Trouble Code P0401?

po 300 means multiple misfire any # 1 2 3 or 4 ck plugs , wires and ck compression .. and po401 i guess is egr system malfunction .. replace vacum switch valve for egr wich is on the back of the engine close to power stering pump around that area . did help ?

retrieved code P0401 insufficiant egr flow detected. would like to know correct repair procedure.

A code P0401 most likely means one or more of the following has happened
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
Possible Solutions
In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.
Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's,There should be a noticeable difference in RPM's with the EGR open
Clean out the EGR valve and/or tubing to remove deposits
Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)

1999 Toyota Camry 4 cyl Front Wheel Drive Automatic

code p0401 will not go away. Changed all the components of the egr system and made shure all the passages were clear.Code p0401 still comes back. What is the problem and what monitors the egr flow?

OK so this is an EGR insufficient flow detected. This can be one of the following. EGR Valve, EGR Vacuum Switching Valve (VSV), Map Sensor, bad ECM or a vacuum hose disconnected or cracked or a short in the wiring to the EGR VSV. I can help with some testing but I need to know how comfortable you are with doing some tests and I also need to know if you have a scan tool that will allow freeze frame while driving and do you have a digital multi meter. Let me know what parts you did replace from the list above too. Thanks.

My car has had the check engine light on. Excessive exhaust smell inside car. Throws code p0401. I have changed EGR valve. the air intake hose has a pretty bad leak too. I need to replace. Could this be causing all the trouble? I am going to replace regardless, but want to know if there may be another issue I am missing. I also had replace a part next to the EGR valve that has three vacuum lines hooked up into it. It does not bolt on or anything just snaps into a bracket that holds it in place.

misfires can be anything like a sensor injector. the 401 code is EGR is not working, vacuum leak , map sensor or ECM. I am sending a picture of what I think you may have replaced, it does have an electrical connection as well. so it may be hooked up wrong or something similar.

I keep getting this code, even though I have now replaced ALL the components in the EGR system: EGR valve, EGR modulator, EGR Vacuum Switching valve (VSV), and all 5 of the EGR vacuum hoses. I used genuine Toyota parts. All ports and pipe are clear. Both EGR gaskets were replaced. I am getting 12 volts at one of the two terminals that connects to the VSV. Don't know what else I can do. I'm having no other codes or problems with the car. Could it be the ECU is bad anyway, even though there are no other issues? P0401 code

These codes can be caused by a faulty EGR valve here is a video that shows how to test it with the location of the valve in the diagrams below

https://youtu.be/DqUCbbKdWf4


Check out the diagrams (Below). Please let us know what happens.

Yes, I know all of those tests. THE PARTS ARE ALL NEW GENUINE TOYOTA PARTS. The hose from the intake to the MAP sensor is not leaking, or plugged, and the MAP sensor holds vacuum when applied. I erased the codes and went on the Toyota EGR drive cycle and followed it exactly. It always trips the pending code during the drive cycle and the it becomes a current code on the 2nd drive cycle. The 5 EGR vacuum hoses are routed correctly.

did you check the vsv likit said in second pic and test vacuum through it? is the egr plugged or partially plugged including passageways. it also can be a bad ecm.

Yes, I did. All the parts are new Toyota parts anyway. Nothing is plugged up. Is there a way to check using a multimeter to see if the ECU is switching the VSV on/off? I do get 12 volts at one of the terminals on the plug that connects to the VSV. Is the other terminal supposed to get 12 volts at times to "ground side switch" it? I'm not sure how that can be tested. Is there a way to test the ECU first?

the pink wire on vsv sensor goes to port 7 on pcm so check that for continuity. the other wires tie in to different sensors as you can see in pic. the second pic with violet wire leads to pin 8 on pcm do the same with that. if everything is getting vacuum then I'd have to go with ecm isn't sending power to operate the system which a pro will have to install due to security systems in them. icannot send the wiring diagram as it's to big so if you want to delve further then you can either buy a manual, rent one from here under manuals for your car and I think they allow you for a week as I'm not sure or see if a library has one for it.

It was the ECU. I went to the junkyard and found one for $39. I installed it and the car started and drove fine. After completing the EGR drive cycle, the readiness monitor completed and there is now no more P0401 code. I didn't have any problem with security or anything else with replacing the ECU by myself. Maybe it's newer cars in which that is the case. Anyway, the problem is fixed with a replacement ECU.

My engine is throwing a P0401 Insufficient EGR Flow error code. The engine was running smoothly, but with the error code I would not pass California smog inspection. The engine was running very smoothly so it was obviously not a major issue with how the engine was running.

After troubleshooting the EGR Valve, vacuum switching valve, and vacuum modulator, I found that the vacuum modulator was defective.

I replaced the vacuum modulator and drove two hundred miles of mostly city driving to reset the computer. Even though the engine was running pretty smoothly previously, I noticed that the engine was running even smoother after replacing the vacuum modulator.

When I brought it back to the smog test center, it immediately threw the P0401 error code again. The technician suggested cleaning the EGR down tube and driving another two hundred miles mostly city miles to let the computers reset.

What do you suggest I test next?

Also, I have noticed some mechanics refer to a bottom mounted vacuum switching valve but mine appears to be top mounted. Are there two vacuum switching valves on this vehicle, or are some top mounted while other Camry's have them on the bottom?

It has been many years since I have done my own auto repair. Back in the 1980's and early 1990's, I enjoyed do my own work on mostly 1960's to mid 1970's cars. This is my first time working on a car with (relatively) modern emissions controls. I have an engineering BS and MS and working knowledge of automotive systems, and consider myself a mid-level home mechanic.

Thank you!

I noticed that the two vacuum hoses connecting the throttle body and the vacuum modulator are showing aging signs (surface cracks) but appear to hold vacuum. They seem to be easy parts to replace to rule out vacuum leaks there. Do you concur? If I were to replace them, do I need to use genuine Toyota parts, or can I use equivalent lengths of generic tubing from my local parts store?

Get the ones at auto parts stores. then try cleaning the EGR tube like mechanic said.
https://www.2carpros.com/articles/how-exhaust-systems-work

Thank you HMAC300. Do I need to remove the EGR Valve from the intake manifold to clean the EGR tube, or can the EGR tube be removed/cleaned with the valve in place?

take the valve off and clean it that way and check pintle valve on EGR it may be clogged or not working. Try putting vacuum to it see if it does or not.

My previous tests applying vacuum to the EGR valve caused the engine to stumble and/or stall. I think the EGR valve is working okay. I will take a closer look when I have removed it. The nuts to the intake manifold studs came off easily. I am currently soaking the bolts that hold it to the bottom tube in penetrating oil as they are quite frozen.

I have changed the two Vacuum Modulator to Throttle Body tubes.

After removing the EGR Valve, I looked into the EGR port on the intake manifold and down the EGR tube. While there is a little carbon buildup, it is nothing significant. It is possible there may be more buildup at the bottom of the tube as I cannot easily reach where it attaches to the exhaust manifold.

I tested the EGR Valve and it appears to be okay. The diaphragm looks solid. I pushed it up and put my finger on the port. It held it in the up position until I released my finger ten to fifteen seconds later. Is it worth replacing while I have it off? I have heard they last quite a while. I have to replace the EGR Valve gasket as it broke during removal.

While at the parts store looking at a replacement EGR Valve, I noticed that the range of motion on my old valve in the passageway was not as much as the new one. The diaphragm appeared to have full range of motion.

I decided to replace the EGR Valve. Upon startup, the check engine light did not come on. I will drive around the car for two hundred miles and bring it to be smog tested. I will update when that happens.

Do you have any other suggestions? I think I am approaching the limit of what I can do in my driveway. Thanks!

Hello,

Here is a test you can do to see if the EGR is getting exhaust. Remove the valve and start the engine for a second and see if you hear exhaust coming out, you will know it becasue it will be loud.

Please let us know what you find.

Cheers, Ken

Replacing the EGR Valve allowed my car to pass the California smog test. As a side benefit, though the engine was already running pretty smoothly, each successive step (replacing the Vacuum Modulator, replacing the EGR Valve) had the engine running even smoother.

The range of motion difference between the old and new EGR Valve in the exhaust gas passage didn't look like a lot, but it must've made a difference operationally.

Thanks to HMAC300 and 2CARPROS KEN for their advice!

SImple question that I hope has a simple answer. I am looking to pinpoint the problem so I don't get overcharged for the repair. So my question is, what does error code P0401 really mean? It says EGR Flow Insufficient Detected but what does that really mean? What part actually failed if any? How much would something like that cost to get fixed?

im giving you what most likely is the problem. the egr solenoid fail on this car frequently and should cost about 150 to 200 to repair at a shop

Good to hear, please use 2CarPros anytime we are here to help.

Cheers, Ken

Is this something that I could fix or is that not recommended?

you can fix it. now i cant say for sure this will fix it but in most cases it does. the valve is located at rear of engine and you must access it under the vehicle. not alot of room to move.

I removed and cleaned an egr on the exact same vehicle this evening. It can all be done "top side" with the proper extending tools and a long arm.

I am trying to help a buddy with his emissions issues..he says he had the egr replace just a few months ago...are we looking at a vacume leak...or another culpret? I am not familiar with Toyotas inparticular...if the egr has been replaced to no avail...should th evaulve to the left of it get replaced too?

that and or the egr solenoid. the valve itself never fixes it, for some reason they dont go bad, 85 percent chance its the egr solenoid and 15 percent its the back pressure valve

smell
sometimes smoke
muffler noise or hesitation rattle sound
engine light on troubleshooting code when check does po401 damage engine
I think also there exaust leak in muffler cause of smell can it trigger po401

start and run engine at idle air shold escape form filter in pic. check resistance of piece with engine off it shold be 33-39 ohms at 68 degrees then check for continuity between each pole and body of valve if there is replace it.

1996 Toyota Camry 200334 miles 2200 engine where is the EGR ? I have a code of P0401 Exhaust Gas Recirculation Flow Insufficient Detected. what do I do?

Check the vacuum diagram sticker on the hood..

There you can find it.

[quote:6bd421b200="jlbowers"]1996 Toyota Camry 200334 miles 2200 engine where is the EGR ? I have a code of P0401 Exhaust Gas Recirculation Flow Insufficient Detected. what do I do?[/quote:6bd421b200]

make sure the switch over valve is working before replacing egr