1999 5.4 liter. Check engine light on. Code P0401(EGR too little flow). Runs rough in o/d at 35-45mph, skipping some, terrible gas mileage.

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.

The EGR valve is in a very difficult spot to work on. If the EGR is bad it will set off the check engine light and make the vehicle run rough or stall at idle. It really doesn't make it run rough while driving or accelerating. What are the conditions when the car runs rough?

The code P0401 means P0401 Exhaust Gas Recirculation Flow Insufficient Detected.
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airbag reset tool also check fault code!

OBD-II Trouble Code P0401 - Insufficient EGR Flow

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR. You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.

A code P0401 most likely means one or more of the following has happened:
The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
There is a blockage in the EGR (tube), most likely carbon buildup
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

Check it and keep us updated. Hope this helps (remember to rating this free answer).

need to replace exhauust gas recirculation (EGR) valve....code p0401 reads EGR insufficient flow detected .............(so it is probably not opening properly.hope this helps you....thanks for using fixya.

Are you reset the stored codes there? The EGR (Exhaust Gas Recirculation) valve controls an engine's emission of smog-causing nitrous oxides, or NOx. Its job is to route a portion of the exhaust gases back into the intake manifold. That lowers combustion temperature to below 2,500 degrees Fahrenheit - the temperature at which NOx gases form.

EGR flow is controlled by the engine's computer, which opens or closes the valve as needed. The EGR system is, for the most part, in the "out of sight, out of mind" category, and typical doesn't require regular maintenance. But if it gets clogged with carbon deposits, you'll see your "check engine" light come on, and a code (perhaps P0401 or P0402 or P0403) will show that there is insufficient flow. That typically results from a vehicle being driven persistently on short trips that don't allow the engine to fully warm up. Flow problems also can be caused by carbon buildup due to failure to change the oil frequently enough.

A clogged EGR valve not only results in higher emissions, it can affect fuel economy and cause rough idling - even serious engine damage. Valves can usually be cleaned, but replacement is often recommended.

About thie generic fault code, I suggtes check this description and tips for solution information: DTC-P0401-Tests (keep in midn that this code applied for alot brands, Hyundai included).

Keep us updated.

p0401 is egr flow insufficiant. check or remove and clean egr and port. and also check the vacuum lines to egr. Insufficient EGR flow frequently is caused by clogged EGR passageways.

1. po401 refers to an insuffient flow of EGR gasses
2. locate egr valve
3. with engine running at idle
4. on the underside of the valve you can access the diaphram.
5. wearing glove if ness
6. lift diaphram while idling
7. does engine stall or run very rough?
8. if not remove valve
9. start engine
10. you should hear a very large vaccum leak and exhaust noise
11. if either are missing investigate cause
12. if ok reassemble.
13. locate DPFE sensor
14. inspect sensor for damage
15. inspect hose to sensor for damage
16. replace sensor

I had an OBD II 401 code and fixed it by cleaning out the EGR vacuum line in the intake manifold. I removed teh EGR Valve and the set screw below it. i used a rifle cleaning brush and one length of the rod. Then I replaced teh set screw. I started teh engind and let the vacuum **** some carb cleaner through the front port hole. when it was sucking good I replaced teh EGR valve and reset the codes. That fixed it.

The egr valve has insufficient flow, take it off, or have it taken off, and clean the under side of it, there might be a port clogged, or the diaphram inside is leaking, in which case the valve will need replacing.