Ok, got a P0400 out of the car. In fact, it seems to be throwing the code every 10 or less miles!

I understand this to mean that there is a "malfunction" in the EGR path. But not necessarily low flow (which would be P0401) or too much flow (which would be P0402).

In fact, there are nine codes for EGR trouble.

Two questions:

1) What is it really trying to say?
2) How does the system know if there is too little or too much EGR flow? How is it measured?

It seems like a simple system and I get the idea that replacement of the EGR valve and Solenoid assembly ($120 for the part at AutoHaus) would probably fix it. But I'd like to understand the system more before I proceed.

The car has 73,000 on it and I've been driving it more spiritedly the past 10,000 or so. I suspect I've blown some crap out into the exhaust manifold and some of it has passed into the EGR valve and fouled it.

 

http://forums.maxima.org/4th-generat...ing-p0400.html

Just swap in "crossfire" where it says Nissan.. LOL.

 

Take the parts off and look at them, maybe you can save some money, how hard can it be?
Look in the 2005 Repair Manual EXHAUST GAS RECIRCULATION Sect 25 - page 23

 

The Crossfire looks a HELL of a lot easier than that !

 

now you know you have an easy task... lol.. but gives some pics of basically what your looking for anyways..

 

But I SITLL want to know how the system "sees" the flow - how does it KNOW it has too much or too little?

And does the P0400 mean there is an indication of too little flow, or it is more of a "something may be wrong because...."? I just want to know, because I wonder if the problem is that a sensor is bad and LYING to the PTCM. Because in that case, replacement of the EGR valve assembly would be a waste of money and time.

 

The ECM can tell when the EGR is functioning properly by watching for changes in NOx via the O2 sensors. When you reintroduce exhaust gasses into the combustion process, in the correct amount, the level of NOx in the exhaust system drops significantly. Too much of the exhaust gasses introduced in to the intake charge and you do not get complete fuel burn causing the fuel level in the emissions to rise drastically. Too little and the NOx levels stay high.
Pretty simple actually.

 

I hear ya.. both my rear 02 sensors were "bad".. till my Crank positioning sensor fixed them.. LOL. No really.. would pop the cell at least every two weeks after a reset, and now about 2 months later haven't seen that puppy light up other than starting the car when they all light.

 

I was unaware the O2 sensors were used to judge NOx levels. So, now I know where the indication comes from, thanks.

So, since I have the P0400 code, the EGR valve could be froze in either (or any) position, since I have no code indication too much or too little flow, just that there is an error.

 

Correct, the valve is probably stuck closed with the problem you are getting. You are not getting a low flow code because the exhaust isn't changing one bit when it "opens" the valve. No flow is not considered low flow in these situations.
I am not versed in the exact unit that the crossfire uses as a valve, but often on pretty much every other system out there they just get stuck with carbon and by removing them, scraping the crap off and giving them a slight whack on the valve frees them up and can get them working again without replacement. Since you already have a new one I would slap it on. Check to make sure the passages aren't blocked off with carbon, which is also a common problem in EGR circuits.

 

Figure I would help give a bit more info for background on how the system functions.
Yes the sensor in your exhaust is called an O2 sensor, but it detects more than just O2, they usually measure 4 gasses, sometimes even 5.
Here is an article that might shed a bit more light on how the systems integrate together. Not everything applies to the crossfire per-se, but the general process is similar in all cars.
http://www.autoshop101.com/forms/h56.pdf

 

That helps! Thanks!

One thing - is it my imagination or does my car accelerate better with the failure of the EGR?

It sure SEEMS like my car MOVES better in the 2,000 - 3500 rpm range.

 

It might. If the valve is stuck closed you don't have to wait for it to snap shut when you hit the pedal.

 

That is what I was thinking, I haven't done a throttle reset in a long time, but it acts like I did!

 

Ok, I ordered a valve/solenoid from Autohaus and lost my confidence in changing it myself. (If I had a second car, I'd have tried it - been without a second car for over a year now.)

Anyway, they changed it, it was not plugged at all. Dirty, but not bad at all. The little plastic part that the solenoid moves to allow the vacuum to operate the valve was bad - mechanic says it looks like heat did it and I agree. They have seen a lot of Mercedes do this in the past.

He also said that the PTCM uses the MAP reading to determine if the EGR is opening or not in the Crossfire and it's Mercedes siblings.

Anyway, he cancelled the code, no light now and no beeping from the UltraGauge. $128 for labor and $12 for the gasket.

Glover's garage in Cumming, Georgia sure seems to know the Crossfire. (I saw two Mercedes in the yard there today, and one partner's wife drives an SLK with something like 170,000 on it.)

 

Makes sense. Looks for a slight drop in vacuum when the egr is opened, essentially a small intake leak. Guess thats another way of doing it.
Glad to hear there was a definite problem located.

 

Thanks Fellas! i popped a P400 today on my way to costco and had it scanned at Orielly's. They confirmed the EGR issue. looks like it's time to order one.

The search works fine for me.


Edited to ad. $124.00 plus $1.84 for the gasket from Autohaus with free shipping

 

It's about $100 ( with shipping ) from RockAuto :
https://www.rockauto.com/catalog/x,c...,parttype,4968

( The AirTex one includes the gasket )

 

I know this thread is ancient but I'm hoping some of you are still on here.

I also have had the CEL on due to a P0400 code so I replaced the EGR valve but the P0400 persists after clearing the codes.

I'm wondering if this can be caused by a leaky hose (mine look to be in fine condition) or an O2 sensor.

 

How many miles on the car? THat code is most usually an indication of little or no flow. WHat did the passages look like when you change the valve?

Is there 12 volts on one pin? If the ECU is telling it to open, you will have 12 volts on one side and zero on the other. IF you have zero on both sides, the B+ feed to it is not there, ya gotta fix that.
If you have 12 on both sides, you have good power but the ECU (at that particular time) is not asking it to open.