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New here, I'm an auto tech at tcm automotive in TX, however I've been fighting a p401 code. I have a 1996 camry with 364,000 and the car runs great but this code will make it so I cannot register it making it useless, even though it drives great. So I really want to take care of this.
So far the egr vsv has been replaced and wiring checked good, using a snap on scanner turning it on and off. Replaced Egr modulator. Tested the egr itself and passages to see if blockage, which there is not and the egr is functioning properly. Now the evap purge solenoid ground wire is flickering when turned on via scanner access. Which is direct to the ecm. So I changed the ecm and it is still flickering ground on the vsv. And you can hear the solenoid clicking constantly from turning off and on by the flickering ground.
The power wire is reading solid no issues there. The wiring looks fine to the ecm as well. This is making me pull my hair out. I dont know what else to try. They no longer make new ECM for this year so it is remanufactured. But the possibility of two bad ECM's is very small. And from what I researched. The Ecm gets its ground from an internal ground INSIDE the ECM itself. So that ground is faulty inside possibly in two ecms?
As well I even tried to just bypass the evap purge solenoid allowing full flow at all times (as the code is insufficient flow). And even then the code came back. So I dont know what else to try. I dont have much experience with these elaborate emission systems on toyota, Really appreciate any help guys.
This is the EGR vsv (yellow arrow points to part of it) in which I replaced with the OEM vsv and I tested the circuits with no problems occurring.
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This is the evap purge solenoid next to the canister. That yellow black wire (hard to see) next to the pink crimp, is the wire that is flickering ground.
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The yellow and black wire pictured here on the left pigtail is the ground wire to the evap purge solenoid that is flickering ground.
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'00 4 Cyl. Auto Camry LE
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Does a resistance check on the EVAP purge solenoid ground wire from connector <-> to ECM reveal anything?

What about a continuity test from connector -> ground, or ECM connector -> ground?

Have you re-verified vacuum hose fitment / integrity from the Intake manifold to the EGR VSV? And (other) hoses / ports on the Intake manifold?

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If here, I would start w/ the basics: primary Battery inspection: terminals, cabling, cleaning ground points to engine & frame, voltage (drop) check(s) @ ECM fuse / passenger cabin fuse block. Verifying the ground strap(s) on the lower intake manifold are secure and clean. Any line resistance or continuity on the EVAP purge solenoid trigger line needs to be further investigated. ... Hope this helps.
 

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I don't think the evap purge solenoid has much or anything at all to do with the EGR system. The EGR system is the EGR valve, the modulaor, the VSV for EGR, metal pipe, all related hoses, gaskets, and the ECM. The Toyota repair manual doesn't even mention the evap purge valve in the EGR testing section. Can you post a photo of the VSV for EGR that you replaced? I ask, because in the explanation of the first photo you posted, you said "This is the EGR vsv in which I replaced with the OEM vsv and I tested the circuits with no problems occurring", but I don't see it in the photo, and in fact, it wouldn't show since it is located down on the side of the engine block on the firewall side. I want to make sure we're talking about the same thing. This VSV for EGR is often the culprit. Have you checked the metal pipe for blockage (at both ends)? Check ALL the hoses for blockage or leakage. Check all ports for blockage. All the hoses are 3.5mm id except for the one hose that fits on the bottom of the EGR (get that hose from Toyota). Check that the tiny ports in the throttle body that connect to EGR hoses are not blocked. It's got to be one or more of the things I mentioned.
 

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First thing I'd do is remove the butt splices and properly solder and heatshrink those connections. Butt connectors are notoriously unreliable.
 

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Discussion Starter #5
Does a resistance check on the EVAP purge solenoid ground wire from connector <-> to ECM reveal anything?

What about a continuity test from connector -> ground, or ECM connector -> ground?

Have you re-verified vacuum hose fitment / integrity from the Intake manifold to the EGR VSV? And (other) hoses / ports on the Intake manifold?

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If here, I would start w/ the basics: primary Battery inspection: terminals, cabling, cleaning ground points to engine & frame, voltage (drop) check(s) @ ECM fuse / passenger cabin fuse block. Verifying the ground strap(s) on the lower intake manifold are secure and clean. Any line resistance or continuity on the EVAP purge solenoid trigger line needs to be further investigated. ... Hope this helps.
Resistance and continuity test good. No issues with the wiring from what I've tested. The hoses are fitted tight with new clamps in which I installed. The hose fittings all have been secured firmly. I have also removed the EGR to manually test it and check the ports and find no failure within the EGR. I have also not seen any ground on the intake whatsoever. However that may have been possibly moved by the previous owner with the vsv. All the rest of the wiring tests good throughout the fuses and junction box as well. I've put as much time into this as I possibly can and have found no leads on this. I have had over 40hrs under the hood in the last week and cannot find anything.
I don't think the evap purge solenoid has much or anything at all to do with the EGR system. The EGR system is the EGR valve, the modulaor, the VSV for EGR, metal pipe, all related hoses, gaskets, and the ECM. The Toyota repair manual doesn't even mention the evap purge valve in the EGR testing section. Can you post a photo of the VSV for EGR that you replaced? I ask, because in the explanation of the first photo you posted, you said "This is the EGR vsv in which I replaced with the OEM vsv and I tested the circuits with no problems occurring", but I don't see it in the photo, and in fact, it wouldn't show since it is located down on the side of the engine block on the firewall side. I want to make sure we're talking about the same thing. This VSV for EGR is often the culprit. Have you checked the metal pipe for blockage (at both ends)? Check ALL the hoses for blockage or leakage. Check all ports for blockage. All the hoses are 3.5mm id except for the one hose that fits on the bottom of the EGR (get that hose from Toyota). Check that the tiny ports in the throttle body that connect to EGR hoses are not blocked. It's got to be one or more of the things I mentioned.
Yes, so I've tested the EGR vsv as well as its wiring, as well as its function under driving conditions and find no problems (after VSV replacement with a toyota OEM vsv). It is the picture of the top of the engine with the wire running to the passenger side of the bay. I would assume the previous owner moved the VSV from under the intake. Which is fine as I have replaced the hoses to rule out possible hose collapsing due to age.
  1. So the evap purge solenoid comes into affect due to the vacuum it opens to the throttle body, in which feeds the EGR system in itself. So that's when it comes into play. Either way there is an issue with it. As the ground is intermittent. Just flickering. So it's very peculiar.
  2. First thing I'd do is remove the butt splices and properly solder and heatshrink those connections. Butt connectors are notoriously unreliable.
    Interesting! I've used them for years in the auto industry in several shops and never had any issues. All the other techs around me find them reliable as well.
 

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Yes, so I've tested the EGR vsv as well as its wiring, as well as its function under driving conditions and find no problems (after VSV replacement with a toyota OEM vsv). It is the picture of the top of the engine with the wire running to the passenger side of the bay. I would assume the previous owner moved the VSV from under the intake. Which is fine as I have replaced the hoses to rule out possible hose collapsing due to age.
  1. So the evap purge solenoid comes into affect due to the vacuum it opens to the throttle body, in which feeds the EGR system in itself. So that's when it comes into play. Either way there is an issue with it. As the ground is intermittent. Just flickering. So it's very peculiar.

  2. Interesting! I've used them for years in the auto industry in several shops and never had any issues. All the other techs around me find them reliable as well.
I see it; it's partially hidden behind the diagnostic port, and I was wondering if that was it. I edited the photo with a yellow arrow pointing to it, so others can see what you mean. Yes, it's relocated, which I have also done on a couple of different Camry cars. I relocated one to a threaded hole on the intake manifold and another to a brake line bracket bolt on the firewall. There should be a sticker on the underside of the hood showing the proper routing of all the hoses, so make sure the hoses are routed correctly. The only concern I have is the long distance the relocated VSV is requiring of the two hoses. Maybe that doesn't matter. Also, the one hose that goes over the spark plug wires looks too big. It should be 3.5 mm inside diameter, and I'm not sure if that replacement hose you have is quite a bit bigger than that and if that causes an issue with the pressure in the hoses not being high enough. Maybe the inside diameter is fine and it's just got a thick outside diameter which is throwing me off (or perhaps the photo makes it look too big when it isn't).

I agree with @insightbrewery about those butt splices. If you verified the ones for the VSV for EGR are indeed conducting the signal, then I guess that's OK and is not the cause of the issue. What about getting the correct pigtail/connector to snap into the VSV instead of just the wires plugged in there? As you said, it's responding electrically, so I guess its OK, but I personally would use the correct snap-in pigtail connector and solder the wires. Even though the VSV is responding electrically, did you verify that air flows through the VSV at the appropriate time and that air does not go through when appropriate?

I understand your point about the evap purge solenoid valve, but again, the Toyota manual does not associate it with the EGR when doing diagnostic testing. Maybe you're right, but according to the manual it's not an issue of testing for the EGR. Nothing wrong, of course, with making sure it is working correctly, and if you are right, and fixing that does fix the EGR issue, then I would definitely want to know about that so we both can help others in the future. The Toyota manual is not always 100% correct about everything and if the evap solenoid is indeed a factor, then I want to know about that for the same reason.
 

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P0401 "insufficient flow" really means no change is detected after activating the VSV. I actually think you are more knowledgeable than me, but you probably have not read the articles from Motor magazine.

In https://www.toyotanation.com/threads/p0401-and-p0446-story-time-with-a-happy-ending.1668246/post-14158977, I listed my general suggestions. In the third link in that post, there is a section on "Diagnosis" with links to videos on Youtube, and articles from Motor magazine. There is a section on "Discussions", and someone did change his ECU, but I'd think that's the exception.

There are only 3 EGR parts. The EGR Valve is the most expensive and least likely to require replacement, and can be fairly definitely tested. You can test the other 2 parts, but they are not as definite (my Vacuum Modulator seemly tested fine, VSV may be sticky but test OK). I'd just replace the other 2 one by one (I got Dorman 911-609 and Aisin VST006).
 

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There is a section on "Discussions", and someone did change his ECU, but I'd think that's the exception.
I once had to replace the ECU on a '97 Camry to fix the P0401. I don't think the ECU was the original cause of the P0401, but in testing I mistakenly tested the signal wire connector that goes from the ECU to the VSV for EGR for resistance, which fried that one part (capacitor) of the computer. Got a cheap replacement ECU from the junkyard which solved the problem after also replacing all the hoses, gaskets, EGR valve and modulator. Ever since then I have made sure never to incorrectly test any wire that comes from the ECU. Won't make that mistake again.
 

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I see it; it's partially hidden behind the diagnostic port, and I was wondering if that was it. I edited the photo with a yellow arrow pointing to it, so others can see what you mean. Yes, it's relocated, which I have also done on a couple of different Camry cars. I relocated one to a threaded hole on the intake manifold and another to a brake line bracket bolt on the firewall. There should be a sticker on the underside of the hood showing the proper routing of all the hoses, so make sure the hoses are routed correctly. The only concern I have is the long distance the relocated VSV is requiring of the two hoses. Maybe that doesn't matter. Also, the one hose that goes over the spark plug wires looks too big. It should be 3.5 mm inside diameter, and I'm not sure if that replacement hose you have is quite a bit bigger than that and if that causes an issue with the pressure in the hoses not being high enough. Maybe the inside diameter is fine and it's just got a thick outside diameter which is throwing me off (or perhaps the photo makes it look too big when it isn't).

I agree with @insightbrewery about those butt splices. If you verified the ones for the VSV for EGR are indeed conducting the signal, then I guess that's OK and is not the cause of the issue. What about getting the correct pigtail/connector to snap into the VSV instead of just the wires plugged in there? As you said, it's responding electrically, so I guess its OK, but I personally would use the correct snap-in pigtail connector and solder the wires. Even though the VSV is responding electrically, did you verify that air flows through the VSV at the appropriate time and that air does not go through when appropriate?

I understand your point about the evap purge solenoid valve, but again, the Toyota manual does not associate it with the EGR when doing diagnostic testing. Maybe you're right, but according to the manual it's not an issue of testing for the EGR. Nothing wrong, of course, with making sure it is working correctly, and if you are right, and fixing that does fix the EGR issue, then I would definitely want to know about that so we both can help others in the future. The Toyota manual is not always 100% correct about everything and if the evap solenoid is indeed a factor, then I want to know about that for the same reason.
Yeah that tubing is a little long but it's right off our reel so it's great tubing. I wouldn't thing the length would affect the path of air, unless being pinched.
I didnt get the connector for the EGR vsv simply due to the fact that I've put over $800 into the car and its getting to be not worth it. As the car is really just a commuter. Doesnt even have a drivers side door panel on it.
That's interesting about it not mentioning it in the path of the EGR VSV. It was only a concern of mine due to the fact that there was very little vacuum on the two hoses out of the throttle body. And then I discovered the flickering ground. Other than that I really don't know what else could not be functioning correctly. The EGR VSV is functioning properly on the car and standalone test. No problem with the circuits there.
HOWEVER, before replacing the EGR VSV I had to replace all junction box fuses (under the hood not the drivers side box) due to slight corrosion, which was causing a flickering ground in the EGR VSV. And once I replaced the fuses it cleared up that issue with the EGR VSV. I tested the driver side junction box and everything seems to be in order, fuses in great condition, no loose wires or anything.
P0401 "insufficient flow" really means no change is detected after activating the VSV. I actually think you are more knowledgeable than me, but you probably have not read the articles from Motor magazine.

In https://www.toyotanation.com/threads/p0401-and-p0446-story-time-with-a-happy-ending.1668246/post-14158977, I listed my general suggestions. In the third link in that post, there is a section on "Diagnosis" with links to videos on Youtube, and articles from Motor magazine. There is a section on "Discussions", and someone did change his ECU, but I'd think that's the exception.

There are only 3 EGR parts. The EGR Valve is the most expensive and least likely to require replacement, and can be fairly definitely tested. You can test the other 2 parts, but they are not as definite (my Vacuum Modulator seemly tested fine, VSV may be sticky but test OK). I'd just replace the other 2 one by one (I got Dorman 911-609 and Aisin VST006).
Ahhh, well I dont know about being more knowledgeable. However I have tested the EGR valve itself and its functioning properly as well as the intake ports being clear. I replaced the VSV modulator, as well as the EGR VSV. So I have replaced the major portions of the EGR system and tested the EGR itself, which is a fairly mechanical part with low failure rate.
I once had to replace the ECU on a '97 Camry to fix the P0401. I don't think the ECU was the original cause of the P0401, but in testing I mistakenly tested the signal wire connector that goes from the ECU to the VSV for EGR for resistance, which fried that one part (capacitor) of the computer. Got a cheap replacement ECU from the junkyard which solved the problem after also replacing all the hoses, gaskets, EGR valve and modulator. Ever since then I have made sure never to incorrectly test any wire that comes from the ECU. Won't make that mistake again.
That's quite interesting that testing it blew the capacitor in the ecu. Now from diagrams I viewed via alldata, the current ran directly from the ecm to the vsv. So that's quite confusing to say the least. I can grab the diagram sometime tomorrow for reference.
 

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EVAP has nothing to do with EGR, so forget about that if you're dealing with an EGR code.

If you have a tool that has bi-directional controls and you can open the EGR VSV with it on demand, put in a vacuum gauge via a T into the line going back from VSV to modulator and see if it's building vacuum when actuated. The engine should run rough with EGR open at idle, as normally it's only supposed to open above 2k rpm.

Do you have the vacuum hoses hooked up correctly to the VSV? If not, you will get CEL. I may have done that myself back in the day...

There should be a ground wire hooked up to the intake manifold in the back. It's a little hard to see, but should be there. There are, of course, multiple grounds to the engine, but that doesn't mean it'll run better with some of them disconnected.
 

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EVAP has nothing to do with EGR, so forget about that if you're dealing with an EGR code.
Do you have the vacuum hoses hooked up correctly to the VSV?
YES!
 
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