked EGR passages.
 
BrApple said:
its been well documented before. not sure if the pictures still exist or not but new ones can't hurt anything.
Click to expand...

Well im glad people like you exist to tell newer members that they are wasting their time. I looked for pics, archives are obviously not working. The only reason I started this thread is because when someone asks for a solution to this, one of the number 1 responses (from the know-it-all moderators) is to get your ECU reflashed. Ok, great. That helps with part of the issue.. well the car still runs funny and fuel economy is mediocre but hey, no CEL right?
 
greasemonkey1489 said:
Well im glad people like you exist to tell newer members that they are wasting their time. I looked for pics, archives are obviously not working. The only reason I started this thread is because when someone asks for a solution to this, one of the number 1 responses (from the know-it-all moderators) is to get your ECU reflashed. Ok, great. That helps with part of the issue.. well the car still runs funny and fuel economy is mediocre but hey, no CEL right?
Click to expand...


you need to stop taking everything so personally ....

I didn't say you where wasting your time. I'm just saying that its been covered before. I figured the the old posted pictures where not there anymore, so new pictures would be good. have you checked the FTP site that someone has set up? instruction on how to access it are in one of the stickies, in the duratec forum, iirc. maybe there is a picture there.

the PCM reflash is what Ford perscribed for the P0420 and P0430 check engine lights since the pre-cats often don't go bad. FYI, with the PCM reflash fuel mileage improved and the gas smell went away on my parents 99.

I would say if you have poor fuel mileage still there is another issue. The only thing the PCm flash does is make the cel shut off for the P0420 and P0430 codes.

btw, I don't know it all ... but when you have been active and helping people for 8 years you get an idea of what the general problem are and how they are fixed, along with how to troubleshoot this platform.
 
Partial fail on my part... Cleaned the EGR passage today and noticed a HUGE difference, but I only had my phone cam.

There was soo much carbon build up that when I took the gasket off it was caked on in the form of the opening. New gasket and some cleaning took care of all that. Popped off the egr valve to see how bad it was over there but not much there. The gasket was completely shot though. No taking it off, straight scraping it off. New gasket and good as new. No more CEL and running like new!

Thanks to all of you 'know-it-alls' On here :)
 
99svtc said:
Partial fail on my part... Cleaned the EGR passage today and noticed a HUGE difference, but I only had my phone cam.

There was soo much carbon build up that when I took the gasket off it was caked on in the form of the opening. New gasket and some cleaning took care of all that. Popped off the egr valve to see how bad it was over there but not much there. The gasket was completely shot though. No taking it off, straight scraping it off. New gasket and good as new. No more CEL and running like new!

Thanks to all of you 'know-it-alls' On here :)
Click to expand...

Now that's what I like to hear.
 
99svtc said:
Partial fail on my part... Cleaned the EGR passage today and noticed a HUGE difference, but I only had my phone cam.

There was soo much carbon build up that when I took the gasket off it was caked on in the form of the opening. New gasket and some cleaning took care of all that. Popped off the egr valve to see how bad it was over there but not much there. The gasket was completely shot though. No taking it off, straight scraping it off. New gasket and good as new. No more CEL and running like new!

Thanks to all of you 'know-it-alls' On here :)
Click to expand...


so I take it your cleared the codes when you did this work, or did it go out on its own? if you reset the pcm there is a still a chance the code will come back, sometimes it just takes some time. most of the time when people are getting the pre-cat codes they can come and go for awhile before they stay on all the time. report back in like a month and then we can go from there.

but then again egr passage cleaning is more maintinence then anything.
 
BrApple said:
so I take it your cleared the codes when you did this work, or did it go out on its own? if you reset the pcm there is a still a chance the code will come back, sometimes it just takes some time. most of the time when people are getting the pre-cat codes they can come and go for awhile before they stay on all the time. report back in like a month and then we can go from there.

but then again egr passage cleaning is more maintinence then anything.
Click to expand...


One clarification, the 0420 code has been cleared for over a month with replacing the UIM and LIM gaskets. My most recent code was I think 0401 for the EGR valve itself. Every time I had cleared the code it came back within minutes. After the cleaning I total drove for about an hour. Maybe I'm just being optimistic in saying issue resolved, either way MUCH bettrer drive. I did get my throttle hang back though...:crazy:
 
99svtc said:
One clarification, the 0420 code has been cleared for over a month with replacing the UIM and LIM gaskets. My most recent code was I think 0401 for the EGR valve itself. Every time I had cleared the code it came back within minutes. After the cleaning I total drove for about an hour. Maybe I'm just being optimistic in saying issue resolved, either way MUCH bettrer drive. I did get my throttle hang back though...:crazy:
Click to expand...

P0401 is not for the egr valve itself. P0401 typically means that the egr passages behind the tb are plugged up and need to be cleaned. P0402 points to the dpfe sensor.

search P0401, its been covered.
 
I run a zip tie through the passage ways that go from the throttle body opening on the UIM to the EGR. This will get out just about everything that was clogged up and costs you nothing to try.
 
blu_fuz said:
I run a zip tie through the passage ways that go from the throttle body opening on the UIM to the EGR. This will get out just about everything that was clogged up and costs you nothing to try.
Click to expand...

I took some of my daughters Pipe cleaners and twisted them together to make it nice and sturdy. Another nice alternative to the zip tie
 
BrApple said:
P0401 is not for the egr valve itself. P0401 typically means that the egr passages behind the tb are plugged up and need to be cleaned. P0402 points to the dpfe sensor.

search P0401, its been covered.
Click to expand...

Your right, I had my codes crossed...
 
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