P0401 : EGR Flow Insufficient on 1996 Toyota Corolla

Hi, I am getting the same code. Is it hard to replace the EGR Valve?

on what kind of car? A toyota?

yes, a 96 toyota corrola 1.6litre if I get one of the HAyes manuals -- will it show pictures of where it is and how to replace this device?

maybe, I'd recommend a subscription to http://www.alldata.com , close to the same price as the Haynes manual and the quality isn't even comparable, That's not a paid endorsement or anything just speaking from lots of experience

on EGR codes, we recommend replacing the EGR, vacuum modulator and VSV (if equipped) and cleaning out the carbon buildup to the intake from the EGR valve. if you want to test the EGR valve, just get a Mighty Vac, apply vaccuum and see if the car stumbles and/or dies when applied. Check the VSV, just put 12VDC to the VSV and blow through a hose. If you can blow through it-good. And when you take off the 12V, you shouldn't be able to blow anything through it. BUT EGR valves and VSV's DO intermittantly get stuck. So to be safe, we recommend repalceing all 3 and cleaning out the passageway.

thanks for the replies

keep us updated on how it turns out!

I am working on 97 Corolla right now and its getting P0401 code so i checked Solenoid VSV (it' GOOD), Checked EGR (its GOOD and cleaned it), Took out MODULATOR and cleaned all the ports (everything looked good) only thing i noticed is that port "P" on MODULATOR is a dead end i don't think it's clogged because i soaked it in brake cleaner and i used compressor to blow thru nothing worked. But the line that goes off Throttle Body "E" or maybe it's "P" and goes to "P" on VSV got vacuum when the car is running so i found that wired. Also port on Throttle Body "R" is not getting any vacuum or doesn't doesn't blow thru so it's like clogged or something tried to clean it by opening TB and spraying brake cleaner and then using Paper clip to push it in but no results. That "R" port goes from TB to MODULATOR "R" port. So i am a little confused because it seem like MODULATOR not getting any Vacuum since "P" on MODULATOR is closed shut and "R" port on TB is blocked. I don't think they both got so clogged up that i can't clean them out. This actually makes this car Federal or something because EGR is not activated ever. But i still get the P0401 code and i know the car is CA. So what you guys think of this deal? I also think it could be MAP sensor, because that's what Mitchell telling me to look for after i checked all those parts. Any ideas on this? I really need some input on this situation, i need to get this car SMOGED so i can sell it (already got deposit). Discover more Forum Engine Ignition coil I drew a diagram of EGR and VSV and EGR Vacuum Modulator since my scanner is not working and i can't upload the Vacuum diagram of EGR System. All of your input will be appreciated.

so does the car stall when vaccum is applied to the egr circuit?

Yes, car dies when i apply vacuum to EGR. I only applied vacuum to EGR diaphragm and not to Modulator. Do you think i should apply vacuum to EGR Modulator and see what happens. Which port i should apply it to? port "R" or "P"???

I think you change the vsv first!

I have already changed VSV and i know both are good. I also got another 97 Corolla and i used VSV from that car to see if there any difference but none. Well i just figured out the problem it was EGR Modulator, i took it off the good car that got NO CE light and it passed smog. Put it on the car that keep throwing P0401 code and drove it for 45 miles. No codes came on. Used my scanner to see if all the monitors were ready for smog. Suprizingly everything was ready except Catalytic Converter, but it's only one thing so i knew it should be OK with OBDII reader from smog machine. Took it to SMOG check 20 min later i got my SMOG papers and it all passed. So it end up being EGR Modulator after all. Allied Auto Parts sell them for $92 but at Rockauto.com they have them for $47.79, best price online: http://www.rockauto.com/catalog/x,carco ... rtGroup,19 Thanks for your help.

You're lucky to have another car lying around to yank parts from!

Recently went through this problem on three different Toyota products (97 Lexus LX-450, 97 camry, and a 96 Land Cruiser). In each case, the problem was the EGR modulator valve (labeled on top with letters P,Q,R) on top. The easy check for this valve is to disconnect the 1/4" hose from the bottom of this sensor. If you can't hold a vacuum on this port to the valve (it is to a sealed diaphram inside the valve), the valve is bad. At our shop, we had several of these lying around from different Toyotas, and about 1/2 were bad. If you had saved your old valve, I'll bet you would have found that it failed this simple test.

nice tip!

I read the history of posts and my problem seems similar. I have the P0401 CEL code. If I have Advanced Auto reset it, I can drive a couple of hours to a couple of days before it triggers again. My car doesn't seem to be running badly, but I want to get rid of the check engine light I got a Chilton manual from the library and followed the instructions: 1. I checked the EGR valve by applying vacuum to the EGR valve at port Q - the diaphragm while the engine was idling. The vaccum remains steady. The engine not only runs poorly... it stalls. I think this causes excessive EGR flow at idle causing the engine to stall (IS this correct ) 2. I checked the EGR modulator by disconnecting all the hoses, then blowing air into port Q... air comes out ports P and R. The manual says to block ports P&R and to verify the air flows out through the air filter and out from under the modulator air filter cap. If this happens it is very hard to sense the air flow. I can't tell if slight to no air flow is expected or indicates a problem. However, I checked the filter. it's dirty, but I can't seem to blow it clean and I can't find replacement parts for the filter anywhere... it's hard to beleive you would replace the modulator for lack of a replacement filter. 3. I had my wife rev the engine to 2500 rpm, so that I could blow in port Q again and verify resistance to the flow. I didn't get that far.. it seemed like I had air blowing from ports P and R even though port Q was also disconnected. It seems like that pressurized air could only come through the seal that seperates Chamber A (the pressure from the exhaust pressure chamber) and the rest of the valve. So I thought I must have a leak in that seal. Then I noted the previous posts which suggested drawing a vacuum on the bottom chamber of the modulator. I did it and the vacuum held. Any thoughts?

I just had one of the worst experiences with a 97 corolla 1.8 auto. My girlfriends car. I used a scan tool and got a code for EGR insufficient flow or P0401. I REPLACE THE EGR VALVE AND GASKET (EASY) cleared the code and 40 miles later, the CEL was back. I then proceeded to research. Others had said to replace the vacuum solenoid thingy (easy), so i did with the same result. Now I'm pissed. So I continue my research and discover the culprit... The VSV or vacuum switch valve!!! I used info from this site to fix the problem. I pulled the vsv and applied 12v to the terminal. You should be able to blow through the plastic port... Nothing happened. So I proceeded to bang it around gently with a hammer on the side and magically the valve reopened and began to work. I was able to blow through it when voltage was supplied!!! I just completed the reinstall and cleared the code. Lets hope it works... Otherwise I will be force to buy one... It also just so happens this part is rather hard to come buy....and expensive anywhere from $300 to as low as $85 on some Toyota Wholesalers website. For my application part # 90910-12141. I will keep my finger crossed that this works at least for the upcoming SMOG TEST!!! Damn California!!! So beware of the dreaded EGR Code P0401 its not a simple fix for the shadetree/backyard mechanic. Do your reaserch before spending $170 for an EGR valve and $50 for the solenoid. Check the VSV!!! BTW Said corolla has roughly 190k... Good car!

I had a P0401 for the longest time. My annual inspection was coming up and I had to get that CE light off. I read all the entries on this forum and tried checking the EGR valve and the modulator (they were easy to get at). The recommendations that seem the most was to replace the VSV. I took a chance and went for that component. It took some effort to get it out. Had to work thru the right front wheel opening to reach it. Everything was done more by feel than sight. You had to reach in and feel the bolt to get a socket on it (lost the bolt taking the socket off it, just vanished). Anyway drove around abit and the CE light went off. Took it for the inspection and passed. The light is still off and the OBD tester shows no codes. Thank you to all who participate in this forum. Your knowledge and help is greatly appreciated. PS-the VSV at Toyota cost 75. tax included.

I posted ^ up there somewhere ^... The V.S.V. was the problem. CE light has been off for a week now... Just smogged and it passed!!! YAY!!! CHECK THE V.S.V. BEFORE YOU BUY ANY PARTS RELATED TO THIS CODE!!! THE V.S.V. IS THE ONLY PART THAT HAS SUPPLIED POWER AND WHEN IT IS NOT WORKING THE P0401 CODE WILL COME UP!!!