Alternate EGR tests ( P0401 ) (1 Viewer)

[RavenTai]

RavinTai I just saw your post and see that you work in the same area. I work in Toc 3 Bay 11. You can leave yet this 401 code is getting the best of me and I have to pass emissions test in a month.

More of us? 260 or 410? was it you that used to park out in the east lot outside 12 on day shift? I used to see an silver 80 sitting there when I came in, I think it was a 40th, parked by it a couple times in my black LX450, there is another one that parks down by stores,

Get the factory manuals and start with the FSM tests, then move on to what I outline above, it will find the problem.


I am in FL right now will be back in Dec if you need a hand with it,

 

[scoop]

Yes thats was my 40th. I remember your LX450. I am in 411 A/C Paint. I just got home with the Vac gauge and am printing out your post. Wish me luck.

 

[RavenTai]

Good luck, let us know what you come up with.

 

[scoop]

I hooked up the Mityvac to the egr. Plugged one side as you described. It does not hold any vac. I am going to replace it next. Thanks,

 

[scoop]

401 Still Alive and Well

EGR Valve (Replaced with OEM)

EGR Modulator (Replaced with OEM)

Vacuum Lines (Replaced most and checked all)

VSV valve (2 years old) I removed it and checked ok per FSM. Heated with a heat gun and still checked ok.

TVV valve I did all FSM checks and it checks ok.

Check valve (Orange and black) above TVV remove and checked ok.

I did the driving test with the vacuum gauge and my reading were the same as described. I have not done a cold test yet but am planning to tommorrow morning.

The only thing I have not checked is the EGR temp sensor. I guess I will give that a try also in the morning.

I would like to here anyones ideas on this. I am almost stuck.

Thanks,

 

[Beowulf]

Vacuum port that goes through the intake. Clean the EGR temp sensor and test it per the FSM. (This is rarely the problem though).

Carefully check all vacuum hoses again if the port through the intake is clear.

-B-

 

[NLXTACY]

Did you check for drill bits

Sorry inside joke, had to be there

 

[Chris Wilcox]

You do sound almost stuck. hmmm. I obviously don't know your whole situation however my assumption would be that if the vacuum signal is showing as working properly then there is nothing on that side I can think of that is incorrect. You should be sending exhaust gas to the temp sensor when expected by the computer and that should be enough to satisfy it. Check the sensor and maybe the wiring to the ECU. You will find it. Some have fooled the system by installing a resistor or something. That would confirm function of that side of the system. Just throwing out ideas.
Chris

 

[scoop]

Yes I had the resistor hooked up for a few months. That stopped the code and tells me the wiring is ok but it want pass emmissions test with a resistor installed.

Going to check vacuum port that goes through the intake and Temp sensor.

 

[Chris Wilcox]

You're doing what I would do in checking the temp sensor. My FSM (1997) is on page SF-62
50C 64-97 kohm
100C 11-16 kohm
150C 2-4 kohm

If I remember correctly, the vacuum line through the intake manifold goes from EGR valve to the VSV. Since the VSV just Veto's vacuum signal to the EGR valve, you should be looking for leaks and not plugs in that line. A leak would veto signal all the time whereas a plug would be the same as removing the line and hooknig vacuum gauge directly as per Raven
"To test with is witch the other way is to watch just the modulator alone: remove the short line that runs from the nipple on the intake manifold and goes to the EGR valve, plug the intake nipple and hook the sense line from the cab to the EGR valve, (see pic 2)"

One more document I referenced.
http://www.autoshop101.com/forms/h61.pdf

Chris

 

[scoop]

The Temp Sensor checked ok and vacuum lines to it are ok.

I put a tee in the vacuum line between egr and modulator. With the engine cold I had no vacuum. I unhooked the line betwen TVV and canister. No vacuum @ 2500 rpm. I drove while watching vacuum gauge and as soon as engine warmed up I got the correct readings. I had 0 vacuum until warm up. I pulled the line to the TVV and @ 2500 rpm I had vacuum with engine warm.

I am officially stuck.

I am going to drive arond and make sure it is still kicking 401 code I may have bumped into something and fixed it..

200.00 Bucks and 22 man hours so far.

 

[scoop]

Must have bumped into something. Drove it until scan gauge said OBD was ready and no code. Pulled in and got emmissions test done. It passed 30 miles and no CEL. If it comes back now I will just put the resistor back and wait till next year.

 

[Chris Wilcox]

good to hear, now if it will only stay this way.
Chris

 

[Cube Dweller]

Raven, another awesome writeup, thanks for condensing the FSM into easy to follow steps for troubleshooting

I followed your test routine. After the initial warm up phase, I started pulling 5-8 inches of Hg under normal throttle. Once the truck warmed up, the vacuum dropped to zero. I pinched the line from the intake to the egr, vacuum came back and within 25 feet of driving the CEL clicked off. I'm gonna call CDan tomorrow.

 

[RavenTai]

sounds like another "VSV bad when warm"

Glad you found the problem

 

[super90]

Fellas, don't forget to make sure that the port that flows from the EGR valve into the top of the intake is not plugged. It throws a Code 71 (OBDI system on my '94). Mine was plugged a few years ago and was a devil to figure out. All the FSM test for all the EGR components passed and I was stumped as was my local indy at the time. I finally just took apart the whole system and pulled the top of the manifold to do lots of other PM and found the plugged port.

Local mechanic here in Dallas that worked at the Lexus dealership for a long time said that port gets plugged plenty often and was one of the first places they would look on the LX450s. A cheap and easy fix requiring no parts.

Happy to see that the troubleshooting of this problem has advanced so much. When I had the problem, it wasn't so well sorted out.

Keep the Cruiser Faith !

R.

 

[edog's 80]

Fellas, don't forget to make sure that the port that flows from the EGR valve into the top of the intake is not plugged. It throws a Code 71 (OBDI system on my '94). Mine was plugged a few years ago and was a devil to figure out. All the FSM test for all the EGR components passed and I was stumped as was my local indy at the time. I finally just took apart the whole system and pulled the top of the manifold to do lots of other PM and found the plugged port.

Local mechanic here in Dallas that worked at the Lexus dealership for a long time said that port gets plugged plenty often and was one of the first places they would look on the LX450s. A cheap and easy fix requiring no parts.

Happy to see that the troubleshooting of this problem has advanced so much. When I had the problem, it wasn't so well sorted out.

Keep the Cruiser Faith !

R.

I know some disagree, but I think this is the correct way to go. I took the intake manifold off, cleaned the TB, replaced all vacuum lines, cleaned the EGR and EGR tube, changed the VSV for EGR, etc. I don't particularly enjoy chasing things down, so I would rather just knock it all out at once and try and solve the problem quickly. Mine was a P0401 and more often than not, it seems like it's a VSV for EGR problem once the engine gets warmed up.

 

[super90]

I know some disagree, but I think this is the correct way to go. I took the intake manifold off, cleaned the TB, replaced all vacuum lines, cleaned the EGR and EGR tube, changed the VSV for EGR, etc. I don't particularly enjoy chasing things down, so I would rather just knock it all out at once and try and solve the problem quickly. Mine was a P0401 and more often than not, it seems like it's a VSV for EGR problem once the engine gets warmed up.

Admittedly, that's what I did. I ordered all the parts to just "rebuilt" the whole system at about 125k miles. Once it was apart I found the real culprit (clogged port), but afterwards I knew the whole system worked as it should because I had all new bits in there and I haven't had to monkey with it since (212k mi. now). While apart I also had the injectors ultrasonically cleaned and flow tested, replaced all the heater hoses (PHH included), all new vacuum line, etc. etc. Truck runs like a top.

 

[Chris Wilcox]

Been a year and my code has not returned. Raventai and I have both researched this thing to death and came to the same conclusion it would seem. So there IS at least one sure fix to P0401 in my opinion. New VSV relocated as per above.
Chris

 

[jatree]

I just performed these tests with vacuum pump as the gauge...
Test 1 (T between EGR valve and Intake-to-VSV line) resulted in 0 vacuum
Test 2 (Plug Intake-to-VSV line and read from DS of EGR valve) == very slight vacuum (below 3 inHg)

This is with a new VSV that tested good at 31 Ohm between the terminals... Could it really be a bad new VSV? Or is there another place I should look?

Rather than drive test, this was in Park but still revving up 2,500 rpm.