My engine is throwing a P0401 Insufficient EGR Flow error code. The engine was running smoothly, but with the error code I would not pass California smog inspection. The engine was running very smoothly so it was obviously not a major issue with how the engine was running.
After troubleshooting the EGR Valve, vacuum switching valve, and vacuum modulator, I found that the vacuum modulator was defective.
I replaced the vacuum modulator and drove two hundred miles of mostly city driving to reset the computer. Even though the engine was running pretty smoothly previously, I noticed that the engine was running even smoother after replacing the vacuum modulator.
When I brought it back to the smog test center, it immediately threw the P0401 error code again. The technician suggested cleaning the EGR down tube and driving another two hundred miles mostly city miles to let the computers reset.
What do you suggest I test next?
Also, I have noticed some mechanics refer to a bottom mounted vacuum switching valve but mine appears to be top mounted. Are there two vacuum switching valves on this vehicle, or are some top mounted while other Camry's have them on the bottom?
It has been many years since I have done my own auto repair. Back in the 1980's and early 1990's, I enjoyed do my own work on mostly 1960's to mid 1970's cars. This is my first time working on a car with (relatively) modern emissions controls. I have an engineering BS and MS and working knowledge of automotive systems, and consider myself a mid-level home mechanic.
Saturday, November 14th, 2020 AT 2:29 PM