Checking VSV for EGR easy way P0401 (2 Viewers)

[OmanFZJ80]

Hi guys,
I'm here in Oman with hesitation on acceleration that could be from the VSV. Unfortunately I haven't been able to find anybody who can run the computer for codes. Anyway, I checked continuity of the VSV using the method described here. It all tests fine and quietly clicks when connected to 12V. However, what kind of flow should be getting through this thing?

It blows through without power connected, but it isn't free like a straw. There is some resistance. Normal?

I'm trying to chase down hesitation on acceleration up until 2500 RPM with it's like a turbo kicks in and I get full power. VSV on my FZJ80 connects to the fuel pressure regulator only as this GCC spec model didn't come with EGR.
Thanks.

 

[Visuals1134]

Well I got bit with that bug too. Sorry if I missed something, although most common culprit has been long identified - VSV, most of ways to check its operation are rather tedious. Here is my easy way.
Disconnect VSV connector from main engine harness. Check for continuity between two terminals with yellow wires on opposite side. You must have something like 30-35 oms. No continuity = bad VSV.

Otherwise rig up something to connect those terminals to battery.

Then disconnect a vac hose from EGR valve. If you can blow air through or suck it out of it when terminals are connected to battery = bad VSV. (when disconnected - air should be able to flow).

Ones VSV is removed you might want to double check findings but I really fail to see why Toyota in shop manual recommends to remove intake plenum to just check VSV.
If all checks out, look elsewhere.
On the side note. I've seen a advice to clean passage through intake manifold. Well, clogged up passage could only conceivably cause code P0402 not P0401 since it would induce too much vacuum above membrane of EGR valve thus opening it too much. Role of VSV is to prevent vacuum built up unless ECU decides that now is a good time to close it.
Just my $0.02

 

[Visuals1134]

Ah man .so much useful information guys.I am in the middle of tackling down this code after having it come up after I bought my 96 landcruiser and drove away last year.I did the first test to check and see if I had any continuity and it read 34 oms.so next I decided to clean out the modulator and boy was it caked up.I removed the filter and used my air compressor to clean the filter.then I got carried away with the air compressor and proceeded to shoot air through the tiny valves .I flipped the modulator and shot air through the bottom of it and heard a loud pop .now it's in 2 pieces.well guess I'll wait for Amazon to deliver new modulator!doh!

 

[enox]

I know this thread is really old, but...I'm dealing with the 0401 code and I noticed that the vacuum port on the back of the intake manifold (the one that the EGR goes to) I used a small piece of wire to see if it was clogged, wire kept going in then I could see it come out under the manifold...I got on my back and couldn't see up there to find out where it came out of..does anyone know what's under that section or perhaps have a picture showing the underside of the upper intake?

 

[enox]

Ah man .so much useful information guys.I am in the middle of tackling down this code after having it come up after I bought my 96 landcruiser and drove away last year.I did the first test to check and see if I had any continuity and it read 34 oms.so next I decided to clean out the modulator and boy was it caked up.I removed the filter and used my air compressor to clean the filter.then I got carried away with the air compressor and proceeded to shoot air through the tiny valves .I flipped the modulator and shot air through the bottom of it and heard a loud pop .now it's in 2 pieces.well guess I'll wait for Amazon to deliver new modulator!doh!

I too got 33ohms, replaced the modulator, haven't driven yet but I did the test on the vcv with the 12v and couldn't hear anything..is the switching audible?

 

[katalytic]

I know this thread is really old, but...I'm dealing with the 0401 code and I noticed that the vacuum port on the back of the intake manifold (the one that the EGR goes to) I used a small piece of wire to see if it was clogged, wire kept going in then I could see it come out under the manifold...I got on my back and couldn't see up there to find out where it came out of..does anyone know what's under that section or perhaps have a picture showing the underside of the upper intake?

I'll try to resurrect the images that exist on the board. But the fast answer is that at on the other side of the pipe that goes through the intake plenum is a small vacuum hose (90999-9200x - depending on the length you want -- here it's about 4") that plugs into the VSV for EGR part 90910 12079. if the VSV/EGR isn't connected or is bad (highly likely) that could be your problem source.
The bible for me was a post by cahill: "PO401 and EGR/air intake manifold with pictures" . Also super valuable were sbman:"Identify this hose" for a good under manifold shot and Flank:"P0401 defeated - with pics". I can't search and link on the tool I'm using right now but this might give you a start.
Update: Here's Cahill's post that got me moving forward: PO401 and EGR/air intake manifold with pictures
sbman: Identify this hose? and Flank: P0401 Defeated - with pics

I did the plenum removal and rehab, injector cleaning, and valve cover gasket replacement (with all the related hoses and suspect device replacements) project a few months ago and these were the gems that got me through.

Happy hunting!

 

[enox]

I'll try to resurrect the images that exist on the board. But the fast answer is that at on the other side of the pipe that goes through the intake plenum is a small vacuum hose (90999-9200x - depending on the length you want -- here it's about 4") that plugs into the VSV for EGR part 90910 12079. if the VSV/EGR isn't connected or is bad (highly likely) that could be your problem source.
The bible for me was a post by cahill: "PO401 and EGR/air intake manifold with pictures" . Also super valuable were sbman:"Identify this hose" for a good under manifold shot and Flank:"P0401 defeated - with pics". I can't search and link on the tool I'm using right now but this might give you a start. Happy hunting!

thanks! so is that a safe call to disconnect and bypass all together? the tube that goes through the plenum is sealed ? basically I should be able to ditch that hose and run my own from EGR to vsv without the plenum? thanks for your response!

 

[katalytic]

thanks! so is that a safe call to disconnect and bypass all together? the tube that goes through the plenum is sealed ? basically I should be able to ditch that hose and run my own from EGR to vsv without the plenum? thanks for your response!

Right, one of the solutions is to run directly from EGR to VSV with a longer piece of vacuum hose. [The tube going through the plenum is not open to the inside of the plenum, it's just a small metallic straw that clogs easily. ] Those two points must be connected but nothing happens in the plenum, it's just a passthrough. And an annoying one. Just to be clear (ha!), up top, the hose we're talking about starts at the EGR Vacuum Modulator, T's at the EGR and then connects to the plenum tube which goes straight through and hits the VSV/EGR. You can go directly from the EGR tee to the VSV without a functional problem. In fact section EC-2 (page 615 on mine) of the factory shop manual shows routing that looks exactly like that.

 

[fz1boxer]

the pass through on mine was completely plugged also as well as the vacuum post ar the base of the EGR

 

[enox]

Okay cool, I bypassed the tube on the intake plenum. Rerouted. Now I was looking at the vsv and it looks like it has (3) vacuum lines. One is rerouted straight to EGR T, the other goes to a T on a check valve and the third looks like it loops back up to a hard line on the plenum (right by the plenum support) Now looking at vsv's online they appear to only have (2) ports as well as the diagram on my hood. I was looking at replacing with the dorman vsv and it also has (2) vacuum ports. Am I missing something or basically I'm trying to figure out what that third line does...

 

[enox]

Okay cool, I bypassed the tube on the intake plenum. Rerouted. Now I was looking at the vsv and it looks like it has (3) vacuum lines. One is rerouted straight to EGR T, the other goes to a T on a check valve and the third looks like it loops back up to a hard line on the plenum (right by the plenum support) Now looking at vsv's online they appear to only have (2) ports as well as the diagram on my hood. I was looking at replacing with the dorman vsv and it also has (2) vacuum ports. Am I missing something or basically I'm trying to figure out what that third line does...

I was missing something...it doesn't have (3) vacuum lines. one I was looking at goes back into the plenum.

anyways after replacing vacuum modulator, associated upper vacuum lines, bypassing intake tube port. I did have CEL come back on with 0401 and now have removed and cleaned TB last night. haven't driven enough to get light to come back on, however my idle is better.

My P0401 light comes on it seems after big elevation changes, long drives and I usually have to go a minimum of 100mi before it will come back after clearing. Last weekend put about 800mi on and cleared the light 3 times.

as you all know...super annoying. one day. one dam day.

 

[jatree]

Just did this test and got 60 Ohms - anyone seen similar?

 

[Euriq]

Well I got bit with that bug too. Sorry if I missed something, although most common culprit has been long identified - VSV, most of ways to check its operation are rather tedious. Here is my easy way.
Disconnect VSV connector from main engine harness. Check for continuity between two terminals with yellow wires on opposite side. You must have something like 30-35 oms. No continuity = bad VSV.

Otherwise rig up something to connect those terminals to battery.

Then disconnect a vac hose from EGR valve. If you can blow air through or suck it out of it when terminals are connected to battery = bad VSV. (when disconnected - air should be able to flow).

Ones VSV is removed you might want to double check findings but I really fail to see why Toyota in shop manual recommends to remove intake plenum to just check VSV.
If all checks out, look elsewhere.
On the side note. I've seen a advice to clean passage through intake manifold. Well, clogged up passage could only conceivably cause code P0402 not P0401 since it would induce too much vacuum above membrane of EGR valve thus opening it too much. Role of VSV is to prevent vacuum built up unless ECU decides that now is a good time to close it.
Just my $0.02

Awesome post it’s been super helpful! I just attempted to connect the battery to the VSV and before testing I tried to blow through the hose going from the VSV to the EGR valve. I found that I can’t blow any air through the EGR valve. Is it safe to assume that the valve has failed in a closed position and there is my problem?