Latest member of the P0401 club (x2) (3 Viewers)

Joined
Oct 14, 2020
Messages
92
Location
Charlotte, NC
I recently performed quite a bit of maintenance on the green FJ80 (Dobbie):
  • Flushed the transmission fluid
  • Changed the kick-down cable
  • Changed the shocks
  • Swapped the coils between left and right (were installed wrong before I purchased it)
  • Changed oil and oil filter
  • Changed front and rear axle oil
  • Changed the transaxle oil
  • Flushed the coolant system
  • Replaced external and internal weather strips on all 4 doors
  • Added grease to the Birfields
  • Cleaned the ABS sensors (the ABS light was on)
After all this, I took it for a test drive. The ABS light was still on. Have to address that later. However, the CEL came on during the test drive and the reader showed P0401.

We recently also purchased a triple locked burgundy FJ80 (Gryffin). When it was delivered, the CEL was on with P0401 showing on the reader.

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I know that there has been A LOT written about he P0401, and I have read most of it. However, when I performed the tests in the FSM, I had some strange results:
  • The cap of the EGR modulator doesn't come off on the green FJ80. It does on the burgundy FJ80. Burgundy one is clean.
  • I applied air to both vehicles at Port Q, with ports P and R blocked. Neither vehicle vented through the sides of the EGR modulator.
  • I applied vacuum to the EGR with a vacuum hand pump on both vehicles and it didn't cause either vehicle to run rough or die.
  • Cold, with vacuum applied between the modulator and the EGR on either vehicle, it pulled no vacuum at idle, or 2500 RPM. Also, once it heated up, there was still no vacuum.
So........either I am not performing the tests correctly, or it is telling me that one or several of the components are suspect. I didn't pull the VSV to test it, since I didn't want to pull the upper intake chamber yet (seems like a job).

Some may immediately say "delete it and move on". I don't want to do that. I want to isolate the problem and then decide whether to fix it or not. Any advice?
 
Joined
Jan 31, 2005
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Location
Denver CO
For this one:
2. "I applied air to both vehicles at Port Q, with ports P and R blocked. Neither vehicle vented through the sides of the EGR modulator." - From EG-123 - you did this with the engine off? If air doesn't flow through to the filter side, then the FSM says to replace the modulator.

For this one:
3. "I applied vacuum to the EGR with a vacuum hand pump on both vehicles and it didn't cause either vehicle to run rough or die." - from EG-121/124 - EGR valve might be stuck, not sure if there's a way to clean it up. FSM says to replace. Did you try applying vacuum to port R of the EGR modulator? Do you think your hand vacuum pump is good and giving enough vacuum? Wondering if using a connection to the air intake to pull vacuum might be better?

For this one:
4. "Cold, with vacuum applied between the modulator and the EGR on either vehicle, it pulled no vacuum at idle, or 2500 RPM. Also, once it heated up, there was still no vacuum." - from EG-121 - when cold there should be no vacuum, but when warm there should be vacuum. If you are not getting vacuum when warm then the VSV may not be operating - you will need to dig in further. Some relocate the VSV for easier access down the road.

Sounds like you're doing the right things, but troubleshooting can be a pain. I forget which vacuum connection goes through the plenum with a small hard pipe, but that may be plugged, so worth checking.

This is a good post here:

And here:
 
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Joined
Oct 14, 2020
Messages
92
Location
Charlotte, NC
Thank you very much for the info

2. "I applied air to both vehicles at Port Q, with ports P and R blocked. Neither vehicle vented through the sides of the EGR modulator." - From EG-123 - you did this with the engine off? If air doesn't flow through to the filter side, then the FSM says to replace the modulator.
-- Yes, I did this with the engine off. When you say "filter side", you mean literally the sides of the modulator?

3. "I applied vacuum to the EGR with a vacuum hand pump on both vehicles and it didn't cause either vehicle to run rough or die." - from EG-121/124 - EGR valve might be stuck, not sure if there's a way to clean it up. FSM says to replace. Did you try applying vacuum to port R of the EGR modulator? Do you think your hand vacuum pump is good and giving enough vacuum? Wondering if using a connection to the air intake to pull vacuum might be better?
-- Not sure if it pulls enough vacuum, but I do feel it on the tube and can run the vacuum pressure up if I block the end. I wasn't sure which tube to connect from the air intake. I did connect it to R though.

4. "Cold, with vacuum applied between the modulator and the EGR on either vehicle, it pulled no vacuum at idle, or 2500 RPM. Also, once it heated up, there was still no vacuum." - from EG-121 - when cold there should be no vacuum, but when warm there should be vacuum. If you are not getting vacuum when warm then the VSV may not be operating - you will need to dig in further. Some relocate the VSV for easier access down the road.
-- I found it bizarre that both vehicles acted exactly the same. Either they have the same issue or I am doing something wrong.

Sounds like you're doing the right things, but troubleshooting can be a pain. I forget which vacuum connection goes through the plenum with a small hard pipe, but that may be plugged, so worth checking.
-- Indications are that either all components are bad (hopefully unlikely) or I am not performing the tests correctly.

I am going to start by testing all the vacuum lines for obstructions that might be throwing all the other tests off. Other than that, I am scratching my head.
 
Joined
Jan 17, 2017
Messages
381
Location
PNW, USA
I'm in a similar boat and getting similar results as you even with a new VSV and VM - and this is after cleaning the TB ports. Now I don't have a code but it's also not reading any vacuum where these tests indicate it should.

When the FSM says connect to intake for vacuum - what does that mean?

@GerhardUngerer - If you apply vacuum to the left port of the EGR valve while pinching the right (to the VSV), does it stall?
 
Joined
Oct 14, 2020
Messages
92
Location
Charlotte, NC
It does NOT stall. I found two vacuum lines that were cracked (the other end of the modulator lines). I pushed them back on snugly, planning to replace them. Then I squirted some started fluid on all the vacuum lines, trying to see if I see a difference. None. I cleared the codes and has not thrown a code since. So I will replace those two lines and see what the future brings...

My suggestion to you would be to first look at all the vacuum lines.
 
Joined
Jan 17, 2017
Messages
381
Location
PNW, USA
If it doesn't stall when you apply vacuum directly to the EGR valve with a pump, especially with the line pinched that goes into the intake (this eventually goes to the VSV), then I don't think your EGR valve is moving.

And yup I've replaced a bunch of vacuum lines includes the two from the TB to Vacuum Modulator to no avail yet. I'm sick of it and will try again with a clear head.
 
Joined
Oct 14, 2020
Messages
92
Location
Charlotte, NC
If it doesn't stall when you apply vacuum directly to the EGR valve with a pump, especially with the line pinched that goes into the intake (this eventually goes to the VSV), then I don't think your EGR valve is moving.
That is what I thought also, but cannot explain the code going away now.

I'm sick of it and will try again with a clear head.
I feel you!
 

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