'96 LHS P0401 error code

Hey are you sure on that engine code number friend.. I cannot find that at all in the code book i can find.
here is one of the multiple links i found and seems none go over p3999

when was the last time the egr valve was replaced ?? could be restricting flow .... to the system... thus clogging up..........
p0401- Insufficient EGR flow
then after replacing it,,, disconnect battery for about 20 minutes and it should reset the system.

Year, Make, Model, and Engine Size?

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

P0401=EGR valve insufficient flow
P0700=transmission control system malfunction
P1739=transmission control module controller circuit

Get the EGR valve checked. It may be that a vacuum line is off. But worst case, say you need a new EGR valve. You can price one at autozone.com. Then find out what a shop would charge for labor to put it in. The transmission codes may be intermittant faults. If your car seems to be running fine, reset the codes and they may not come back until after your test, if ever. If the codes come right back, you'll have to take it to a transmission shop for check out. Any major auto parts store has a code reader that can reset your codes for free.

Just to be clear, have all your work done and then reset your codes. Then you will have to drive your car normally for a few days before taking your DMV inspection. There is a test they will run to see if enough drive cycles (a start, run, and shut down=one cycle) have been accomplished after a code reset. This prevents people from resetting the codes and immediately taking the test without any work being done.

P0401 indicates that the Exhaust Gas Recirculation Flow Insufficient Detected. This can be because EGR is faulty . As you have replaced this then the problem must be with the vacuum line . EGR valve vacuum line which can be broken or blocked. The vacumn ine must bbe checked for leaks or any blocks using an vacumn pump connected the line.

P0420 indicates that the down stream oxygen sensor reading is not steady and it is connected with the code P0401.

Code # p2238 is for the air fuel sensor,you may have a bad sensor the one in the exhaust manifold.

a blinking eng light usually comes with power loss and shaking as the vehicle is misfiring. Scan the vehicle's computer as this would give you a starting point. Codes P0300, P0301, P0302, P0303... would indicate misfires detected in particular cylinders inspect ignition components and repalce as needed

Have a little read of this link, it may help you.

http://www.obd-codes.com/p0401

to ideas come to mind, maybe a bad bulb in the dash (you can take this out (depending on mechanical knowledge)

or find a smaller inspections shop and try taking the car in again in hopes of that they won't catch it

P0401 means
EGR port is clogged or has failed.