Cleared 0401 without removing throttle body (1 Viewer)

Joined
Apr 24, 2011
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231
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Orange County, CA
After driving with the 0401 light on since I bought it, Its finally cleared!

I know there are a million of these but I thought I should share ;)
For the last four years I' been clearing the code with the scangauge before getting the smog test and it has never been a problem until now. The same place wouldn't pass it this time because the computer wasn't on "ready mode". I don't know why it wasn't a problem before. I doubt the test operator can bypass but I'm not sure.

Some of the tests and procedures in the FSM seemed complicated and required the throttle body and intake to be removed. So, following the many threads on the subject I was able to easily find the problem which was the VSV and replaced it without removing half the engine. Wasn't super easy and my hands got a little scratched but made it!

As per some of the threads the main culprits are the VSV, Modulator, clogged orifices and then gas temp sensor or EGR.

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-First I decided to check the easy access parts and the most talked about is the orifice that goes through the air intake. I was under the impression that it was pretty deep and used a long welding wire. Thought I hit a blockage and pushed it hard (S#@& !), is only about three inches and then you poke a hole through a hose on the underside and when tried to replace it, the hose broke and the tip stayed on the nipple in the hardest most hidden part of the intake under side.:bang:

Anyway, orifice was fine so checked continuity on the gas temp sensor right by the orifice and it checked fine.

-Next was the modulator which was tested by following one of the thread which I couldn't find again but it is a lot easier than FSM. It easily comes out by removing the hoses and you can blow and suck on the bottom nipple to check for suction or resistance of the diaphragm. It checked fine so I cleaned the felt filter by just removing the top cap and checked for air when you blow on the side nipple while covering the two on the opposite side. Air should go through the filter.

-Lastly it was on to the VSV. The FSM asks for removing air intake to check resistance and to blow on one side and for it to come out the other side. Then, by connecting 12 volts directly it should close and air would come out of its filter instead of the opposite side.
One of the threads pointed at the harness sitting on the front side of the throttle body To perform both test without removing it (Thank you MUD). The harness has four wires but the two yellow opposite wires on top go to the VSV and it can be tested without removal (assuming those wires are OK)
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I didn't even have to do the second test. There was no continuity at all.
FSM "Resistance: 37 − 44 Ω at 20°C (68°F) If there is no continuity, replace the VSV."

So because I'm lazy I decided to remove it without removing air intake or throttle body. First removed the modulator and the top bolt of the long intake bracket on the driver side. The bottom bolt was only loosened with a swivel breaker bar and a short extension from under the vehicle.
Then by undoing the one bolt visible from the underside (about 30" of extensions) and the other through the driver side from the top with a gear wrench, the VSV was lose. Easier said than done though. Both where pretty tight so had to find a 6 point socket because the 12 point was damaging the heads and then had to deal with the hoses.

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My hands where a little scratched but after a couple hours including the time consuming mishaps, it was all done. (Putting everything back probably took only 15 min)

Hint. (Bolts are not actually that hard to reach. To make it easier when installing VSV back, I kind of aligned it and used the bolt from underneath with the extensions to push and drive it into it's hole. That made installing the other bolt much easier)

Take into consideration that I'm a :banana: mechanic.


I've gone through the test cycle a couple times and it hasn't come back so far. Scangauge shows all clear and ready :)


On a side note, Napa doesn't carry the right size vacuum hoses even though a friend at the dealer said that they get their hoses there for the used vehicles. Had to order a piece of I believe two feet for about $18 from Toyota :doh:. It is much nicer and heavier duty than what Napa and other auto parts have.
 
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Joined
Mar 25, 2005
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Edmond, Oklahoma
Great writeup. Any pics you can share? Or is there another thread with directions and pics? I just picked up a 97 40th a few weeks back and it also had a 401 showing up.
 

Tedward

95 LC
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Got some pics of this on my phone and will try to get them here. However, I am better at working on the station wagon than sharing pics of it......
 
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Nice work. It is a pain to do either way, but your hands and arms do not get so torn up by taking off upper intake. I understand why do did not though. I opt for less scratches and more work.
 
Joined
Apr 24, 2011
Messages
231
Location
Orange County, CA
I added some pictures to the original post and a little more information.
Also this:
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12mm wrench screwdriver, extensions, swivel breaker bar 12mm and 14mm socket.
Extension mirror, light and curved niddle nose pliers were also used to deal with the hose I broke.
 
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Joined
Apr 27, 2014
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940
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Bozeman
Depending on where you live they may have changed the emissions standards. I found this out where I lived in California that at some point they realized people were just clearing the code or pulling the bulb so now all smog places legally have to check the computer and see if it is throwing a code or not, even if there is no CEL on the dash and that's probably why you failed this time around. Same thing happened to me. The tech that was doing the test told me that the computer had to have been through the complete drive cycle and be in "ready mode" so that they could see if there were any codes. If it wasn't "ready" it was an automatic fail. Good detailed write up and pictures. I'm sure this will help someone down the road.
 
Joined
Apr 24, 2011
Messages
231
Location
Orange County, CA
Depending on where you live they may have changed the emissions standards. I found this out where I lived in California that at some point they realized people were just clearing the code or pulling the bulb so now all smog places legally have to check the computer and see if it is throwing a code or not, even if there is no CEL on the dash and that's probably why you failed this time around. Same thing happened to me. The tech that was doing the test told me that the computer had to have been through the complete drive cycle and be in "ready mode" so that they could see if there were any codes. If it wasn't "ready" it was an automatic fail. Good detailed write up and pictures. I'm sure this will help someone down the road.
I am in California and asked the guy at the smog place if that had changed but he said no. What changed since the last time is the ownership of the shop and the operator.
 
Joined
Apr 27, 2014
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940
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Bozeman
@Alexbv might be different in different counties. I was in the east bay when this happened and we have been taking our cruisers to him for a long time.
 
Joined
Apr 9, 2013
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1,281
I did this job this past weekend, and got it done, but it's pretty tough. If you elect to replace the VSV without removing the upper intake, be prepared for a very tight fit under the intake as you try to get your tools in there to remove the VSV. If you have large or think hands, don't bother. It's very tight in there.

Also, I found it impossible to disconnect the electrical plug on the VSV until I removed both vacuum lines from the VSV, and then carefully pulled the electrical plug and VSV out as much as possible to the DS and got the plug exposed. Then I gingerly got a pair of pliers on the clip and squeezed it, and removed it. I couldn't do it by hand, and it was very difficult and frustrating. I know we have all had difficulties with these Mr. T connectors, and sometimes they break. I just could not get this one off without a tool, and it was tough to get it exposed and at an angle where I could get a tool on it.

The job is done, the code is cleared and all seems fine. However, if I had it to do over again I would just take off the intake. That's my two cents. Total time would have been about the same, and I think the frustration would have been a lot lower.
Also, if you need to do your injectors and/or fuel filter, plan to do them at the same time you do the VSV. It's all right there.

YMMV.
 

cartercd

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Aug 31, 2004
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Chandler, AZ
I just tackled this today - thanks for the write-up, it was very helpful. In addition to replacing all the vacuum lines of the VSV, I also removed the VCV for EVAP and replaced those lines. If you go through the trouble of removing the intake support bracket and the VSV bracket, you might as well do it "while you're in there". The diagram from the FSM below will help you route all the lines.

I found removing the VSV bracket the easy part - getting your hands underneath the intake to connect hoses was the hard part.

I did not order any special metric vacuum lines. Years ago I went to Napa and said "give me 3 feet of every diameter vacuum line you have". I was able to get an acceptable fit on everything.

If you use the Dorman 911-850 VSV you do need to file off a small guide on the electrical connector for it to fit. Speaking of electrical connectors, there is probably a greater than 50% chance you will break the locking mechanism on your old, brittle connector. I am banking on friction to keep mine together.

This is possible even if you have big hands...but those big hands will be full of scratches after you're done.



EGR.JPG
 
Joined
Jan 17, 2017
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381
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PNW, USA
How did this hold up after a few years? Before my VSV arrives, I am trying to decide how to proceed. Without removing the TB, those small vacuum ports seem impossible to clean and I'm also trying to figure out if it's really possible to clean the two intake passages without removing the upper intake. Anyone done this?
 
Joined
Jan 17, 2017
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PNW, USA
Thanks OP and others for this thread with pictures. Wanted to share my slight variation in replacing the VSV a couple days ago. I ran out of good weather to do all the tests but nevertheless, may help someone.

So I actually began by removing the Throttle Body because I wanted to visualize the EGR-to-Intake passage and also make sure that the small TB ports were clear. I got it all disconnected apart from the transmission kickdown cable which allowed me to lift and maneuver it. Now from the passenger side, I could stick my hand in there to disconnect the blue connecter to the VSV. I could also pull off the two vacuum line connections with long needle nose pliers. One from the PS and one from DS without removing the intake bracket. I put my new VSV near the other electrical connections on the TB and routed the new vacuum lines (90999-92003 was cheap and worked great) and zip-tied in place. Putting everything back was a cinch after that and one day I'll externally mount the VSV properly.

My quick test with vacuum pump 3-way'ed in between vacuum modulator and egr valve unfortunately did not show vacuum at 2,500rpm...but the VSV tested right electrically and everything is getting the right voltage. I haven't had a chance to drive much or check TB ports for vacuum but all in all the hardest part was simply reaching into the middle of the engine bay to do all this.


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