P0401 - Please HELP

[GerhardUngerer]

Hi guys, I got the P0401 error on my truck and when I looked the EGR Modulator, I found the issue on the left. No problem. I bought another, installed it, and a week later I get the picture on the right. What is causing this? At $120 a pop, those modulators are not cheap.

Is it as simple as the tube pops of and fries the modulator with exhaust gas? Do I just replace the tube also? Maybe clamp it on?

 

[open country]

Quick search and it seems like common cause is increased heat/backpressure in exhaust that blows through the cap.

Clogged cat, high EGT's, obstruction - look downstream.

 

[SHIfTHEAD]

Yeah, found this thread where someone had a similar issue. I use the Hudd Expo stuff on my rig, but I also just had replaced all the exhaust/cats too:

EGR Vacuum Modulator Meltdown following EGT Delete

93 FJZ80--LandCruiser-- Federal Spec So a couple of months ago I noticed that some vacuum hoses on my engine were cracked and coming apart. Who knows how long they had been that way. After researching I discovered that these were EGR vacuum hoses-- hoses that go between the EGR vacuum...

forum.ih8mud.com

 

[Malleus]

Gerhard, have you cleaned the upper Intake?

 

[GerhardUngerer]

Made an appointment at Meineke to test the cat. Got there and the guy told me "we are running long on another job, come back some other time". Then drove down to Black's Tire and asked them if they could check it. Dude told me "No". Does anyone work anymore? Or want business? Or know how an economy works?

 

[Malleus]

precious few

 

[GerhardUngerer]

Gerhard, have you cleaned the upper Intake?

I have not. Will that cause the exhaust back pressure? I ran the vacuum test and it passed with flying colors. Then did the same at 2500 and it was rock solid in the green also.

?????

 

[GLTHFJ60]

How exactly was the shop going to "test the cat"?

You could rig up a pressure gauge to the manifold, but finding a reference would be a problem. After a relatively long drive at high ish throttle, is the cat glowing? Maybe lower felt power than before?

 

[Malleus]

I have not. Will that cause the exhaust back pressure? I ran the vacuum test and it passed with flying colors. Then did the same at 2500 and it was rock solid in the green also.

?????

P401 does not mean there is exhaust back pressure. It simply means there is insufficient flow to the EGR sensor. IME, this is most likely due to a clogged port between the sensor and the valve. That passage is at the top rear of the upper intake, directly between the sensor and the EGR. A vacuum pressure test will not expose this blockage, since the port is open only between the sensor and EGR.

As to your "exploding" EGR modulator valve, that's a new one on me.

FWIW, I have this same problem; I'm ignoring it until I pull the manifiold to clean it thoroughly. If you want to clean it, use carbon-off:

 

[Green Hell Mustang]

How exactly was the shop going to "test the cat"?

Simple! You see if it responds to "pspspspspsps"

 

[jfz80]

Should be able to use an IR temp gun on the pipe both pre and post cat to compare. Shoot the temps of the inlet and outlet pipes 1-2” from the flange or cat itself if direct welded. Post cat should be hotter indicating it’s functioning.

 

[lumbee1]

Should be able to use an IR temp gun on the pipe both pre and post cat to compare. Shoot the temps of the inlet and outlet pipes 1-2” from the flange or cat itself if direct welded. Post cat should be hotter indicating it’s functioning.
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Thanks for posting this.