EGR P0401 That will not go away

I have this DTC P0401 that continues to plague my '96 3.2L Rodeo that will not go away. I replaced the EGR since it had such a build up of carbon that cleaning would not be practical. I also have two new cats and pre-cat O2 sensors since they were popping codes and the truck has 162k on it. I cleaned out all passages including the pipe to the exhaust manifold. I pulled the throttle body and don't see a pipe running through the plenum and intake manifold. I checked the FAQs and only see some info on how to clean '98-on motors and still can't determine if it has the same setup or not. I know those motors are a bit different. If I pull the EGR off then start the motor, the RPMs shoot up rapidly, leading me to believe it is not clogged. The EGR is an aftermarket Delphi and I continue to read how these Rodeos prefer factory parts. My next step is to try and get a factory EGR and see if this will remedy the problem. Any suggestions??

Delphi IS factory. You've still got some sort of blockage somewhere. You may have to remove the throttle body to completely trace the entire path of the EGR system.

Your blockage is most likely between the EGR and the intake. Usually right where the passage exits into the intake or throttle body.

Try to shoot some compressed air down the pipes.

What happens if one just leaves it alone??

Seriously...I have the same issue that's been on going for quite some time. I flat gave up, Rodeo still runs just as good. But...will it hurt it in the long run?

What happens if one just leaves it alone??

Seriously...I have the same issue that's been on going for quite some time. I flat gave up, Rodeo still runs just as good. But...will it hurt it in the long run?


Actually, it could cause damage in the long term, although unlikely, as well as making the engine run less efficiently by causing the timing to be retarded when the PCM detects more frequent spark knock. Also, if he has to pass an emissions test where he lives, the car won't pass.

The EGR system is actually very simple. It is simply a passage from the exhaust back to the intake. The passage is controlled by the EGR valve which is controlled by the PCM. When the PCM commands the valve to open, it expects to see a change in the O2 sensor readings. If it doesn't see that change, it can only assume that the EGR passage is blocked or the valve isn't working. EGR is just a very easy way to reduce NOX emissions which is caused by high combustion chamber temps. The recirculated exhaust gas lowers the combustion chamber temps keeping NOX in control and helping control pre-detonation or spark knock.

So...is it unlikely?

I don't know where else to look, honestly. I've cleaned the tube out as much as I could, replaced the valve, etc. the code still comes back.

CEL goes on and off quite often, always the same code.

That is what I thought. Delphi produces for Isuzu and GM. One suggestion from a mechanic was to pull the EGR off, start the engine, wait and see if the RPMs shoot up rapidly. He claims that if they do, then there is possibly other causes. After searching the FAQs on cleaning the passages, I can only find '98- motors. I've pulled the throttle body and don't see a pipe running through the plenum like you do on the newer models. Is there a tube that runs through the intake man. on this year? Damn these engines are messy. The truck runs like a beast though.

What happens if one just leaves it alone??

Seriously...I have the same issue that's been on going for quite some time. I flat gave up, Rodeo still runs just as good. But...will it hurt it in the long run? Have you pulled the intake off and cleaned in there or looked for an extension of the piping?

Is it necessary to disconnect the neg. cable for 15min and put back on in order to reset the onboard diagnostics? Did you do that?

Matan**,clear the code??? Come on buddy, looking for some realistic diagnosis.

No, I haven't pulled the intake, for one, everything I've read says that it won't do serious damage and the fact that it runs so good otherwise, I haven't seen the real need to do so.

But..if it does cause damage, then I'll look into it. I've meticulously maintained this beast, and out of everything I've read, everyone's been able to clear this code without taking off the intake.

That is what I thought. Delphi produces for Isuzu and GM. One suggestion from a mechanic was to pull the EGR off, start the engine, wait and see if the RPMs shoot up rapidly. He claims that if they do, then there is possibly other causes. After searching the FAQs on cleaning the passages, I can only find '98- motors. I've pulled the throttle body and don't see a pipe running through the plenum like you do on the newer models. Is there a tube that runs through the intake man. on this year? Damn these engines are messy. The truck runs like a beast though.
I had this problem too. What solved the problem for me was to take the EGR off -- spray carb cleaner down the passages and then start the engine. The gunk and carb cleaner will expel (you may seem some flame -- stand back!). Clean everything again and replace EGR.

Wreck,
I've tried cleaning everything(passages to the throttle body and tube running to the exhaust manifold). No luck, the code keeps coming back.

I am getting a P0440 code now along with the P0401. I can see from the schematics that the EVAP canister vent solenoid and EVAP canister purge solenoid are related to the EGR in terms of vacuum lines and/ or system. Is there a connection here? Leak in the canister/line or vacuum leak.

Wreck,
I've tried cleaning everything(passages to the throttle body and tube running to the exhaust manifold). No luck, the code keeps coming back.
I may not have explained it very well. What was happening to me was I would get the EGR cleaned out very well with carb cleaner. I would then clean out the actual passages. When I would replace the EGR and start the engine -- the carbon build-up that I attempted to clean would re-foul the EGR valve and thus defeat the original cleaning. I'm saying to let the motor rev (with the EGR off) for awhile to let the passages clear up. THEN, clean the EGR valve itself again (and around the gasket). Replace the EGR, unhook the negative battery cable for 15 minues before re-starting again. You should see enhanced engine performance and no return of the code.

I had this problem too. What solved the problem for me was to take the EGR off -- spray carb cleaner down the passages and then start the engine. The gunk and carb cleaner will expel (you may seem some flame -- stand back!). Clean everything again and replace EGR.

Wreck,
You explained it just fine. Cleaning it any further is not resolving the problem. It needs a real deal scan to gather some more data on the EGR and EVAP systems. I have a scanner that will give I/M readiness, heated O2, MAP readings, certain temps, , but I want to see more. There is more than just a blockage. The chk/eng light went out the other day without clearing the code. I checked some of the vac lines and the hose from the valve cover to the throttle body or additional PCV was split open. I replaced it and the chk/eng came back on. There has got to be some vacuum leaks.

I may not have explained it very well. What was happening to me was I would get the EGR cleaned out very well with carb cleaner. I would then clean out the actual passages. When I would replace the EGR and start the engine -- the carbon build-up that I attempted to clean would re-foul the EGR valve and thus defeat the original cleaning. I'm saying to let the motor rev (with the EGR off) for awhile to let the passages clear up. THEN, clean the EGR valve itself again (and around the gasket). Replace the EGR, unhook the negative battery cable for 15 minues before re-starting again. You should see enhanced engine performance and no return of the code.

Ditto...I've attempted all of this over and over and over at least 6-7 times...it's as clean as I can get it, even the butterfly, and the EGR valve and gasket were replaced over a year ago. Still get the code back at least every other week, it'll last a few days then go away and come back.

Everything people have mentioned, I've tried and done several times. I don't know what gives :crying:

The only other thing I can think of is that the EGR valve isn't opening when it's supposed to. If the EGR valve isn't defective, then the defect has to be in the wiring going to the EGR valve. It's the only other thing it can be.

One of the things I checked when I first started getting this problem was the wire plug going to the EGR. After replacing the part, I noticed it was little taller than the old one and stretched the wire to the point where it was completely taut with no play. I thought this might be compromising the connection. Anyway, I going to have to send this one to my mechanic. Emisson test has to pass.I will update the prognosis and maybe it will solve the problem for your truck(s) too.

Sorry I can not offer any solutions, but I can offer up what I have tried that has NOT helped. I've been dealing with A P440 error and a hard shift issue for 15,000 miles now (a bit over a year). 1) tried gas cap. 2) tried cleaning EGR tubes. 3) Replaced EGR valve. Took to dealer. 1) Dealer replaced my new gas cap with their new gas cap. 2) Dealer replaced gas tank filler neck. 3) Dealer replaced purge solenoid ($600). 4) Dealer replaced "kinked" hose over transmission. And now $75 miles after this last "fix" I'm back on line looking for an answer. Please let me know if you hit on a solution, I've ordered a used ECM to see if swapping it changes anything.
B
PS If anyone hits on a solution for a slam shift that happens in mostly below 40 degree weather and does it on up and down shift. I's love to hear the answer. I have replaced Transmission Position Switch (even though it did not have the same symptoms as I've seen here) and Throttle Position Sensor. hope the ECM might have an effect here as well....:confused: