P0401 Defeated - with pics (1 Viewer)
- Thread starter Flank
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Just adding a data point to the collective knowledge.
This pic is of my failed EGR modulator. Notice the small dark stain on the filter element. It lines up with the hole to the diaphragm. I am fairly certain that it was created by exhaust gas passing the diaphragm and exiting the filter.
Even without testing to see if the unit holds vacuum, I suspect you won't go wrong replacing the modulator if you see a similar stain on the filter.
This pic is of my failed EGR modulator. Notice the small dark stain on the filter element. It lines up with the hole to the diaphragm. I am fairly certain that it was created by exhaust gas passing the diaphragm and exiting the filter.
Even without testing to see if the unit holds vacuum, I suspect you won't go wrong replacing the modulator if you see a similar stain on the filter.
First, thanks to all the excellent information on this thread! For my '97 LX450 I've done my best to follow all the advice (disassembling and cleaning the upper intake manifold, etc.) and am down to checking individual components. In the FSM, when checking the EGR valve one step is to put a T splice into the hose from the EGR valve to the EGR modulator to connect a vacuum gauge, and then take the hose from "Port R" on the modulator and feed it into the intake manifold. The FSM says that under these conditions, a hot engine, and 2500 RPM, one should see "high vacuum" on the gauge. Under these conditions my gauge says 6.5 in. Hg vacuum and what I would like to know is if that is "high vacuum", or if not do I have a problem with the EGR modulator or valve. Many thanks in advance!
NorCalDoug
problems solved daily...
nice!
There is a thread here somewhere that had a much easier procedure to follow than the FSM using a MityVac. I followed it to find that my Modulator was bad and my EGR was good. I replaced the mod and still had the code. I then went after the VSV and swapped out all the vacuum lines while I was in there. No more code. I believe the diaphragm on the mod fails and then allows the system to ingest exhaust gas that slowly clogs up all the small tubes. The tube through the intake manifold was completely plugged.
Here is the procedure I followed,
You have to figure out which component within the system is causing your issue. I would first make sure that port going from the EGR valve through to the top of the intake is clear. That is a known culprit that doesn't require parts to fix. From there, you just have to follow the troubleshooting to find your problem(s). On a rare occasion it's multiple things. Top offenders include that port, the VSV (under the intake), and the vacuum modulator. Good vacuum lines are helpful too. Less frequently folks have mentioned the temp sensor, or on rare occasion the EGR valve itself.
Why do you need to fix it so fast anyway? Clear the code again and wait for the right time to fix - that is what I did for three years. To answer your question I think VSV edges out the diaphragm which edges out the rubber tubing, which edges out a clogged throttle body passage, which edges out the EGR valve, which edges out the EGR temp sensor. Nothing definitive and a likely waste of $$$ if you throw parts at it.
I had a hard fault in mine (just "fixed" it a few weeks ago actually) that is, clear the code, and within 3 miles the light would pop on again. All I did was:
Take off the VSV, tested it and confirmed that it functioned properly (easy to access when the throttle body is taken off, which is pretty easy to remove as well)
Checked all vacuum lines and replaced some that seemed loose/might not be sealing.
Checked the EGR vacuum modulator.
Checked EGR valve diaphragm
Installed the vacuum gauge and drove it around and BAM...no more MIL. So in my case, what I "fixed" is unclear. But it really is a pretty easy thing to repair. You sound a little intimidated, don't be...read the threads and fix it when you have the time.
When I got my PO401, I replaced the vacuum modulator valve with the new type ($65)...nope. I replaced the VSV for EGR ($73)...nope. Took apart the EGR valve, cleaned and re-installed...nope. Finally, (and I tell this story just to suggest reversing the order of troubleshooting per super90) I cleaned the little vacuum port that goes into the intake with a piece of stiff wire. I thought it went into the intake, but it actually goes THRU the intake, so use a long piece of wire, and disconnect the hose connected to the other end of the port under/inside the intake (sort of hard to access) before you start cleaning. I cracked the flux off a piece of 7018 welding rod and used it to clean with, because it is stiff and straight. I used a drill bit first, before I realized how long the vacuum port tube was. For me, this was the fix. Have not had a PO401 in the 2 years since. If I had tried this first, I would have fixed it for free. Instead, I have a nice supply of back-up parts should either of them fail (for $138 )
Step 1: remove all of the EGR crap
Step 2: make some block off plates
Step 3: Install the radio shack resistor. Don't remember 4.7K something (off memory).
Step 4: clear code and enjoy driving with no CEL for EGR Crap.
even if you have emissions, I doubt the tech is going to know it is missing and I "think" it pass's the sniffer as well.
I did it on the wife's 96 about 2000 miles ago with NO issues.
Make sure that tiny little hose between the front TPS (throttle position) and the other sensor is hooked up. ( The two sensors on the front of the intake.)
There is a tiny hose below , and right between the TPS and the other sensor.
My code kept going off until I hooked it back up. It's small, and difficult to see without a flashlight. And I couldn't attach it without angled pliers.
It's very easy to overlook after you've hooked everything back up after a throttle cleaning, EGR fixes.
Po401 fixed with relay and resistors.
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Thank you for this!
Hey Guys... fighting the good fight against the 401 code... looking all over but, could not find where this port actually is... any help with pics?
I threw a P0401 code last week. After reading through these threads, I just had the shop knock mine out. Parts and labor came to $521.41, and they replaced the EGR solenoid, Vacuum valve, and cleaned the ports. Just food for thought for those weighing doing this repair yourself, or taking it to a shop.
thanks a ton! Ok, so I am not wasting work... I would first take off the throttle body (which I am sure could use a cleaning) and then clean out that port. sound right?
Thanks Flank. Ordered up the whole pot of parts (vsv, modulator, intake gasket, tb gasket... plus some other stuff). Gonna start with the modulator (saw that post with the black dot on the filter...). Then going to pull the TB, clean it, inspect and clear up that passage.
Thanks again!
Is there a write up on this? Will this work if I delete my egr system?
Hate to as an obvious (to most) question, but how do I go about doing this?
Should've posted awhile ago, but I had a recurring P0401 a year or so ago. I did basically everything done by the OP while I did my supercharger install. My intake planum port was pretty well blocked with carbon. Anyway, it worked great. Haven't had a P0401 since.
@4G63 POWER and @LX450inNash Here are some links I saved for myself about EGR delete, hope this helps you guys out. I really want to do this mod as well but its to damn cold out for me to tackle doing this in my driveway! I'll get around to it someday though, I hope!
'94 Code 71, EGR Bypass and redneck technique..
Disable the EGR system the (mostly) Toyota way
EGR Readiness Achieved with EGR Removed!
'94 Code 71, EGR Bypass and redneck technique..
Disable the EGR system the (mostly) Toyota way
EGR Readiness Achieved with EGR Removed!
Over the weekend I attempted to tackle my P0401 on my 97 LX450 with 285k, as my inspection/registration is about to expire. I'd replaced the EGR vacuum modulator a couple weeks ago because it didn't pass the test, but that didn't stop P0401 from coming back. I ordered all the gaskets, EGR VSV, some 5/32 and 5/16 vac hose, and dove in.
Removed TB and cleaned, removed upper intake and cleaned out the port (didn't seem to be clogged), replaced EGR VSV and all the little hoses underneath the intake. I left the EGR valve in place because I couldn't get a good grip/leverage on the large nut so I removed the studs and was able to get the upper intake off that way. Put everything back together with new gaskets and hoses where I could.
Started the truck up and was relieved that everything felt and drove the same as before. This was my biggest undertaking on the LX so far and it took me about 8 hours total over Saturday and Sunday. Needless to say, my wife was not happy with me spending that much time on the LX.
Today on my way to lunch P0401 came back
... I don't want to take the truck to the shop, but at this point I doubt I can convince my wife to let me spend any more time fighting P0401.
Any ideas/suggestions before I throw in the towel?
Removed TB and cleaned, removed upper intake and cleaned out the port (didn't seem to be clogged), replaced EGR VSV and all the little hoses underneath the intake. I left the EGR valve in place because I couldn't get a good grip/leverage on the large nut so I removed the studs and was able to get the upper intake off that way. Put everything back together with new gaskets and hoses where I could.
Started the truck up and was relieved that everything felt and drove the same as before. This was my biggest undertaking on the LX so far and it took me about 8 hours total over Saturday and Sunday. Needless to say, my wife was not happy with me spending that much time on the LX.
Today on my way to lunch P0401 came back
... I don't want to take the truck to the shop, but at this point I doubt I can convince my wife to let me spend any more time fighting P0401. Any ideas/suggestions before I throw in the towel?
Some have had good luck with the method documented in the thread linked above
You can read the whole thread or start at about post 33.
