P0401 to P0402 / 96 Explorer 5.0

[ejscarfo]

So I've been battling with the CEL for sometime now on my 96 XLT 5.0. It comes and goes and its always been the same code, P0401 (low EGR flow). I checked the vacuum lines and the little rubber hose coming from the EGR Pressure Feedback Sensor into the EGR valve was brittle and looking mighty homely, so I changed it, cleared the code and after a day, it came back. I decided to remove the EGR valve and replace it with a used one I had in the garage. It was easy to get off btw using stubby racheting wrenches (getting the bottom nut back on was another story). I inspected the used valve, it was clear of carbon deposits and the EGR position sensor on it looked like it was brand new. I installed it, connected everything back up and took it for a ride. The CEL light came back. I pulled the code and now its a P0402 (too much flow). I'm thinking the problem is lying either with the position sensor or the feedback sensor. Any thoughts guys?

 

[jremington59]

I have the same engine and had the same problem.

I'd change the positioning sensor if you've checked everything else. My problem was the gasket between the sensor and the egr itself.

 

[ejscarfo]

I have the same engine and had the same problem.

I'd change the positioning sensor if you've checked everything else. My problem was the gasket between the sensor and the egr itself.

There was no gasket between the two on mine, I checked. Is there supposed to be? The gasket was for the EGR itself, which I changed.

 

[jremington59]

My problem was there was no gasket between the two.

http://www.explorerforum.com/forums/showthread.php?t=259697

There was a wives tale that it increased the HP by removing the gasket. I have had another person find the same thing on theirs. There is supposed to be a gasket between the egr and the sensor.

I see you live in NYS also.

 

[ejscarfo]

Yup, NYS, on Long Island, and I need this fixed to pass inspection at the end of the month. I just bought a new position sensor and lets see if it comes with a gasket. There was a sort of gasket there, like a plastic ring actually. Is that what we're taking about?

 

[jremington59]

That would be it. Seeings you have the new sensor you may as well put that on also. But without the gasket it's going to draw air and the egr won't work properly.

 

[ejscarfo]

Thanks! Now I hope I can get the sensor off without having to remove the EGR valve again. If I can, my knuckles will thank me.

 

[jremington59]

I hate to tell you, but I don't believe you can. If I recall it's held on by three small bolts and they'd be hard to get at.

 

[ejscarfo]

You're right, I had to remove the EGR valve again, but its ok, I'm a pro at it now.

Well I got the new positioning sensor and installed it this morning. I put everything back together, checked to see all was connected, etc. and cleared the code. I let the truck warm up and the light stayed off. I took it out for a quick drive, light stayed off. Great I thought, right? I went out later on to the store and the stupid light came back on. I parked, whipped out the scanner and wouldn't you know it, P0402 again. WTF now!? Does that sensor need to be adjusted? Any ideas where too look for the problem? I mean from low flow I go to too much and all I did was clean the EGR valve.

 

[jremington59]

You did put the gasket on right? And the gasket for the egr on the engine?

There's one other part it could be. I can't recall the name but it has the T on it and the vacuum hose goes to it. I'll have to look up the name of the part. And lets not forget it could actually be the egr itself but that isn't usually the case.

 

[jremington59]

The other part is called a EGR Vacuum Solenoid. It costs like 25.00.

The more I think about it going from one code to another is if it could be the valve itself....... It's just one of these things that drive you crazy.

 

[ejscarfo]

Yup, I replaced both gaskets, one for the EGR and one for the positioning sensor. I was thinking it could be the solenoid as well. Rock Auto has one listed but the picture looks different from what I have, mine has a knob like top on it where the electrical connector goes.

I tried 2 different EGR valves. One that was used but clean, and it tested well to hold vacuum and the original one I pulled and thoroughly cleaned. With either one installed, it throws a code P0402. I'm at the point where I may just pick up a new EGR valve and see what happens. If I take it to my tech, I'm afraid what I'll get charged.

 

[jremington59]

If you have a napa nearby they have the solonoid for 25.00.

When you checked the EGR did you use your mouth and suck on it and see if it opened easily? Then did you make sure it was seating closed? As I said, it's very seldom the EGR valve.

In my readings I did come across a section on the internal EGR itself. If I recall this is under the intake manifold and can become clogged with carbon. But thats very rare. But your engine does have the internal EGR.

Now you are sure on all the vac lines correct? There's also a plastic T there that can crack. You need to check them good. If I were you I'd be getting that solonoid, and double checking everything before taking it in to the shop.

 

[ejscarfo]

I checked with Napa when I picked up the new gasket, they didn't have the solenoid and they had to order it. I ordered on from Rock Auto last night, it was cheap and should be here before week's end. I cleared the light last night and it hasn't come back, yet. It has to be something intermittent, correct?

I tested the EGR valve with a vacuum pump, it held vacuum. I also pushed up the pintle by hand to see if it moved freely and if anything was blocking the seat. It all checked out fine.

With respect to the vacuum lines, the white plastic line that goes into the solenoid supplies the vacuum, correct? and the rubber line coming from the top of the solenoid is to go to the EGR and supply the vacuum when given the signal to do so, right? Where does the white vacuum line originate? Does it come from another sensor and if so, could that be the cause as well?

I'm thinking if the code is for too much exhaust then either the EGR is staying open too long by the vacuum not being shut off or its getting hung up somewhere and staying open. Your thoughts?

 

[jremington59]

When I get a chance here shortly I'll go out and take a look at mine and see if I can help you.

 

[ejscarfo]

Awesome! It would be greatly appreciated.

 

[jremington59]

I glanced at mine and I can only see the top vac line on the solonoid. That one goes directly to the egr valve itself and it's onlt three inches long. That's also the line that has the white elbow. Does that help? If not I'll have to go out later and take off the solonoid so I can see the rest.

You want to make sure the plug on the positioning sensor and the solonoid are plugged in good.

 

[ejscarfo]

Thanks for checking.

This is what I saw when I removed the EGR. Attached to the solenoid, which I needed to remove to have better access to the bottom nut on the EGR, there is an electrical connector at the top and a rubber connector below that has 2 vacuum lines. The vacuum line at the top goes to the EGR and the one on the bottom is a white plastic line with a black plastic shield around it, almost looks like electrical wire (I thought that's what it was initially). That white plastic line has a couple of bends in it and it disappears behind the intake plenum into another jumble of wires, etc. I assume that's the vacuum feed into the switch. It has to have vacuum otherwise the EGR would not open at all, correct? I will check for vacuum when I replace the solenoid.

 

[jremington59]

Yes, the bottom line would have to supply the vacuum. There's no ther place for it to come from as the top line goes to the egr valve.

 

[ejscarfo]

The only other thing I think of is a bad or shorted connector to the position sensor. I really need a shop manual for this truck with diagnostic schematics.