How to repair the code p.0401 EGR system low.Checked EGR valve .Ok , EGR modulator . Ok, EGR VSV .Ok, Cleared the code, road tested abount 15 mins , Check Engine lite come back on again with same code p.0401

code p 0401 refers to exhaust gas recirculation (EGR) system--insufficient flow detected ===causes --hose leak/ blockage--basic setting not carried out if applicable ---wiring---EGR valve ---EGR solenoid --ECM
take it to an accredited service centre that has experience on your make of vehicle , tell them the fault details and get a proper diagnosis to determine the fault and a quote

the exhaust path there must be clear
end to end, its NOT air that is EGR fail for exh. flow, for EGR only.
which engine, ?????
no 2 engines made use the same flow.
so..........????????

P0401-Insufficient flow in the exhaust gas recirculation system (EGR-valve). Check your gas cap for cracked seal, check EGR valve (make sure all vacuum hoses aren't leaking), check also VSV (vacuum switching valve) for proper operation. Its best to get an owner's manual or an experienced mechanic to diagnose!!hopefully this helpd

It means that the egr valve is working, the problem is a very common one, it's the egr modulator valve and to some extent the vacuum switching valve(VSV) for the egr valve, the modulator is attached to the egr valve, remove it and if air can pass from the bottom port through it is defective, in that case replace it and see if it takes care of the problem, if the valve is ok the egr
vsv should be replaced.

Check for air leak into system after MAF.

Check for

vacuum leaks on intake manifold,

the air tube between the air filter.

intake manifold vacuum hose.

===
clean throttle plate with Berryman carburator cleaner

SEE sample picture HERE
===


Check for loose or no connected vacuum hose(s).


Take it for a test drive.


Please rate my answer if it's useful to you.


Cheers,

Mustgo

There is a vsv (vacuum switching valve) located under the intake manifold that goes bad very often causing this code. Its hard to get to. Follow the hoses from the black plastic round valve(egr modulator) you see next to the EGR valve to find the vsv.

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.

Code on diagnostics p0401:

What is going on?
Exhaust Gas recirculation low flow detected means that: there is vacuum problem in the EGR system - between the combustion chamber, EGR valve (mechanical - blown up diaphragm or clogged airlets/hoses) , EGR Modulator Valve (mechanical - blown up diaphragm, dirty EG/air filter or clogged airlets/hoses) and Vacuum Switching Valve ((mechanical - blown up diaphragm or clogged airlets/hoses OR electrical - VSV not properly synchronizing with the ECM, for instance).

Effects?
This causes the combustion chamber temperature to increase and produce Oxides of Nitrate (NOx) that is out of an acceptable emission range. This triggers the Malfunction Light (check engine light) to stay on (after a couple of driving cycles)!
Solution: Focus on EGR airways (hoses...) and organs (EGR valve, EGR Modulator, VSV), clean, check or replace the defected one. VSV seems to be criticale as it plays electrical & mechanical function. Once the repair is done, Clear the P0401 code using an OBII scanner.

I'm assuming that it is a four cyl.The p0401 code is for insufficient egr flow.Most of the time it is the egr vsv valve (vsv means vacuum switching valve)which is what controls the vacuum to the egr valve to open it.It is kind of hard to get to as it is on the block under the head on the back side.If you follow the hose from the egr valve it goes to the vsv.I have also seen mice eat holes in the vacuum line which would also give you problems.I hope this help and let me know if you have anymore questions

HI.....
The problem on your Vehicle related with the VSV.
VSV . VACCUM SWITCH VALVE..


But the problem is you have 3 VSV On your car.
And all of 3 affect the Emission or smog TEST.

1---- EGR VACCUM SWITCH VALVE
2-- EVAP VACCUM SWITCH VALVE
3---- VAPOR PRESSURE SENSOR VACCUM SWITCH VALVE..

All are located on Left side of Engine compartment.
the EGR VSV on left side of the angine.

Are a Small selenoid with 2 small hoses and one connector of 2 wires.

Ok.. But I recomend get the Vehicle SCANNED for get the right codes.
You can go to some autoparts, Advance, Autozone, Napa, Pepboy's,
They scan your vehicle with no charge , is just a complementary service.
With the Codes you will FIX or REPLACE the right part.

OK... I hope this hlep on your problem.
If you need more information I will able to help.
Thank you for use fixa..