How does the EGR 'sense' insufficient flow (P401 code)??

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Baxter,

Read RavenTai's post on referenced in Post 54 here. There is a range where the EGR has no vacuum during normal operation to prevent loading up the engine on light throttle. That may be what you saw.

Raven - you've got a PM..

DougM
 
Thanks Doug: I gathered those were the readings that he got during his tests, but are they in line with what the FSM calls for? Do they give figures?
I did well to find another vac sorce then as i got less than 5" throughout on my tests.
 
For Doug:
TB.webp
intake_dirty.gif
vsvr.webp
 
more, these are general Toyota and have a different layout than the 80 but schematically usable.
EGR.webp
EGRb.webp
 
CJF said:
Lots of good info as usal Beo, but I still haven't gotten one single person other than Dearborn to say they they've even replaced one period, let alone whether it did/didn't solve the problem.
Click to expand...

Conversely....

Not one single person (other than DD) has replaced their EGR temp sensor and most have eventually solved their P0401 anyway. (Not counting Bear80's cheat.)

-B-
 
B-
Respectfully, I have read a lot of P0401 threads, which is why I haven't tried harder to solve my CEL problem. From what I have read, even after people tear their hair out and throw replacement parts at the issue, it is still not resolved. They just settled in for that romantic glow thrown by the CEL light on the dash, or bypass it. I don't think we are going to resolve this anecdotally. There are a few on this thread that said they fixed it for a reasonable amount of time/distance, but I gathered that was partially due to driving habits.

I trust that Raven, you, and Doug have the competence and process to figure it out, so I'm hovering to find out what you discover. I'm happy to be a guinea pig, but I don't have a lot of experience with testing, etc. I trust the mud community and follow directions.
 
MDarius said:
.. From what I have read, even after people tear their hair out and throw replacement parts at the issue,
Click to expand...

You can add me to the list of hairless people throwing parts at the P0401. Mine failed about 3 months after I bought the truck in 2001 with ~98k miles. I cannot recall the order but I removed and cleaned the EGR valve at least twice. I cleaned the EGR modulator, EGR temp sensor, running the FSM tests over and over. I bought an OBD-II scanner to make code clearing and testing easier. I bought a new (blue) EGR modulator and replaced the green-top. I put on a new EGR valve. I cleaned and tested the EGR temp a few more times. Each time it tested fine and, in reality, it WAS fine; even when it was "dirty."

Finally, after about 18 months, the failure became solid. 2-trips & a light... every time. I yelled "uncle" took it to a trusted Toyota mechanic. He pulled out his Toyota Tester, hooked it up and said "the VSV is bad." Ordered a new one, R&R, and 6 years later it is still working fine. (disclaimer: Results not typical.)

As I have said many times, it is a simple system and not rocket science. The P0401 can be fixed though sometimes the FSM tests will yield "false negatives" meaning the VSV failure is intermittent.

-B-
 
Raven,

Thanks - that clears up another mystery port for me. Nice diagrams and such.

DougM
 
I hope I don't have to through all the parts at P0401. Just got my new vsv this evening from Dan. I'm itching to install it this weekend (tomorrow) but going to keep it locked in my parts drawer for now, at least until I get the orange CEL again. I've been dealing with the P0401 for past few days after finishing my HG. I have got used to seeing it every day. Then last weekend I did this. After that it showed up only once on Sunday morning after the engine reached normal temperature. Ever since no CEL. I am starting to believe that in my case, the cracked EGR (to Intake) hose caused the intermittent failure to the VSV. It tested out fine (per FSM) after I got and cleared the CEL few days ago. I know it may be too early to draw any kind of conclusion here but I'm gonna be optimistic. As soon as the CEL shows up again, I am going in :D.

Peace :cheers:
 
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Riad,

FYI the VSV can be removed in about 15 minutes. I think someone (Raven/Beo?) mentioned somewhere they'd done it and posted. I have also. Search for theirs as I wont have time right now to post.

DougM
 
Ok - I'll throw my 0401 story in...

My '97 80 is often used for very short trips by my wife during the school year - :(

Anyhow, early this year we went for a ~200 mile trip after months of short trips. Came home and it threw it's first ever code -> 0401 (as per obd2 code reader). Anyhow, the CEL light went away of it's own accord before I got the code reader on it - but read it out of memory. I reset the code and it hasn't come back yet after 10 months (now I've done it...) - and the bulb ISN'T burnt out. We did several 400 - 1000 mile trips after that (highway+offroad) and all is still running happily.

Makes me think our 80 likes the open road :)

cheers,
george.
 
Bastid......
 
Doug,

My concern is as soon as I install the new VSV I'm gonna start getting CEL again :frown:. In theory it doesn't make sense but as I read posts from the others with new P0401 parts and CEL, it scares me. As I mentioned before that my CEL has been gone for few days now and I don't wanna touch it if it is not coming on again. Removing the VSV is not an issue for me. I have seen B's post before about removing the VSV without removing all the other stuff (Thanks Raven for that link anyway). I would also like to replace all the little hoses under the intake as they are pretty hard now. I also got some hoses from Dan so I am thinking it would be easier (or wise) to take the intake off so I can keep track of all the hoses (i.e. what goes where). I have a tendency of losing track of things :). Anyway, carry on. I really hope you find a concrete solution to this :cheers:.
 
Well, we all knew it would happen, and it did.

After approx 1000 miles the orange light from hell came back on.

I am at a higher altitude than usual ( 1700 vs sea level); wondering
if that is related?

My next stop is the only dealership east of the Mississippi that has competent mechanics; been farting with this long enough.

g
 
Beowulf said:
I yelled "uncle" took it to a trusted Toyota mechanic. He pulled out his Toyota Tester, hooked it up and said "the VSV is bad." Ordered a new one, R&R, and 6 years later it is still working fine. (disclaimer: Results not typical.)

-B-
Click to expand...

B,
What did the dealership charge you for the test?
 
It was done at an indy and that was over 5 years ago. I believe the total bill including the VSV was about $200.
-B-
 
That's what I figured. Now, there are 2 VSV's, aren't there? A VSV for EGR and a VSV for....?


I did replace my VSV for EGR, but I have NOT replaced the hoses, nor have I checked the temp sensor.
 
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