9 times out of 10 a PO401 Code is fixed by . . . . . (1 Viewer)

[Grench]

That 'port' goes through the intake and not into it. There is another vacuum hose attached to the opposite side (underside) of the intake. If you are not careful when clearing that port, you can push that lower hose off or tear right through it.

Brings up another thing that can throw the code...

Check the little hose on the barb on the DS of the intake to make sure its still connected and not cracked/rotted.

IMHO the fact that this port runs through the intake is one of the great mysteries of Toyota design. It had to be expensive to put the ports on and run the line through the intake instead of just running a vac hose or even a SS hard line over the top of it. So, they were trying to accomplish something... but what/why?

 

[LandCrusher'70]

IMHO the fact that this port runs through the intake is one of the great mysteries of Toyota design. It had to be expensive to put the ports on and run the line through the intake instead of just running a vac hose or even a SS hard line over the top of it. So, they were trying to accomplish something... but what/why?

And to continue down the line; The 'port' is connected via a vacuum line to a hardline that is bent around the VSV for EGR and uses another small vac line to make the final connection.

 

[Grench]

And to continue down the line; The 'port' is connected via a vacuum line to a hardline that is bent around the VSV for EGR and uses another small vac line to make the final connection.

And don't forget that the destination of all of this is another valve under the intake who's purpose is to -defeat- the vacuum.

Rube Goldberg - Wikipedia, the free encyclopedia

 

[Voivod]

It had to be expensive to put the ports on and run the line through the intake instead of just running a vac hose or even a SS hard line over the top of it. So, they were trying to accomplish something... but what/why?

Kaizen!

(that failed)

 

[jlg32281]

I hope it's the vsv, i'm going all in on that. i'll be buying one soon.

 

[superjuice]

I went ahead and just replaced the VSV, no code in six months. When i checked the one i took out it passed all tests, i hear once it heats up it starts to fail. Did it with the intake in place, not fun, but definatly doable...good luck

 

[NLXTACY]

...or get a drill bit stuck in it like Joey!

bastard!

I was reading that thinking to myself, "yup someone is going to point out I was an idiot". Sure enough.

If you want to laugh:
https://forum.ih8mud.com/80-series-tech/226972-while-trying-rid-p0401-cel-i-learned-i-am-dumb.html

 

[NLXTACY]

BTW, my P0401 was a stupid cracked vacuum hose. It just came back two weeks ago so I will be replacing ALL the vacuum hoses first.

 

[d0ubledown]

i too wonder as to why toyota decided to put the vsv under the intake manifold, and have vacuum run through the plenums. i ought to change my vsv for egr as its been about a year of the lovely orange check engine light staring at me. is there point to resetting it even if it will just come back? or does it not make a difference to clear the code?

for those that actually followed the fsm to remove the vsv by taking off the upper intake, was it a difficult job to remove the upper plenum? a 2 or 3 ? what other parts are needed? im guessing intake gaskets? tb gasket? did you get at all the nuts & bolts for the intake from the hood or under the wheel well?

 

[SeanAndHis80]

i too wonder as to why toyota decided to put the vsv under the intake manifold, and have vacuum run through the plenums. i ought to change my vsv for egr as its been about a year of the lovely orange check engine light staring at me. is there point to resetting it even if it will just come back? or does it not make a difference to clear the code?

for those that actually followed the fsm to remove the vsv by taking off the upper intake, was it a difficult job to remove the upper plenum? a 2 or 3 ? what other parts are needed? im guessing intake gaskets? tb gasket? did you get at all the nuts & bolts for the intake from the hood or under the wheel well?

gaskets as mentioned, genuine Toyota vacuum hose - I think I got 3 feet. Most bolts accessed from under the truck/engine. I did it in an afternoon. I think it is the best way to do the VSV as you can easily see & replace all the hoses under there.

 

[edog's 80]

gaskets as mentioned, genuine Toyota vacuum hose - I think I got 3 feet. Most bolts accessed from under the truck/engine. I did it in an afternoon. I think it is the best way to do the VSV as you can easily see & replace all the hoses under there.

I did the same thing. I too agree that this is the proper way to get at the VSV for EGR, it's not that difficult to get the upper intake off.

You should get a TB gasket, about 3 ft of vacuum hose, and the intake gaskets. I did my fuel filter while I was in there. If you have time, your injectors are also exposed if you want to send them in or take them in somewhere to get cleaned. Lot's of brake cleaner is good too so you can clean the TB and the upper intake.

You will need lots of extensions to get at the lower bolts, it gets tiresome because all of your work is overhead and upside down, but it's not too difficult. When your upper intake is off grab some clean shop towels and stuff them in the exposed intake holes so you don't drop a bolt or nut or whatever else in there. I don't know if you could get anything out of there if you happened to drop something in there.

 

[LandCrusher'70]

for those that actually followed the fsm to remove the vsv by taking off the upper intake, was it a difficult job to remove the upper plenum? a 2 or 3 ? what other parts are needed? im guessing intake gaskets? tb gasket? did you get at all the nuts & bolts for the intake from the hood or under the wheel well?

DO NOT take the intake apart, unless you're in there to do other work (i.e.: cleaning the intake). It's way more work than is necessary. You can get the VSV for EGR out and tested within 15 minutes and you don't need to buy/replace gaskets.

 

[SeanAndHis80]

DO NOT take the intake apart, unless you're in there to do other work (i.e.: cleaning the intake). It's way more work than is necessary. You can get the VSV for EGR out and tested within 15 minutes and you don't need to buy/replace gaskets.

But what is the condition of the rubber hoses under the plenum? Mine were hard and cracked. IMO this is bad advice - if you are going to spend the time to fix it why not fix it right. Also, there is no need to take the VSV out to test it.

 

[aktundra]

Well the weekend trip that started this whole post is done, 8 hrs of driving 60-80 mph pushing a bunch of air with an RTT, crawling through road construction, over mt. passes, round motor homes on a 2-lane, ect ect (and a very little beach wheeling !).

Super trip, did not trip a po401 code.

However the scan gauge was readin IA at 15-25 degrees above the ambient temp. Perhaps unrelated, but it seemed to me that IA was usually just a few degrees over ambient air temp.

For those that understand this system, does this seem unusual or lend a clue to the diagnosis ?

Well-none-the-less, thanks for the comments. looks like I willl have time to chase this down.

 

[LandCrusher'70]

But what is the condition of the rubber hoses under the plenum? Mine were hard and cracked. IMO this is bad advice - if you are going to spend the time to fix it why not fix it right.

Who cares what the condition is? Just replace all of the vacuum lines. Why wouldn't you? They're cheap and they're all accessible without removing the intake! I've got fresh rubber throughout.

Also, there is no need to take the VSV out to test it.

Haha, but there is a need to remove the upper intake!?



Remove 4 bolts / loosen 1. That's all it takes to check your EGR bits.

 

[Pskhaat]

... replaced the plugs with cooler MR2 turbo ones

What did this buy you?

 

[Grench]

What did this buy you?

The ones that Cruiserdan suggested I buy when I was ordering the Supercharger and all of the bits & pieces to freshen up under the hood. I'm certain he could rattle off the part number without looking it up.

Edit: The idea is to run a bit cooler plug to help prevent knock.

 

[Pskhaat]

Do you think it makes sense to run them for us who are in extreme summer heat for the same reason?

 

[d0ubledown]

I did the same thing. I too agree that this is the proper way to get at the VSV for EGR, it's not that difficult to get the upper intake off.

You should get a TB gasket, about 3 ft of vacuum hose, and the intake gaskets. I did my fuel filter while I was in there. If you have time, your injectors are also exposed if you want to send them in or take them in somewhere to get cleaned. Lot's of brake cleaner is good too so you can clean the TB and the upper intake.

You will need lots of extensions to get at the lower bolts, it gets tiresome because all of your work is overhead and upside down, but it's not too difficult. When your upper intake is off grab some clean shop towels and stuff them in the exposed intake holes so you don't drop a bolt or nut or whatever else in there. I don't know if you could get anything out of there if you happened to drop something in there.

thanks for the heads up. ill probably end up pulling the intake off, since i also have a new fuel filter thats been sitting for a year waiting to go in. access to the vsv hoses as well...and i'll do a thorough cleaning of the TB and intake plenums. i hate having scratched up hands trying to shoehorn them into tight places...doing the PHH was bad enough.

does toyota sell the proper vacuum hose per foot? i recall reading the size was an oddball one. anyone know the prope size ID/OD of the vacuum lines? will probably get some from the parts store instead of the stealership...

 

[Grench]

Do you think it makes sense to run them for us who are in extreme summer heat for the same reason?

Sorry. I have no idea. Talk to Dan or see if anyone else here catches on it.