OK, I am "planning ahead". What happens if I clean the throttle body, clean the EGR port, and also the port going from the EGR to the exhaust, I am also putting in a new EGR valve (car has 225,000 miles) - and the P0401 code comes up again? Can something else cause that code? What sensor produces the P0401 code?

 

Its not a single sensor that causes that code. The engine computer uses multiple inputs to determine if the exhaust gas is getting into the cylinders. Your fix of cleaning the port will fix this problem. Replacing the EGR is overkill, but keep the old EGR valve. If you go with an aftermarket valve, it could be bad out of the box.

 

Thank you!

I will just remove the EGR valve and clean everything and reinstall (with new gasket) - along with cleaning the upper throttle body as shown in the video...

 

When I did my wife's 2000 Accord F23 EGR, I removed the upper plenum half, and cleaned the port. After I reassembled it, I cleared the code, but it came back, so I replaced the valve too, and it's been good to go since then (about 2.5 years now). From what I understand, you should only need to clean that port once in a life time, or at about 225K miles, as it takes a long time to build up the carbon.