P401 - EGR - 2.7l 3RZ - Help

I have a P401 error code.

I have:
replaced the VSV valve twice (both used, wanted to make sure)
cleaned and replaced the EGR
cleaned the temp sensor
cleaned the throttle body
inspected all hoses and connectes
inspected and cleaned the exhaust gas return pipe

Any thoughts?

 

What about the vacuum modulator? Did you actually check that none of the hoses/pipes are clogged? (Not sure what you meant by "inspect".) And you can check the resistance of the VSV, and also apply power and see if it lets air through and no air when there's no power applied. (See the repair manual, VSV for EGR, VSV Inspection.)

 

Dumb question, but have you cleared the 401 code, to see if it returns?

 

before all this happened, did you by any chance clean your throttle body or remove the vacuum lines from it? if not then they cant be connected in the wrong order (very common mistake made) so instead look around and check for broken vacuum lines.

 

The check engine for P401 has been on for about 100k miles.. previous owner did nothing and I was focusing on fixing other things. (Truck has 410K)

The vaccum modulator has been replaced, but I have not tested teh VSV with power. I also need to check how to test the resistance of the VSV. By inspect I meant take disconnect the hoses and make sure they are not clogged. The throttle body has also been cleaned.

I have reset the code multiple times, it wills stay for for 2-4 days anywhere between 50 and 250 miles.

Im getting to the point if I can find a 2rz or 3rz with all EGR components, just replace all the things.

 

By this, do you mean the main EGR valve?
BTW, there is an easy test for the main valve.

There are 2 tests:
Having a smooth idle means that it closes all the way, as it should.
Sucking on the vacuum line to that valve should cause a stall.

 

So if it stalls when you suck on the vacuum line to the EGR it should be good? Because I'm kind of trying to troubleshoot a rough idle.

 

if unplugging and sucking on the vacuum line to the EGR gets a difference in idle, then the EGR is working ok and you need to determine if the EGR might just have a bad temp sensor throwing the code for no reason. right behind the TPS there is a small little plug that screws into the intake to sense the EGR heat as the gas enters the intake manifold, if its bad it throws an insufficient EGR flow code because it isn't working. I would replace this sensor first before going into major parts replacements.

now when I cleaned my throttle body I put the 3 small vacuum lines on top of the TB on wrong and it was throwing the p401 code because the EGR wasn't getting the correct vacuum. since this has been going on since you got it, the previous owner may have gotten these hoses mixed up so set them in the correct position based on this video to be sure they are correct. they should all lay in order from right to left and not cross over each other.

https://www.youtube.com/watch?v=zKVdlT93j0o


this is how it the EGR temp sensor works:

https://www.youtube.com/watch?v=Oqh-xa2UitM

 

^ So if there is no difference in idle when I disconnect my EGR and plug the lines vs reconnected then my EGR is bad?

 

if sucking on the vacuum line connected to the EGR, it should make it open and let exhaust gas into the intake changing how it idles so if nothing happens when you do that then yes it is bad or the EGR tube from exhaust or into TB is plugged up not letting the exhaust gas flow when the EGR opens.

 

Oh ok, yea it stalls when I suck on the vac line off the EGR. But when I just plug/disconnect the vac line from the EGR nothing happens.

Thanks

 

that's because it only gets vacuum to open the EGR when its at cruising speeds, but when you are at idle or full throttle it stays closed, or its supposed to if its working correctly.

 

I also have this problem and did the same : Replaced/checked everything with no cure
A search on here shows the same results, I suppose no one has found the cure ?

 

The Toyota Factory Service manual (FSM) recomends every check I just went through
but in a search here, an ASE master mechanic posted a long time ago that the ECU anticipates a signal change from the front 02 sensor (AF sensor) when it gets the signal from the EGR temperature sensor that EGR is on, and so a dirty AF sensor will cause a PO401
Which makes some sense, because I will not get any "codes pending" until I am at 50 mph, where the EGR temp sensor would send the signal to tell the VSV to close EGR , (not the around town vacuum modulator control)
Correct me if I am wrong

I heard a long time ago that often times the reason for a code will sometimes be totally unrelated to the system indicated, or related sensors of the system that is being indicated by the code number shown

I guess I will roll the dice and throw a AF sensor at this

 

I had a very similar issue with my 95.5 2rz.. I’d clear the codes run good for a little, and code would come back and truck would run like crap. After changing out the Egr valve and sensor, trying wires to make sure there were no shorts, problem still occurred. Led me to think a capacitor in the ECU was burnt out causing the code. Sure enough, I found a local shop in my area to bench test my ECU, and boom! Had my ECU rebuilt and haven’t had an issue since. Hope this helps.

 

I did not read all the posts but you might want to check your PCV valve. Also make sure it’s not stuck open. Make sure the hose good and it’s not leaking, also make sure you check your little exhaust tube from the EGR valve and connect just below the exhaust manifold. Make sure it’s not leaking or compromised or gunked. Make sure you got a good seal on your gasket or you attached the EGR and your vacuum modulator has a clean filter in it working properly no hoses crimped. Also make sure you’re not buying the cheap aftermarket parts or the Chinese counterfeits and knock offs from eBay and Amazon many many many times these parts are garbage and do not function, or they’re just flat out counterfeits with Denzo and Bosch written on the side of them, but totally counterfeit (never buy anything from an online vendor from China) you probably already know that, but just a though, make sure you’re using quality parts. if t
You replaced an EGR valve that came from one of those Chinese vendors on Amazon and eBay that could be the issue. Or any other parts or not OEM high-quality just throwing stuff out there ,brainstorming, and I’m sure you’re probably already know that. Make sure you make sure your vacuum houses are pulling pressure and you don’t have a vacuum issue that’s not enough pressure to open EGR valve. Check the coolant system make sure you get in good flow through the coolent hose that runs beneath the vacuum canister on the EGR valve