Yeah !!! --- P0431 Code

[T2T]

OK, I realize this might be a bit sick of me to be excited about this code - but, I am. I finally have more information to go on to pin-point the issue on my '02 Millenia and the near-constant check engine light for the last 2.5 years.

A little history:

1) The check engine light started to appear about 2.5 years ago. Generic P0400 code was appearing.

2) I cleaned the EGR valve - but the P0400 code appeared within 50 miles.

3) I brought my car to a shop that performed the BG process of cleansing the EGR system. Cost was $250.00. The P0400 code returned within a month.

4) Every 2 years, my Mazda requires an emissions inspection. I'd just clear the code prior to the inspection and the car would pass with flying colors.

5) About 6 months ago, I read more into this issue and how the 2 "snake eyes" can get carboned up within the throttle body. I bought a gasket, removed the throttle body and fully cleaned up the ports. P0400 returned again.

6) About 3 weeks ago, I bought a used EGR valve. Installed it. P0400 returned within 50 miles or so.

7) This past Saturday, I removed the throttle body again as well as the EGR valve at the same time. I purged the "snake eyes" with some flexible copper wire. I then inserted the straw of the carb cleaner can into each of the snake eyes and sprayed like mad ... until carb spray was exiting my EGR ports at the back of the engine. I left the system open for a few hours so most of the fluid could evaporate and dry out. I then reassembled the throttle body and the EGR valve - with a slight hiccup that required me to use a HeliCoil to fix my stripped EGR threads on the block. I also installed a new "used" MAP sensor that I got on the cheap.

8) Sunday, I finished putting everything back together. Took a little test drive and within 10 miles, I'm now getting a P0431 error code.

I'll now be able to purchase the (2) 18MM anti-fouler devices from Napa and perform a little surgery for my O2 sensor. I did read where some people have inserted a small amount (small finger tip size) portion of steel wool to act as a filter between the two anti-fouler devices as you bolt them together.

This "fix" or project for me will have to wait about 2 weeks as I'll be on vacation next week. Though, I'm just happy to finally have a more-focused code to elaborate on.

Thanks for reading my drivel.

[Nabil]

Hehehe your post made me laugh.

I have been getting the P0400 ever since I changed my knock sensor. I don't know what I have done wrong in the process of putting the manifold and the EGR back together but I clear the code and it comes back randomly.
Sometimes it comes back when going on a bump, or when it's really humid.... I don't know.
I haven't cleaned up the EGR after that. I did clean up the what you call "snake eyes" lol when I replaced the knock sensor but that's about it.

I might take the EGR valve itself later on this summer and clean it thoroughly.
I also get a code for the solenoid mounted on the IM. That one is not so often though.

[bjwagner@uwm.edu]

What year is your car Nabil? I get the same codes randomly as well. The CEL light has a mind of its own so I just disconnect/reconnect the battery and clear the codes so I don't have to look at it. The last codes I got were (I think) P01525 and P0421 which was like a solenoid valve and the cat converter... I might add that I JUST replaced the converters about 40k miles ago, so I'm pretty sure they're still working fine. The valve I don't really know much about, and it sounds expensive to replace so I'm just going to run the car as is because it's running perfectly fine.

[Nabil]

What year is your car Nabil? I get the same codes randomly as well. The CEL light has a mind of its own so I just disconnect/reconnect the battery and clear the codes so I don't have to look at it. The last codes I got were (I think) P01525 and P0421 which was like a solenoid valve and the cat converter... I might add that I JUST replaced the converters about 40k miles ago, so I'm pretty sure they're still working fine. The valve I don't really know much about, and it sounds expensive to replace so I'm just going to run the car as is because it's running perfectly fine.[/b]

Mine is 01 Milly 2.5. My brother drives the car and I gave him the code scanner so he can check the codes and delete them if any show up. So far it's always the P0400.
The other one I got sounds like P1525 but I don't remember. But it's the solenoid that responsible to open the butterflies in the intake manifold beyond 4K rpm.
So I don't think it's a big deal to change it. I'm taking my time on that one bu I should take out the EGR again and clean it up... I think something wrong with the gasket or I didn't put it properly... That's the only gasket I didn't change when I did the knock sensor.

Do you have hard shifting from first to second gear?

[bjwagner@uwm.edu]

Mine is 01 Milly 2.5. My brother drives the car and I gave him the code scanner so he can check the codes and delete them if any show up. So far it's always the P0400.
The other one I got sounds like P1525 but I don't remember. But it's the solenoid that responsible to open the butterflies in the intake manifold beyond 4K rpm.
So I don't think it's a big deal to change it. I'm taking my time on that one bu I should take out the EGR again and clean it up... I think something wrong with the gasket or I didn't put it properly... That's the only gasket I didn't change when I did the knock sensor.

Do you have hard shifting from first to second gear?[/b]

Yeah I'm running the same engine. '01 2.5 KL engine. I just had a ton of work done to it too. Updated knock sensor from Mazda put in so they replaced all the intake manifold stuff along with it. I also had an oil leak into the spark plug well causing some arcing so I had that taken care of at the same time too. I performed a tune up and put in some nice NGK wires, rotor kit etc. WIX fuel filter (had never been replaced before now) and I went from 19-20 MPG to 26 MPG average the last 10 or so fill ups.

I get the hard shift from 1st to 2nd gear when I'm running under like 20mph. If I'm getting on the highway etc I don't experience it. Just when I'm doing a lot of stop and go driving, which I try to avoid. I'm guessing you have the same problem? Have you replaced the solenoid valves at all? I'm looking at taking care of this problem and hoping it clears up my code problem. I know those CATS are firing off properly. How easy was it to clean the EGR valve for you?

[T2T]

How easy was it to clean the EGR valve for you?[/b]

To properly do the job, you'll need to get 2 gaskets. 1) is a metal diamond-shaped gasket for the EGR valve, and 2) is the throttle body gasket. Both of these items can be purchased from either the dealership or an import car parts store. I've actually found that the dealer's parts prices for the items isn't too high. To save money on the 2 gaskets, go through Rock Auto - if you can wait a week or so for the parts to arrive.

The work:

1) Remove the air intake hose from your throttle body and the air box. Set it aside.

2) Remove the 2 nuts and the 2 bolts that are holding your throttle body in place.

3) Slowly slide the throttle body by tugging on it until it clears the top 2 studs and then set it down and out of the way.

4) On the back of your engine, remove the 2 bolts holding the EGR valve in place.

5) Carefully mark the two rubber hoses that connect to the EGR valve as one of them is a coolant hose. Then, remove the hoses so your EGR valve will be freed.

6) Thoroughly spray the EGR valve with carb cleaner to knock the carbon loose and use a small brush to clean additional deposits off as necessary.

Move onto your intake manifold.

7) Look into your round intake port. You'll see 2 "snake eyes" which are slightly raised, but do have holes in them.

8) With some flexible copper wire, ensure you loosen up any carbon deposits that may be present in these holes.

9) Retrieve your trusty can of carb cleaner with the red flexible "straw" connected to the sprayer.

10) Insert the straw into one of the snake eyes and and spray like crazy. You should then be able to reach around to the back of the engine and feel carb cleaner being ejected from one of your EGR ports.

11) Move the straw for the carb cleaner to the other opening and again, spray like crazy and ensure the fluid is being pushed out through the back EGR port.

12) Let the carb cleaner evaporate / dry up a bit for a few hours.

13) Reassemble your EGR valve using the new gasket.

14) Reassemble / install your throttle body using the new gasket and the 2 bolts and 2 nuts. When you install the bottom 2 bolts, ensure you've connected the 2 devices that should connect under the bolt head to be held in place. I believe one is a ground wire with a ring on it and the other is metal support for your throttle linkage.

15) Install your air intake tube between the air box and the throttle body.

16) Clear the engine code with a code reader.

17) Start your car up and check for any vacuum leaks around the EGR valve and around the area where the throttle body was removed. If none appear present, take your car for a test drive.

18) In the days and miles that follow, hope, pray, whatever, that the check engine light doesn't come back on. The P0400 could reappear. Or, if you've cleaned up the EGR passage thoroughly enough, a different code could be possibly set as one works on narrowing down the true cause of the P0400 code. Or, maybe your vehicle was just one of the lucky ones - and cleaning the EGR passages removed the P0400 error code and that's it.

Best of luck.

[Nabil]

Oh T2T thanks for the tutorial!! It really cleared things out for me.
I didn't replace the EGR gasket when I cleaned it last time but I did replace the throttle body one. Should I replace it again? It's not that old... Probably around 4 or 5 months.
I didn't change the EGR gasket coz I thought it's metal and no need to change it but this time I will.

There is a bolt on the bottom of the EGR that is PITA to remove. It took me almost 2 hours of removing it when changing the knock sensor 5 months ago. Thanks to Xedosman tutorial on that it was great

I think after cleaning the EGR, you should check it by blowing or sucking air from it while car is running... I forgot how to do it but it's here somewhere in this forum. It might be that the EGR does not function correctly.

Btw, the butterfly valve solenoid, does it have to be Mazda? I mean can I use another solenoid from a different car? If it doesn't bolt in there, maybe I can just zip tie it. They are kinda pricey.

Also, waiting for the carb cleaner to dry, wouldn't leave deposits in the manifold? Since the liquid is carrying deposits with it, I think it's better to assemble and turn the car on and have it suck all the carb cleaner in there with the deposits to burn them all... Just like if you are seafoaming.

My VCG's need to be reaplced too specially the rear one. The rear one is leaking oil and I smell it when the car is hot. Outside and sometimes through the AC. Not cool.

Milly_01, yeah I do have the hard shift. And it is very annoying because my engine mounts seem to be destroyed. There is a lot of engine play when I put car in gear and change from D to R and vice versa. And if I redline the car on first gear and second gear, the car will not shift into 3rd gear!! The rpm's will just fly and it will act like if the car is in neutral... Until I leave the gas pedal, then 3rd gear comes. Weird and it sucks so bad when you are merging on the highway.

[T2T]

I didn't change the EGR gasket coz I thought it's metal and no need to change it but this time I will.

There is a bolt on the bottom of the EGR that is PITA to remove. It took me almost 2 hours of removing it when changing the knock sensor 5 months ago. Thanks to Xedosman tutorial on that it was great [/b]

I didn't recall the year of your Millenia. Mine is a 2002. I have just 2 bolts that hold the EGR valve in place - both are horizontal (across from each other) on both sides of the EGR valve.

In regards to replacing the metal gasket, I tend to prefer to replace it now each time I have the EGR valve off. The gasket runs about $9.00 at the dealership, or $3.50 (or so) at Rock Auto. The metal gasket isn't fully flat when new - it has a slightly raised / beveled portion around the two larger EGR ports - it sort of forms a figure "8" design. I sort of consider it cheap insurance - especially if the EGR valve is such a hassle to wrestle with the get back in place.

One time when I cleaned the EGR myself, I reused the gasket. However, I had some silicone sealant which indicated is was O2 sensor safe (apparently, silicone can cause issues with O2 sensors failing). I used the sealant on both sides of the metal gasket. A few months later, I had my car in the shop so they could perform the $250.00 BG Products EGR cleansing process. The mechanic clearly labeled on my final invoice that silicone shouldn't be used for sealing such components.

So, now, I've moved onto Permatex High Tack gasket adhesive. It's good for up to 500 degrees and forms a very nice bond to gaskets and other materials that you mate it with. It takes only a few minutes to get super tacky and 3 hours to fully cure.

Finally, in response to your comment regarding getting the car up and running to burn out the carb cleaner, that seems like a legitimate idea. I was basically cleaning mine on a very hot day and ended up combining a break while allowing some of the fluid to dry out at the same time. Once I had the carb cleaner flowing nicely through the vents to the EGR ports, I assumed all was nice and clean. I got a bit lazy and didn't want to power up the 26 gallon compressor that tends to shake my garage when in use - otherwise, I would have applied a nice stream of air through the EGR holes to push out the liquid through the snake eyes on the intake manifold.

Whew. Sorry about the long-winded responses.

[Nabil]

Mine is 2001... I remember it had 2 bolts one on each side around the middle of it or something. But then, the EGR itself it mounted on a tube that runs from the exhaust. On that tube, the EGR is held in place by a very rusty/stuck nut. I had to spray it with WD40 and wait for awhile then spray again and wait. It wouldn't come off and I almost stripped the outside. At that time I didn't have that kind of plier that actually can hold on to the nuts. Idk if you recognize the plier I'm talking about. If I had it, probably it would have been easier to remove the nut.

Oh the point is, if you wanna clean the EGR and need to take it all out, you have to loosen that nut. Otherwise, it will be hanging in place and you can clean it while it's still behind the intake manifold.

Or you know what, maybe that nut I'm talking about is not connected directly to the EGR... The tube might be connected to the IM not to the EGR... I honestly forgot lool

[T2T]

The countdown begins ...

Hopefully, I've corrected the P0431 code by using the spark plug anti-foulers in conjunction with my O2 sensor. I should know within the next 50 miles or so if the CEL doesn't come one for that code.

While I had my code reader connected to reset the CEL light after finishing the work this evening, I also realized the P0400 code has re-appeared. I tell you, I get no respect with that code. I'm out of ideas on my attempts to resolve it for good.