No vacuum to the EGR valve. The line to the passengers side is clear. EGR valve gives a Check Engine light as a result.

• First you want to open up the hood of your car
• Find the engine diagram sticker on the inside of the open hood and identify the mechanism that is labeled "EGR Solenoid" on the sticker.
• Find the "vacuum line" on the sticker diagram and identify its color. This is the line that runs from the EGR solenoid to the EGR valve.
• Locate the vacuum line inside the engine compartment of the vehicle toward the front of the driver's side. The vacuum line will be the same color on the vehicle as it is on the diagram.
• Follow the vacuum line from the front of the vehicle where it connects to the EGR solenoid through the conduit that carries it to the EGR valve at the rear of the engine compartment. The easiest way is to track the uniquely colored vacuum line along the path between its two connection points. The vacuum line connects to the EGR valve, which is the disk-shaped object located at the rear of the engine compartment
  on the driver's side.

EGR vacuum solenoid is located below your EGR valve. Center your self on the engine, look between the rear of the engine and your firewall. You can see your the top of you EGR valve, there will be a small vacuum hose connected to the top. Follow that small hose straight down from your EGR valve and it connects to the solenoid. You can see the solenoid better from beneath the car. May have an orange connector. Hope this helps.

It's usually the pressure sensor. They get contaminated and give faulty readings.

it may help to tell what engine you have. P0401 doesnt mean the egr valve was bad, it means the egr isnt opening for some reason OR not flowing. Egr valves rarely are "bad" check if all vacuum lines are connected and clear. the egr vacuum solenoid is famous for being bad. als make sure the passage from the egr valve to the intake manifold is clean and flowing. Its like flushing a toilet thats clogged.. All the valves are working, but its not flowing.

need a new egr valve go to the parts store and buy one and a couple of small wrenches you will find that is easy PS make sure it was plugged in with a hose look up part on auto zone.com so you know what part your looking for

Before you unpack the EGR you might be able to save the old one by cleaning it an then collect a refund. The purpose of the EGR is to supply a measure of exhaust gas to the intake mix so that the charge delivered to the engine is reduced in oxygen. This reduces the ignition temperature and prevent nitrous oxide formation in the exhaust. The EGR valve has two ports in it side by side. The one to the exhaust is gated by the valve and the other is connected to the intake. The valve is pulled open by a diaphragm acted on by a vacuum line from the intake manifold. The EGR valve is often monitored and regulated by differential pressure feedback exhaust DPFE sensor that lies upstream on the vacuum line leading to the EGR. If this DPFE fails it will report the same EGR light. Remove your EGR valve and plug the open EGR intake port on the manifold with a cloth and reconnect the vacuum line to the EGR valve. Start the car and now watch the action of the EGR valve. It should seen to open and close depending on engine demand. If it looks badly coked, spray it liberally with carb choke cleaner and wipe with a cloth until everything is polished metal. If the EGR looks good and is obviously working take a long look at the DPFE sensor; DPFE sensors have a reputation for failing many more times more often than the EGR valves they monitor.

Check your bank 2 plugs for colour (do they look hot like they running hot ). Check you EGR Exhaust Gas Recirculation valve (looks like a 80mm diameter spaceship with a vacuum line to the top of it) If this remains closed the engine runs very hot and causes misfire. Possible causes are EGR not opening are 1) perforated diaphragm 2) encrusted valve stem 3) clogged exhaust gas feed pipe. A quick check for function: run the engine and remove the vacuum tube. The engine note should change as the tube is connected and then disconnected. Also pushing on the underside of the EGR with your fingers to lift the diaphragm to open the valve should also result in change in engine note. If its not working just disassemble the EGR and clean with carb cleaning spray, also clean the exhaust gas feed pipe likewise.

Hello Malcolm.
The vacuum line to the EGR will certainly cause your check engine light to come on.
The vacuum hoses on these cars become brittle with age, I generally replace broken lines with a quality rubber hose available at your local auto supply.
The check engine light may take a while to turn off without clearing service codes.
If the light is still on after a couple days of driving you may have other issues turning on the check engine light.
Hope your repair goes well for you.

There is a VSV (vacuum switching valve) , usually mounted on the back side of engine block, under the intake manifold, as well as the map sensor, that can also cause that code if one or the other is faulty. It takes some pretty detailed troubleshooting to confirm this in some cases, so if that's not in your line of work, you may have to have it properly diagnosed, or take a 50/50 shot at which one first.

The EGR valve is located on the intake manifold, it has a single vacuum line going to it, are you sure it is the valve and not the vacuum control valve that opens and closes the EGR? You provided no year or trouble code, so hope this answer is correct.

Pull the EFI fuse for 5 minutes to clear the check engine light