Hello everyone, I'm trying to diagnose my P0400 EGR flow error code. Operating the EGR valve by hand bogs down engine, so valve does something. I can hear a clicking in the solenoid. I replaced the vacuum hoses and cleaned the passages to the best of my ability, but here's what I don't understand:

 

 

The two small EGR related hoses coming off the throttle body, should these be a source of vacuum at idle? I plugged a vacuum gauge into both and got 0 PSI, even thought I took off throttle body to clean the passages out. Should I be getting -20PSI that I am in other places, or am I reading this wrong?

Never mind, I took off throttle body again and saw the lines actually connect before the throttle plate, not after it - meaning there should be no vacuum with throttle plate closed, or wide open. Vacuum should be present at partially open throttle. On with the diagnostic - I measured vacuum before and after the BPT since I already tested the valve and solenoid. These were the results.

 

 

 

 

I temporarily bypassed the BPT and saw that the EGR valve started opening with throttle. I don't know how exactly it works, but it looks to me as if there is an obstruction in the BPT. Going to take it off and see if I can clean it.

It common for the BPT to go bad. Not sure if cleaning is possible, there is a diaphragm inside that controls the opening of the valve based on intake vacuum. The diaphragm can rupture and prevent vacuum from passing through the BPT. If it don't work it just gets replaced.

It common for the BPT to go bad. Not sure if cleaning is possible, there is a diaphragm inside that controls the opening of the valve based on intake vacuum. The diaphragm can rupture and prevent vacuum from passing through the BPT. If it don't work it just gets replaced.

 

Yeah that's what I've been reading online... they are pretty expensive I'm going to see if I can find one in a junk yard, but of course rubber diaphragm exposed to exhaust can only last so long so I can see the risk in getting a used one 

unit may be bad, but check the small nipple on the bottom. It's easy to get clogged.

Also the line that goes from the manifold to the egr unit itself. Another one that likes to clog.

 

O.

unit may be bad, but check the small nipple on the bottom. It's easy to get clogged.

Also the line that goes from the manifold to the egr unit itself. Another one that likes to clog.

 

O.

 

Which nipple is that? On the bottom of BPT? 

 

All the other metal lines I cleaned out to begin with, and the rubber lines replaced with new

Not sure what year and engine you have but I have plenty of intakes with all of the stuff on them.  If it mounts to the intake I most likely have it.

Just wanted to follow up for anyone searching in the future: The BPT was the problem.

 

Another post told me to remove top and look at the white foam stuff inside, and if you see any black it's already bad. I did this and mine had black. I went to junk yard and used the same method to find good ones - only found one where the foam was white, grabbed that and installed on my car. Immediately I saw EGR valve start opening with throttle opening. 

 

This was two months ago or so, no check engine codes or anything since then - so seems to have fixed the issue completely. 

Thanks for the update. Glad to hear its fixed. Never knew the BPT could be taken apart, will have to remember that if I ever need to check one.