Okay so the p0400 code poped up on me and I can't find the problem. Done changed the egr valve and still the same code pops up. can someone help, what else could it be?

 

97 Subaru Legacy GT

Edited August 25, 20169 yr by Lockett77

So . . . what kinda' car you working on?

97 subaru legacy gt

Vacuum leak or the BPT valve is bad. BPT valve is the black plastic dohickie wih the shiny sticker on top of the manifold.

 

The EGR valves on these almost never fail.

I looked at the BPT and none of the vacuum hoses going to it has air coming through. Is that normal? Same with the hose that attaches to the EGR valve.

I have an EGR code to, so it is almost never the EGR that fails? I wish I could find a sharp and reasonable mechanic locally.  Going to another Auto Zone to have it checked would throw the same codes?

 

I need to pass emissions coming up.

With it running, grab the EGR diaphram valve and cycle it by hand. If the car runs rough while doing that, you have a clogged BPT or the solenoid is not opening to let vacuum to the valve. If it doesn't run rough, possible plugged tube or intake runner.

I have no idea what you are referring to there but will try to figure it out.

I have a 97 legacy outback 2.5. Got the same code. Replaced EVERYTHING, and properly cleaned every hard and rubber line. Solenoid, EGR, and BPT replaced and vacuum tested. Still getting horrible gas mileage and the P0400 code pops up again and again. Even tested the O2 sensors on the multi meter, and they are operating perfectly. What the hell is next? Cat back exhaust? Or black electrical tape overy the check engine light?

This car have a pressure sensor filter? Quick search online revealed that could also cause problems with 0400. I've never had to change one before but might be worth trying for a few bucks that it cost.

I blew it out and the line was clear as can be..

There are two sides of the EGR system, the mechanical side and the ECU monitoring side.

 

If I can cycle the EGR by hand while the car is idling and it acts like it's going to stall, then the valve is working. I will always start by replacing the tiny in line filter that is in the vacuum line going from the intake to the passenger side strut tower. At the same time, I will replace the BPT mounted above the EGR valve. If the code returns, it's likely the vacuum solenoid the ECU triggers to open the EGR valve, is bad.

Out of nowhere my check engine light turned off this morning. Guess the ecu cycled and didn't find anything wrong, so reset itself! Now that I just jinxed myself, it will turn back on next time I start it..

So I have replaced my whole EGR system. Replaced EVERY line, EGR, Solenoids, EVERYTHING. All seems to be functioning fine, running good, but still bad gas mileage. The Check engine light goes off for about 4 or 5 days then turns back on with the same EGR code. Is the next step new exhaust system? The exhaust has 238,000 miles on it, but the motor only has 50,000 on it. I'm stumped. Could it be a bad computer since I used the original one when I replaced the motor, or do you all think maybe the exhaust is just old and full of crud? Any info and or advise would be awesome. Thanks.. 

Did you replace the inline filter that goes to the monitoring portion of the EGR on the passenger side strut tower?

Edited April 11, 20178 yr by Caboobaroo

Yea, replaced that too. That has been suggested a few times. I wonder if Bypassing it would do anything. Hard to believe that that little thing could cause all of these issues. What do ya think?

Have you checked the port in the exhaust manifold.  It could have carboned over.  Remove the egr valve and poke a wire down both ports to make sure it is clear all the way from the inside of the exhaust manifold to the inside of the intake manifold.

Oh yes, did that. Used my "guitar string" pipe cleaners and picks and cleared all carbon build up in all of the lines and ports. The lines that are removeable were removed and thoroughly cleaned, and the ones that can not be removed were cleaned out. I might take it all apart again and see if any loose chunks have gotten wedged in somewhere, but hard to believe on a 50,000 mile motor that this should be such an issue.