P0401 trouble code

1996 3.4L V6 5VZ-FE

I'm getting a P0401 code, exhaust gas recirculation flow insufficient detected. This is a recurring problem. I'm dropping my truck off at the shop in the morning for other work, so I'd like them to diagnose this too.

In 2020 I got the code and replaced the EGR vacuum modulator. That seemed to fix it. I also replaced lots of vacuum hoses.

At some point I think cleaning or replacing the gas cap seemed to fix it.

For months and probably years the EGR port just inside the intake manifold has been completely sealed shut with carbon, which I would think would stop the EGR system from functioning, and yet the code goes away for months at a time.

I was trying to get some stuck nuts off the metal pipe attaching to the rear of the EGR valve, to remove the EGR valve and clean that carbon out, and I finally got the nuts loose but in the process I had tried hitting them with a butane torch. I tightened on new nuts because I needed to tackle removing that pipe on the exhaust manifold and have new parts ready before I do, so I have not removed the EGR valve yet. Might have fried the EGR valve with the torch?

This month I replaced a solenoid valve that the PCV valve hose goes to, because I snapped it while removing air hoses. Twice actually, and I'm on my third one. I think it's an idle up AC valve but I can't find much info on it and it doesn't look like it's connected to the EGR system at all.

One problem is the EGR valve 25620-62060 is discontinued and is nowhere to be found from dealers, ebay, auto wreckers, and I've seen no aftermarket part that looks the same.

I just cleaned the gas cap and could clear the code and go for a couple drives again tonight, but I'm dropping it off at the shop to inspect this and do other work in the morning, so I don't know if I should be clearing the code now and risk not doing a full enough drive cycle to make it come on before going to the shop, causing them to see no problem.

The gas cap is new and has a good gasket, and I cleaned the hole where it goes, but the rim of the hole is rough feeling and might not be giving a good enough seal, even though it does suck a tad bit of air when I remove it, suggesting a seal. However the timing here is doubtful given the EGR work I just tried doing, and I don't know if this the gas cap would have anything to do with it.

Is the shop likely going to be able to diagnose this? Are they typically able to do electrical testing of all the EGR parts and vacuum testing of all ports? Should I give them the P0401 troubleshooting pages I copied out of the FSM? It's not the dealer, just a local shop.

Pretty concerned because I'm due for a smog test in a few months. That does give me time to have them ignore it if prudent for now and then I'll clean out the EGR and pipes when I get all the parts in (gaskets, nuts), and go from there.

Edit: I just changed out all the small vacuum hoses with OEM hose, in case there was a leak. I found a drop of liquid (water?) in the hose connecting the EGR vacuum modulator and EGR valve.

 

there are provisions allowing for a smog exception if the part needed to “fix” the car are no longer available. How much of a pain is it… dont know. You will have to contact your states controlling authority.

 

Interesting, I didn't know that. I'll look into it if it comes down to a bad EGR valve. My understanding thus far is the EGR valve rarely goes bad and it's usually the EGR gas temperature sensor, EGR VSV, a vacuum leak, or carbon clog.

 

https://www.smogtips.com/smog-question/4132/What-Can-I-Do-If-My-Car-Has-An-Obsolete-Emission-Parts

not sure what state you are in.

 

Yep I'm in CA and that looks like a CA program. I'll keep it in mind, thanks!

 

Vsv is common culprit for that code. Had that code when i bought truck and after checking egr valve found it was vsv.

 

I have this same code, please check out this guys video. It takes a complex system and allows you to trouble shoot before throwing parts at it. I narrowed mine down to the VSV and the part is on its way. Good luck
https://www.youtube.com/watch?v=cvo1e4JcfSY

 

I had a shop fix it a year ago and break the new PCV valve twice in the process and leave me with a broken one. It was the VSV. I had noticed that the EGR valve was completely clogged up before that with carbon and wasn't even giving a code to complain about it.