I live in the Northeast, several months ago my MIL lamp posted a P0401 code “EGR Insufficient Air Flow” The following parts were tested and replaced where necessary: VSV for ERG, EGR Vacuum Modulator, and Vacuum Hoses. The passageways for the EGR valve were also checked for carbon buildup but it was clear. The EGR valve was OK.
The MIL Lamp was reset, however after driving approximately 30 miles the MIL lamp tripped another P0104 code. A qualified technician checked the system again but to date no reason could be found to trip the code.
Since nothing could be found I was wondering if this might be a possibility, could a cold running engine cause the MIL lamp to post a P0401 code. I noticed that this past winter with extremely cold weather that my engine was running below the normal temperature, around 160 degrees, since coolant temperature plays a part in determining EGR function I was wondering if a faulty thermostat or coolant temp sensor would cause the EGR system to not work properly? It’s the only other thing I could think of as a remote possibility. Before I change the thermostat and or Temp sensor I wanted to get your opinion?
Any input would be appreciated.