P0401 Buick - EGR valve test OK

Question

What else could cause a P0401 error code if the EGR on a 2002 Buick Century does have 12V across terminal 5 on the EGR Valve terminal (# 1 pin on the harness side) and 5.0 V on terminal 4 (pin 2 on the harness side).
Also the EGR sensor (cross terminal 2 and 4) & EGR solenoid (cross terminal 1 & 5) does not show open (continuity).

This is on a 2002 Buick Century 3.1 engine

Answer 1

P0401 Exhaust gas recirculation flow insufficient detected

When you have this code condition it means the EGR passage is plugged, remove the EGR clean out the passage up to the throttle body

When P0401 set, the EGR passage is plugged, you can use a cable wire and run it through the EGR passage up to the throttle body to clear the build up of  carbon