P0421 Code After EGR Valve Cleaning 2003 P5

[pkpk]

Hey guys, don't blast me - I spent a long time (well over an hour) searching and reading the forums, and found plenty of info about P0421 code, and EGR Valve issues, but nothing that made them seem like they could possibly related. Here's the background, but first let me say that everything on my 2003 Protege5 is stock.

My engine randomly started missing, and I was getting a P0300 random misfire code, as well as a code showing that I was running lean. After researching on this forum, I concluded that it was most likely the coils, so I replaced them. I had only had this issue for a couple weeks before replacing the coils. It seemed to fix my P0300, but my idle was a little rough, and I was feeling manly, so I went for the EGR valve cleaning to see if it would help, and it was way more of a PITA than I expected, but I got it done.

For 115K miles on the car, the EGR valve wasn't actually that bad, but it was totally awesome when I was finished cleaning it. I reinstalled it, and it drove all right around town, so I took it on a 150 mile trip, and just as I was arriving home, my CEL came on. The code is P0421, and I am hoping so hard someone will say it's not my cat. I reused my aluminum gasket for the EGR, because it looked to be in good condition. My question, I guess, is can this problem be caused by a faulty EGR valve gasket? Or could I have knocked something loose when I was messing with the EGR valve? Just seems like a major coincidence that as soon as I do the EGR valve job, I get this new code. Everyone's insight is greatly appreciated. This forum has been a big help.

 

[Tzar177]

If you were misfiring, then raw fuel was probably dumped into your pre-cat and ruined it. Most likely you will need to replace your cat

 

[pkpk]

If you were misfiring, then raw fuel was probably dumped into your pre-cat and ruined it. Most likely you will need to replace your cat

Is there a reason it wouldn't have thrown the code earlier?

 

[Tzar177]

Is there a reason it wouldn't have thrown the code earlier?

Getting the P0421 code is a sign your cat is going bad. You prolly wouldn't have thrown a code til it was bad enuf. It is prolly unrelated to the egr

 

[P-Funk!]

^werd.

 

[02Protege'5]

damn it all, i didn't want to hear this either, i have the same issue....
I recently did some tune up jobs, new plugs, new alternator and ac belt. Changed tranny fluid. Cleaned my EGR valve. After all that I got the p0300 code. i did some research and figured my coils were going bad, so i changed those out. the car is still running badly and the check engine light came back on, i haven't had an opportunity to have it put on the reader yet.

reading around on the forums, I think I can gut my pre-cat and do a non-fouler trick on the second 02 sensor to solve my problem? would i also need to gut my second cat as well?

 

[Tzar177]

damn it all, i didn't want to hear this either, i have the same issue....
I recently did some tune up jobs, new plugs, new alternator and ac belt. Changed tranny fluid. Cleaned my EGR valve. After all that I got the p0300 code. i did some research and figured my coils were going bad, so i changed those out. the car is still running badly and the check engine light came back on, i haven't had an opportunity to have it put on the reader yet.

reading around on the forums, I think I can gut my pre-cat and do a non-fouler trick on the second 02 sensor to solve my problem? would i also need to gut my second cat as well?

No just the first one

 

[JReichle1]

Is there a reason it wouldn't have thrown the code earlier?

The second o2 sensor monitors catalyist efficiency (how well the cat is doing it's job) the code is not set untill the exhaust gAsses are 1.5 times the federal standard. The egr being installed improperly (not torqued correctly, bad gasket) can cause an exhaust leak that might cause a code for a bad cat. Take it to a good mechanic and have them do a computer scan and check the live data from the vehicle as well as a quick visual inspection. Good luck!

 

[02Protege'5]

ok, just went back to the shop and we had an OBDII scanner, woot. Anyway i have code po421 "warm up cat effiency low bank 1". My diagnosis: The raw fuel ****** up my pre-cat and now my first o2 sensor is getting wacked readings.

Solution: Remove my pre-cat and gut it, re-install. remove my second 02 sensor and re-install with the non fouler trick.

Sound like im on the right track?

thanks,

-Tony

 

[Tzar177]

ok, just went back to the shop and we had an OBDII scanner, woot. Anyway i have code po421 "warm up cat effiency low bank 1". My diagnosis: The raw fuel ****** up my pre-cat and now my first o2 sensor is getting wacked readings.

Solution: Remove my pre-cat and gut it, re-install. remove my second 02 sensor and re-install with the non fouler trick.

Sound like im on the right track?

thanks,

-Tony

You got it

 

[JReichle1]

I did the non fouler on my 2nd o2 with mu obx header install. Been on almost a year and still no check engine light. You could do a header. Haha. My obx makes me speed...

 

[02Protege'5]

am i going to need new exhaust header gaskets, a new gasket between the header and cat and cat to the j-pipe? also, just brainstorming here. when i cleaned my EGR valve, there was no gasket. I don't know if i may have overlooked this the first time i removed the EGR valve and have now been running without one....

 

[Tzar177]

am i going to need new exhaust header gaskets, a new gasket between the header and cat and cat to the j-pipe? also, just brainstorming here. when i cleaned my EGR valve, there was no gasket. I don't know if i may have overlooked this the first time i removed the EGR valve and have now been running without one....

The egr gasket is metal and basically blends in unless you know its there. Sometimes it will even stick to the intake manifold. Might want to take it back off to check for the gasket. You might not need a new exhaust manifold gasket but you may need a new one between the cat after gutting it

 

[dandan2]

this code poppes up about once a month for me! i dont have a cat i need to do the nonfouler trick.

 

[tommyd]

I have the EXACT same problem right now. Was throwing a 0300, cleaned the EGR, still got it. Replaced plugs and wires. Still had it. Replaced EGR (what the hell), still there. Finally replaced coils and *bingo* no more code. All this over the course of two weeks with the car driving like it was on its last legs.

Car is great now, but has started throwing a 0421. I'm guessing I'm in the same boat as users 02Protege'5 and pkpk. Argh.

 

[mexicansoljah81]

Currently getting headers installed, gonna do non fouler trick tonight and see what happens.

I too had the p0300 and got coils, timing belt, spark plugs, wires, egr valve cleaned, and water pump replaced. Now no more code, but Now have the p0421, so instead of replacing cat, I ordered obx headers, getting rid of that stupid cat. Should b good to go. I will post pics when all is done.

 

[Dragnfly Racing]

Anyone wanna explain the non-fouler trick to a newbie?

 

[02Protege'5]

http://www.mazdas247.com/forum/show...ving-cat-with-Non-Fouler&highlight=non+fouler

Basically you take two spark plug de-foulers. Use a 1/2" drill bit to completely drill one out. screw the one you drill out into the second unmodified de-fouler, screw that whole thing into where your second O2 sensor goes, and then the o2 sensor into that whole rig. the second sensor gets just enough of the exhaust to trick it into thinking there is a pre-cat installed. has worked for me for 50k miles with no CEL