P0401 again
 

I'm getting a P0401 again. I took the EGR off today and cleaned it. Looked pretty good and wasn't really very dirty.

Not sure if I need to take off the TB and clean the ports up to the SC. I tried a test I read about, I took a 9 volt battery, connected it to the outside leads of the EGR while the engine was idling. I could hear the EGR click and the engine started to run very rough but didn't stop running. Makes me think that I can't be completely clogged if it is carbon.

This diagnostic was in regards to a 3.1 and the engine was supposed to stop running. Any thoughts on my next steps and if anyone knows should a 3.8 stop running on idle when the EGR is opened?

Take a look here.
https://www.gmforum.com/showthread.p...82#post1390970

Running rough when you open it suggests to me a vacuum leak.

See the below link. Running rough when open is normal or it should even stall out according to the below.

http://www.wellsmfgcorp.com/video_egr_hq.html

OK, I see what your doing now. Opening the valve like that opens the system to the exhaust letting in unmetered air, ie, a vacuum leak. I misunderstood your first post a bit.

I've been having this code a lot too. Even after my adventure the previous couple weeks.
So- I decided to pull the EGR like you did and was surprised at how clean everything was. So I doused and cleaned it all up, plunger moved freely- like I said, did not see the buildup I was expecting.
Reinstalled the valve and plugged it up- did some short driving runs and no codes coming up yet. I did notice it popping when I first started it up (popping meaning, I could hear the solenoid activating).

fwiw- since I got my scanner- I've helped out 4 friends with their car! and then fixed em all themselves!

It don't take much to disrupt the valve movement. Sometimes you may need to clean it more then once to make sure.

Spoke too soon- back again.

A crack in the EGR tube can also cause this code. It's also hard to find by simply spraying carb cleaner around it. Pulling to tube and looking for light leaking is the best way to find the leak. The cracks show up under the clamp most of the time.

Hang in there a second.

Dan.. are you saying that a cracked EGR tube may cause this code? Wouldn't that be a too much flow or lean code instead of a insufficient?

The name of the code not being listed in the thread is a detriment to the thread.
P0401 EGR SYSTEM INSUFFICIENT FLOW

Here's the GM FSM info on the code.
http://gearchatter.com/viewtopic9016...f22f51cf703f80

I've seen many guys spin their wheels checking the EGR etc because EGR is named in the code. The problem is usually not an EGR though. The system reads the flow at the MAP sensor. If the MAP doesn't see a change in flow as it's expecting when actuating the EGR, it sets the code. Please check your map sensors and the vacuum lines going to it if you are supercharged.

Thanks for the info. My bad, I did not realize that the code didn't automatically reset after I cleaned the EGR so I will disconnect the battery or borrow a scan tool to reset the code. If I still get the code I will start to review the steps you've listed such as looking at the map sensor. I don't think this is a cracked pipe as I should start running rough but I'll leave all options on the table for now. The engine is running great, no rough idle and I had replaced most of the vacuum lines when I did the lower intake gasket.

Definitely have a good look at all your vacuum lines. Vacuum leaks will throw this code because the PCM as stated, commands the valve open on deceleration while running the diagnostic, and expects to see a loss of vacuum as reported by the MAP sensor. If you are already leaking vacuum somewhere else, opening the EGR won't cause enough of a change and you'll get a P0401.

Vacuum leaks will cause a lot of diagnostic issues on modern automobiles. Been there, done that... the hard way. :)

Since the car is running good it has been low priority but I plan on looking at the lines around the map sensor this weekend.

Ok, Got it fixed. Turned out it was one of the vacuum lines I replaced when I did the LIM. All the connectors on the lines were brittle when I did the LIM and I could only find a universal T for the three lines that connect in front of the SC. One of the lines had slipped off one ridge on the connector and must have been leaking only slightly. So after jamming it very hard over the ridge of the connector the code went away! I may go back to the factory connectors as it is a cleaner setup but all is well now. Focusing on the MAP sensor and working back through the lines did the trick. I would recommend looking at the lines connected to the MAP sensor on the P0401 code troubleshooting section (https://www.gmforum.com/obd-ii-trouble-shooting-153/p0401-284082/) and also, the 9 volt battery trick to check if the EGR valve is working (http://www.wellsmfgcorp.com/video_egr_hq.html) and also put the link http://gearchatter.com/viewtopic9016...f22f51cf703f80 that Bill Boost provided in the troubleshooting section also. Thanks for all your help!

Glad you found it. As I suspected, a vacuum leak. I just had to replace about 3 fittings on my Bonny. The tee from the fuel pressure regulator, the adapter at the SC boost solenoid and the tee in front of the SC where yours was leaking. BTW, I've also had those hard line sections get brittle and crack.

Vacuum is oh so important nowadays. I suggest hooking up a vacuum gauge when you know it's tight so that you can compare it further down the line to see if you have a leak somewhere. It will immediately tell you if you have a true leak or a MAP sensor that's lying to the PCM.

GregB

Hi Greg, Did you use the factory fittings when you replaced the lines? I had went to the dealer but they couldn't find the part numbers for the factory fittings. I looked at Rock Auto and couldn't find them and the couple of parts stores I went to had limited supplies of fittings.

The big thing on the info I posted is that...even though you see EGR in the code description, it's not necessarily an EGR issue.

Good point Bill. When I did search the posts and also found the info on P0401 I didn't find a lot of info on specific troubleshooting steps or specific causes so I was thinking it might be helpful to add more to the doc. I think the site is wonderful and has helped me greatly.

I didn't have to replace the hard lines. They broke right at the rubber fitting and there was enough slack to push them securely into a new rubber fitting. I got the replacement vacuum fittings at the local Auto Zone, but they rotted within a year and a half, and I just replaced them again. I have seen that small hard line in the auto parts store even though it's not custom bent. You could probably form it using a heat gun if you really wanted to. I've done that with other kinds of plastic tubing.

GregB