Other reasons for P0400 EGR Code?

[MummifiedCircuitry]

I've had the P0400 code since I bought my Montero, the previous owner replaced the EGR valve and EGR solenoid but it didn't clear the code. I replaced the EGR vacuum control valve and checked for vacuum leaks, but the code was still there. Once I cleared the code with a scanner, it would come back after about 20 miles every time. This last weekend, I pulled the EGR valve itself and cleaned it out well, it had some build-up inside. After clearing the code, I drove the rig out to visit some family and back, then around home for a few days without the CEL coming back, approximately 425 miles. Today the code popped up again and I'm wondering if other components would trigger the P0400 code such as O2 sensors? It doesn't really run any differently when the code comes back, it just bothers me that something is malfunctioning.

 

[TheMole]

Try these steps from the fsm:

 

[speedtre]

I had a similar problem on my 99. First I cleanded out the EGR...code came back. I replaced the EGR...code came back. I then cleaned the throttle body with Sea Foam Deep Creep and then Sea Foam intake treament and that sorted it out for good.

 

[alex9528]

Had this problem recently and replaced items you listed. Mine is an 01 ltd but there is a small brass regulator inside the vacuum tube that gets clogged with dirt and this will give you the P0400. This tube is connected to egr solenoid. pull out tube and test it with canned air. I bought new egr/solenoid and actually don't need it. Other mitsu models have this same problem if it is a v6 engine. I just removed mine and not have a problem.

 

[MummifiedCircuitry]

Had this problem recently and replaced items you listed. Mine is an 01 ltd but there is a small brass regulator inside the vacuum tube that gets clogged with dirt and this will give you the P0400. This tube is connected to egr solenoid. pull out tube and test it with canned air. I bought new egr/solenoid and actually don't need it. Other mitsu models have this same problem if it is a v6 engine. I just removed mine and not have a problem.

I just checked and none of the lines coming off my egr solenoid have brass regulators or anything in or connected to them. I blew air through both and there are no obstructions. Some of the vac lines related to my egr are newer, so it's possible it used to have the brass bit you're referencing? Thank you for the info.

 

[MummifiedCircuitry]

I had a similar problem on my 99. First I cleanded out the EGR...code came back. I replaced the EGR...code came back. I then cleaned the throttle body with Sea Foam Deep Creep and then Sea Foam intake treament and that sorted it out for good.

I actually cleaned the whole throttle body about a month ago when I was cleaning the IACV. I had it on a bench and got it spotless with carb cleaner and cotton swabs, so I don't see that being the problem. I'll have to check the manifold differential pressure sensor mentioned in TheMole's post though, I didn't know that was related to egr.

 

[Se7en62]

I actually cleaned the whole throttle body about a month ago when I was cleaning the IACV. I had it on a bench and got it spotless with carb cleaner and cotton swabs, so I don't see that being the problem. I'll have to check the manifold differential pressure sensor mentioned in TheMole's post though, I didn't know that was related to egr.

Did you ever sort out the issue? I know you haven't posted in 6 months, but maybe you'll see this when you log back on.

 

[Monterii99]

Replaced the valve cover gasket and spark plug tube seals on a 1996 Montero SR. Cut the 3 vacuum lines to the throttle body for easier access. Use Mitsubishi OEM gaskets since the FelPro silicone gaskets fail to stop oil leaks when car is running. P0400 code started a week later, after installing new spark plugs, new spark plug wires, intake manifold, and new vacuum lines. Replaced the MAP sensor - P0400 returns after 20 miles. P0400 returns after replacing EGR valve and PCV valve. Found a tiny brass regulator valve inside the vacuum line from the EGR solenoid to the EGR vacuum controller. Cleaned throttle body. Cleaned brass regulator and replaced in rubber vaccuum line- P0400 still occurs. Replace EGR solenoid (OEM). After 8 miles - P0400 occurs . Reset OBDII error code. Montero has various sizes inside diameter (ID) vacuum hoses. Make sure new vacuum hoses have same ID used in Montero. The new vacuum lines to throttle body - were looser than OEM and easily pulled off-Replaced with NAPA NBH H-174 fuel hose. Used Autozone 50209 Amor Mark vacuum hose to connect the EGR valve. Replaced hose with brass regulator valve with hose without regulator.
No error codes after 100 miles. The vacuum lines must fit tightly. Apparently a loose fit will cause P0400 emission
error code. A Mitsubishi tech said the brass regulator was not needed.

 

[Monterii99]

Did you ever sort out the issue? I know you haven't posted in 6 months, but maybe you'll see this when you log back on.

I had the same P0400 problem

 

[MummifiedCircuitry]

Replaced the valve cover gasket and spark plug tube seals on a 1996 Montero SR. Cut the 3 vacuum lines to the throttle body for easier access. Use Mitsubishi OEM gaskets since the FelPro silicone gaskets fail to stop oil leaks when car is running. P0400 code started a week later, after installing new spark plugs, new spark plug wires, intake manifold, and new vacuum lines. Replaced the MAP sensor - P0400 returns after 20 miles. P0400 returns after replacing EGR valve and PCV valve. Found a tiny brass regulator valve inside the vacuum line from the EGR solenoid to the EGR vacuum controller. Cleaned throttle body. Cleaned brass regulator and replaced in rubber vaccuum line- P0400 still occurs. Replace EGR solenoid (OEM). After 8 miles - P0400 occurs . Reset OBDII error code. Montero has various sizes inside diameter (ID) vacuum hoses. Make sure new vacuum hoses have same ID used in Montero. The new vacuum lines to throttle body - were looser than OEM and easily pulled off-Replaced with NAPA NBH H-174 fuel hose. Used Autozone 50209 Amor Mark vacuum hose to connect the EGR valve. Replaced hose with brass regulator valve with hose without regulator.
No error codes after 100 miles. The vacuum lines must fit tightly. Apparently a loose fit will cause P0400 emission
error code. A Mitsubishi tech said the brass regulator was not needed.

Thanks for bringing this up, I'm going to give it a try. Do you figure about 3 feet of the NBH H-174 will cover it?

 

[Monterii99]

3 feet should be enough - the NBH H174 is reinforced (will not expand) and will only work as the 3 vacuum lines from the throttle body. Use Autozone 50209 for the line to the EGR valve. I did reused some of the Mitsubishi hoses as there is a variety of ID (interior diameter) tube sizes used. No P0400 code so far.