I recently bought a 2005 Ram 1500 4x4 with the 5.7 Hemi. 130,000 miles. I thought I got a good deal with just a few things to fix, but about a mile down the road after signing the title, the check engine light came on. I think the guy cleared the code on me, so shame on him, but it's mine now and I want to fix it. The code is P0401 - EGR flow insufficient. When I first pulled the code and looked at the EGR valve, I realized it had been replaced recently because it was so much cleaner than everything around it (which is why I suspect the guy knew about this problem). Anyway, below is a list of what I have done so far, and the code keeps coming back, anywhere from 20-100 miles after I change stuff and clear the codes. I have:

- Pulled off the EGR valve to inspect and bench test. It is clean on the inside and opens quickly with 12v applied.

- I back probed the connector. I can tell the actuator has a good ground. I assume the power side is switched so I cant check 12v from the computer because i don't have a bidirectional scan tool. The 5v is there on the potentiometer. Ground is good on the pot. Signal wire reads something like 4.2v with the valve closed. Based on this high signal voltage I thought the potentiometer might be bad after reading other cars show like 0.8v closed. I bought a new valve / sensor and plugged it in and back probed the connector and still got around 4.2v. Unplugged new valve and returned it. Is it possible the new valve was bad? Is it possible someone did some wiring and had the sensor wires incorrect? (anyone have a wiring diagram for this valve / sensor so I can confirm my results?)

- I checked continuity from the connector to the pin that goes into the ECM for the 12v power and it was good. Checked continuity on the pot signal wire and it was also good.

- I cleaned the tube from the valve to the intake as best I could, but it wasn't that bad anyway, certainly not blocked up.

- I cleaned the EGR port in the head by cylinder 2 as best I could. Does anyone know what the passage routing is for this port? I could tell it went straight into the head for about 3 inches, then turned down towards the exhaust port, but not sure where it actually gets exhaust flow from. Does it connect to the main #2 exhaust port or pull from its own port beside the exhaust valve?

- I had my girlfriend start the truck with the egr valve removed and put my hand over the port. I could feel small pressure pulses I assume align with the exhaust valve opening, but it was less than I was expecting. But I have no baseline for such a test so maybe it is normal.

- I took the throttle body off and cleaned it while I was in there (it was really dirty).

- I took out the PCV valve and it rattled (as expected).

- I cleaned the map sensor with electronic parts contact cleaner.

- I cleaned the intake temp sensor with electronic parts contact cleaner (it has a little oil on it from the closed ventilation system I assume).


At this point I don't know what else to look at. Does anyone know what the EGR position signal wire voltage should be at open and at closed? Anyone know how much flow or pressure I should feel at the EGR port in the head at idle, or how to ensure that passage is clear? Does anyone know how these trucks determine the EGR flow is insufficient? I couldn't find anything specific for the Hemi, but I saw some generic posts that said the MAP sensor looks for a certain amount of change in vacuum when the valve is opened and it correlates that to flow. If I had a really nice scan tool I could command the valve open to check the computer / electrical side of things. I could open the valve at idle as well and see if it runs poorly. But I can't do that and really don't want to take the truck to the dealer. I want to get this cleared up and make sure everything is ok before I spends hundreds to do all fluids, plugs, and brakes. Any other ideas or direction would be much appreciated. Also any recommendations for a cheap bi-directional scan tool that will let me control the EGR valve on this truck are welcome.


Thanks for reading this far, I'm hoping someone can help and that the solution isn't a new computer.

 

Is there a vacuum port of any sort on that valve?

 

No vacuum port on this valve. Just a 5 pin connector. Based on what I've found for other vehicles, the 5 pin EGR valve is fairly common and has 12v and ground for the actuator. Then 5V, ground, and signal for the sensor.

 

Is it just a differential pressure sensor? Or is it a position sensor for the valve??

 

I think I found the problem. I have driven 56 miles of back roads, interstate, and a little bit around town without the check engine light coming back on. I also plugged in the code reader and there are no pending codes and the emissions readiness check showed everything was ready. Let's hope it stays away. If what I found wasn't the problem, then I am at a loss for what else to check. I want to show what I found in case it helps someone else out in the future. First a quick summary on the EGR system on this truck, as best as I understand it.

The EGR flows exhaust gas back to the intake, which counter-intuitively lowers combustion temps and reduces emissions. The routing of the system starts in the passenger side exhaust manifold. At the front of the manifold beside the # 2 cylinder port, there is a small passage that leads back to a hole in the head. The port in the head goes in a couple inches, makes a 90 degree turn, and then goes out to the front of the head where the EGR valve is mounted. A tube connects the outlet of the EGR valve to the intake just behind the throttle body.

The valve has a 5 pin connector. It has a 12v input from the PCM and a ground to open the valve (switched by the PCM). The other 3 wires are ground, 5v, and signal for the position sensor (potentiometer). When closed, I was getting a signal around 4.2 volts (so high volts is closed, low volts is open). As far as I could determine, there is no differential pressure sensor or flow sensor. My assumption then is that flow is determined by a change in vacuum seen by the MAP sensor. So if you are getting P0401 for insufficient flow, either there is a blockage in the lines, the valve isn't functioning properly, or the computer / sensors are incorrectly determining the flow is insufficient when it is actually fine. For each of these high level issues, there are many possible causes which I won't dive into here, but I explain many that I checked in my first post.

My issue was a blockage BEFORE the valve, which seems to be uncommon. Someone previously worked on the exhaust manifold / gasket on this truck, and they put a significant amount of RTV on the new gasket for some reason. When the manifold was put back on and torqued down, RTV was squished into the EGR passage going into the head. See pictures below. I removed the RTV plug, removed the gasket, cleaned the surface, put a new felpro gasket on, and torqued the manifold to 18 ft-lbs. Now I'm driving it and hoping for the best. This is probably a unique situation, since I bought the truck this way. If I had done the manifold repair myself and afterwords P0401 popped up, it should* have been easier to diagnose. And of course the seller didn't give me this background. Anyway, maybe this post will help someone else in the future, or at the least stop someone from gooping RTV on their replacement exhaust manifold gasket.


Here you can see the plugged EGR hole, to the right of #2 exhaust port, between the bolt holes.


Here is the RTV plug removed, and you can also see the EGR valve bolted to the front of the head. Hopefully you can visualize how the passage is routed in the head.

 

Wow... congrats on finding that one!

 

Congrats on your fix. Thanks for posting all the info. I was curious as to a cause for the code and how egr flow was determined and read by the ecm. I found your posts very interesting .

 

Why would anyone put RTV on an exhaust manifold?????

Glad ya found the fix.