I have a p0401 code on my 01 mon sport 3.0 i I thought I had my problem fixed last month but this new code came on and veh wants to stall i replaced vac sol 2x checked all hoses changed the man diff pres sensor - egr is working only problem is when I connect the vac hose to the egr it starts opening at idle and runs rough and wants to stall when I plug this hose and disconnect it from the egr truck runs fine i had alot of work done on it last month by a mech now he seems to think its the ecu telling the vac sol to sent a signal to open the egr when its supposed to be closed.
thanks for any help with this

 

Hey, Sharky.

You said the EGR valve is working? How do you know? Did you replace it or did you remove it and examine it or clean it?

Check the resistance of the terminals at your EGR Solenoid — they should be between 36 ~ 44 ohms.

Check the resistance of the EGR Temperature Sensor located right next to the EGR Valve. You have to put it into boiling water and at 80c (Celsius x 1.8 + 32 = Fahrenheit, so that's 176 degrees F [thanks, manual]) the resistance should read between 290 ~ 322 ohms.

I would think you could check for signal at your EGR Solenoid at startup, although I can find no specific test for this, it would seem to be a way to check out your mechanic's hypothesis that the ECU is sending a false signal at startup. If the ECU were bad, I would think that you'd be getting an "I'm Bad" code instead of a "Let's Blame the EGR Solenoid" code, but I could also be completely wrong about that. It's also possible that your mechanic wanted to say something besides "I don't know," which has also been known to happen from time to time.

Anyway, you've got a few areas to explore. As always, the more brains at work around here the better so let's hear any more ideas from the peanut gallery....

Let us know what you find...

 

Hi Mothman52.
My mech said he checked the egr with a hand vacuum pump and I also cheked it with a vacuum line while it was idling. The egr was closed and as soon as I added the vac line to it ,it opened and started to run like it wanted to stall. I also had it off a couple days ago and cleaned it with carb cleaner it wasn't that dirty. As far has checking the resistance of the solenoid and sensor I'm not that knowledgable when it comes to using electrical testers or checking for shorts or open circuits. I think my best bet would be to take it to a mitsubishi dealer although I'm tring to avoid a big bill and let them check it out and get back to me before starting the job. hopefully just to run a
dionostic test won't be that much. Before I do that i'll keep checking back here at the forum like you said maybe i'll get somemore ideas from the peanut gallery- Mothman52 thanks for all your help

 

Sounds like a plan, Sharky.

I suppose I'm just trying to avoid the idea of having to get a new ECU, as they are not cheap:

http://www.autocomputersystems.com/E...?showrnrattop=

Almost $500 for new, $275 remanufactured from this supplier. Haven't used 'em; just Googled to get an idea of the cost. Maybe you could do better at a Pick 'n Pull or a cruise through your local craigslist might give you joy.

I did want to address your comment about electronic testing. It might seem really confusing and intimidating, but I believe that anyone who can drive a car can understand the basics enough to do a few simple tests themselves and perhaps save themselves a bucket 'o cash. I mean, at one point, driving itself seemed pretty intimidating, didn't it?

You don't have to have a Master's Degree in electronics to understand that electricity flows like a river from its source to its destination. If you get downstream and find a dry river bed, you could surmise that something is keeping the river from flowing somewhere upstream. So you keep heading upstream until you find a tree that fell across the river (in your car's case, imagine a faulty switch; the signal no longer flows as it should across its positive and negative points). So you dig a ditch around the tree. Guess what? the river now "works" again and starts flowing as it should downstream. So there's nothing wrong with the river; the problem was the tree, or switch. Plug in a new switch and your circuit once again works as it was designed to work.

That's all a simple electronic meter could do for you — it let's you measure the river's flow, how fast it's going and how much resistance it's getting from the objects it encounters along the way. If a circuit is sending out 12 volts and you're only measuring 3.5, you know something's amiss.

I know it can be intimidating leaving the security of nuts and bolts for the scarey Frankenstein world of electricity with all its goofy symbols and nomenclature, but at least consider going there. A little knowledge in that area can tell you a lot about your beast's condition; it can save you a bundle of cash, and what's more, it can give you every bit as much satisfaction in doing it yourself as bolting on a new starter can deliver.

Think about it. And there are plenty of folks around here to help.

Stepping off my soapbox for a moment, if the vacuum tests were done and you're pretty sure that your EGR is clean, then the trouble would seem to be at the solenoid or the ECU. So on to the solenoid (we're now swimming upstream ). What happens when you disconnect the electronic connections to the solenoid while it's idling? Let's do that and see....

 

You might have a blockage in one of your lines going to the EGR valve, or possibly a vacuum leak

 

mflippen,
I had already checked all the vacuum hoses on the truck but thanks for the input sharky

 

Mothman,
I think this truck has a mind of its own. My wife called me at work today and said the truck was hard to start and was running rough when idling or stopped at a light. On sunday I did replace the manifold diff pre sensor and truck still opened the egr valve at idle and I had to plug the vacuum line to it again. She didn't drive it until today. When I came home the first thing I did was to connect my code reader to make sure no other codes came up. The only code showing was the p0401 so that was good. I found the truck hard to start also I then took off the plastic cover and removed the vacuum line that was pluged leading to the egr I then unpluged the line and connected back to the egr and truck started running better and started normal.I also noticed the egr was now in the closed position even with the vac line going to it which was good it was always open I also disconnected the electronic connections to the solenoid like you said and the egr also stayed closed its not runnig 100% still running a little rough but I'm hoping with driving it around a little bit it will even out I also erased the code now i"ll wait to see if that comes back on I'm keeping my fingers crossed I'll keep you informed over the next few days mothman thanks for all your help at least your giving me great ideas on what to try to solve this crazy problem. sharky

 

Well as the Brits like to say, make haste slowly.

Sounds promising, but my idea about disconnecting your solenoid leads wasn't that it would fix your problem but that it might better point to where your problem could be found. Obviously, the solenoid was designed to do something and if you disconnect it from the circuit and there is no change, this would lead me to suspect either that the solenoid is bad or that the signal going to it is bad. I think you said that it was tested twice and was OK, is that right?

 

Mothman
I know when you said to try to disconnect the wires from the solenoid that wasn't going to fix it. As far as the solenoid i had changed that twice the first one was put in about a month ago so since it was still under warr I put another in about a week ago. The egr valve was checked 2x. I'm now still thinking about changing the egr at least i'll start off with a new one in there. I still can't figure out how all of a sudden the egr valve closed with the vac line connected again when for the last couple of weeks I needed to plug off the line or the egr would stay open at idle. I'll keep you up to date on this issue Thanks again, Sharky

 

Sharky, I didn't think that you thought that doing what I said would fix the problem

OK, how about the EGR temperature sensor? Any thought to that being bad? The final answer to this is going to be really interesting...