P0401 Troubleshooting Question - Replaced Vacuum Solenoid

[mike665]

I have a 99 4 cylinder Camry with a P0401 engine code on. I replaced the vacuum solenoid after cleaning the old one did not help.

With the new vacuum solenoid, the light comes back on and starts to run terrible. When I left of the gas while driving the engine does a VERY noticeable hesitation. This did not happen till 100+ miles with the new part. I pulled over an disconnected the hoses and reset the engine code and it ran fine again.

When I put the old vacuum solenoid in, this goes away even though the engine light again comes back on. With this old part, I never had a noticeable difference in the way the car ran.

Does this sound like a bad part? Or does it sound like the problem is deeper rooted then the vacuum solenoid.

Thank you in advance!

[xtremexnyc]

Did you check if the EGR valve is clogged or not functional. You might want to look into this as well.

[fenixus]

go here:
http://www.camrystuff.com/manuals/Gen4/Diagnostics.pdf

go to page 105, it says possible cause for P0401:

P0401 DTC detecting condition:

After engine is warmed up, intake manifold absolute pressure
is larger than value calculated by ECM while EGR system is
ON
(2 trip detection logic)

P0401 Trouble area:

-EGR valve stuck closed
-Open or short in VSV circuit for EGR
-Vacuum or EGR hose disconnected
-Manifold absolute pressure sensor
-VSV for EGR open or close malfunction
-ECM

check them all and you most likely will find the root cause of your problem. cleaning EGR (after unbolting it) is also a good idea, might be clogged, or the pipe or other vacuum lines might be clogged, so EGR valve operates poorly.
but first of all make sure you have no vacuum leaks and MAP sensor operates correctly. you will need a hand vacuum pump to take the real life readings. you can also use a laptop with obd2 software to get direct MAP reading from ECM.

DIY on unbolting EGR valve:
DIY : EGR Valve removal

good luck!