EGR Modulator failure mode question (1 Viewer)

[CharlieS]

Hi all,

EGR modulator question. I read the FAQ and did the archive searches. I don't have a FSM (yet) - I am ordering one from CDan any day now, I want to make sure I get all the parts I need for a deferred service session before ordering it.

I just recently got my '96. It was throwing the PO401 code (Exhaust Gas Recirculation Flow Insufficient Detected).

I'm wondering how I can tell if my EGR modulator has failef? Other than the carbon buildup seen in the FAQ are there any troubleshooting steps? Or is R&R the oly troubleshooting possible.

I've reset the OBDII several times and the PO401 code keeps coming back after a bit of driving. The EGR valve was replaced by the PO (I have the reciepts) within the last 20K miles - dealer told him that was the problem. It wasn't.

After reading around the site here, I got to thinking it was probably the EGR modulator clogged with carbon. This made sense since I have the "bad" green top modulator.

However, when I removed the modulator and took off the top and filter media, I didn't find any carbon buildup at all. I was surprised, thinking it would be like the nasty picture on the FAQ. Mine was completely clean (except a pinhead sized black area on the filter media).

Can the modulator fail internally and not have that carbon buildup? Is there a diaphragm or something that may have worn out but not be visible?

Are there any tests for the modulator? Or should I just update it to the blue modulator as preventitive maintenance?

I was hoping the fix would be simple and I wouldn't have to get into the VSV.

I'm getting kind of sick of the check engine light.

The more I read this site, the bigger my first CDan parts order gets...

Thanks,
Charlie

 

[Beowulf]

Test, then replace the VSV for EGR if it is defective.
-B-

 

[Landpimp]

there isn't much in the modulator that can go bad, I doubt thats the problem.

 

[CharlieS]

Thanks guys, I did a different search and found more info. Sorry to post such a newby question. I must've been looking with the wrong search terms.

Thanks!!!

Also, the PO didn't replace the EGR valve, he replaced the PCV valve and grommet. Stupid me.

For anyone else looking try searching on "VSV" and you'll find more info and even info on testing the modulator.

Looks like I need to order a VSV for EGR, EGR modulator and maybe even an EGR valve from CDan. Ack.

Charlie

 

[semlin]

nope, I wouldn't order any of those things yet. Have you checked all the vacuum hoses for carbon blockage? Have you verified that the throttle body ports are not blocked? I would verify those things first and also clean out the passage in the air intake plenum between the EGR valve and the air intake. You need to pull the egr valve and the throttle body to do this and to be safe you will want to buy the gaskets for both, although you will probably be able to reuse the old ones.

If that doesn't clear the code then you can start replacing parts. Your modulator sounds fine, so unless it fails the test in the FSM I would start with the VSV.

 

[landtoy80]

I think you should upgrade to the new modulator.
Even if its good now it WILL fail at some time and carbon will get in your system and damage the VSV.
Think of it as replacing the air filer, you don't wait for it to fail before you replace it.
BUT this is just me, I would rather replace something now, at home than have it go bad in the middle of a WI swamp (those cranberry gators are deadly)

 

[dd113]

EGR temp sensor can also cause a code 401. There is a resistance test but the part is cheap.

 

[Rookie2]

My P0401 like many others, was the VSV for EGR. Although I also had replaced the modulator per Landtoy's recomendation (that wasn't it though). Just how much of a cut does C'dan give you from those modulator sales

 

[landtoy80]

Replacing a bad modulator will not FIX your egr code problems.
Once there is any carbon in the system, it can get stuck in the VSV and cause problems.
I took a pic of the guts of the VSV but my camera doesn't like closeups.
Its a electro magnet with a diaphram and a tiny spring. The ports are very small in it so any carbon can plug it.
The VSV could fail do to worn spring, hole or crack in diaphram or other unkown reason.

I don't get kick backs from Cdan.
I bought stock in the Mitakachitonu corp. (they make the NEW modulator)