How to check the EGR valve with live data
Jerky at mid revs and smoky — read two numbers instead of stripping the intake.
Find two readings: EGR command and EGR error
The first shows how far the unit ASKS the valve to open. The second shows how far the actual position differs from that request. Read them together: the command alone tells you nothing.
Check at idle: the command should be zero
At idle and at full throttle recirculation is not needed and the unit does not ask for it. If the command is not zero at idle and the engine shakes, the valve is hanging open and exhaust enters the intake when it should not.
Drive at mid load
Recirculation is needed exactly there: steady cruise, mid revs. The command should rise while the error stays near zero. A steady gap means the valve is not going where it is asked — usually because of soot.
Tell a sooted valve apart from blocked passages
The valve may open honestly while the gas still has nowhere to go: intake passages clog with soot over the years. The sign is a command present, error small, and no change in how the engine behaves at all. Codes P0401 and P0402 are about insufficient and excessive flow.
Do not blank the valve just to make the code go away
A blanking plate removes the code and adds two problems: combustion temperature rises and the particulate filter, if fitted, clogs faster. Cleaning the valve and the passages costs less than the consequences.