It has been a week of work by Honda and still no emmissions inspection. The Check Engine light is on and won't clear. P0401 was the code. EGR insufficient flow. The tech cleaned the EGR ports thoroughly but code did not clear. Next issue was a defective computer. That was replaced today but there's still a pending code that shows up. Any advice that I can pass along to the Honda tech? The car is a 1999 Honda accord LX coupe, 4 cyl 150k plus miles. Shame of it is that the car runs very well.

 

was the egr valve replaced also? I've done numerous egr cleanings and i always replace the valve with it and never once have had an issue, knock on wood lol. but also wondering if the tech actually got the whole port cleaned out. top of the manifold has to be taken apart to get to it...

 

The typical point of EGR clogging is in the upper half of the intake plenum behind the throttle body. The EGR port comes into the intake plenum and makes a sharp hard turn into the large portion behind the throttle body. That is where I have found the clogging on this vintage Accord. This can be fixed by removing the upper half of the plenum and cleaning the port. Shouldn't take more than a couple hours.

Suggest this to the shop just to make sure. The port being clogged can be confirmed by removing the EGR vavle, running the engine and seeing if the engine reacts to what should be a large vacuum leak. If not, you know the port is plugged.

The P0401 monitor watches the MAP value as the EGR valve is commanded open during a long decel from high speed eg, getting off the freeway. If the MAP value increases, the port is considered free and no DTC is set. If the MAP value doesn't increase, the port is considered plugged and the DTC is set.

 

I replaced the EGR valve myself a few months ago. They said it tested fine. Also, they did the cleanout that you guys suggested and somehow, the check engine light did not clear. They said they have troubleshooting step 26 or 27 to attempt tomorrow am.

 

Are you sure they actually cleaned it out? And I dont mean a half-hearted attempt. These upper plenums usually HAVE to be removed from the lower plenum in order to clean it out thoroughly. Its my opinion Honda screwed up when they designed this intake with no access plate!

 

If someone told me they had to perform steps 26 and 27 of the troubleshooting for a P0401 I would assume they don't know what the hell they are doing.

 

Which cars are this exactly, 'cause when I took my intake manifold off to clean and install new gaskets the egr ports don't appear to ever come in contact with the upper plenum. I cleaned out the lower manifold egr ports for a few hours until I could spray water into the egr port and tilt the manifold enough to see it come finally come out all four intake runner head-side. It took a while and some dirt coming through until it was clear they were pretty free.

I know the most clogging I found was in the cylinder head itself. That thing was almost completely closed. It took some work freeing that up.

 

what size pipe are u running if its to large u wont have back pressure to make the egr system work correct

 

 

The EGR port goes up into the upper plenum behind the throttle body. The exhaust gases then distribute to each of the cylinders equally. The upper plenum behind the throttle body is a cap that comes off fairly easily. You will most likely find the blockage where the port finally goes into the upper plenum.