I have a p401 code on my 98 avalon, indicating low egr pressure. What do I need to replace

Possible Problems
EGR valve stuck closed <= Most common - Clean EGR valve
EGR Vacuum Switching Valve (VSV)
Open or short in VSV circuit for EGR
EGR valve position sensor open or short circuit
Vacuum or EGR hose disconnected
EGR valve position sensor
Manifold absolute pressure sensor malfunction <=Test MAP sensor if present
ECM