I replaced my EGR valve and EGR modulator but I still get this code. Any ideas what might be causing it to recur. Thanks
EGR P0401 fault code keeps returning
- Thread starter Douglas Carter
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Have you made sure that every vacuum passage involved is clear and that the VSV is operating properly and all vacuum hoses are intact?
Check the vsv quick and easy
Follow the lead out from the vsv to where it plugs in and unplug it.
Now you need to jumper wires with alligator clips and clip them to the plug off the vsv u want the two leads with the yellow wires. You will see two yellow wires going into the plug. Now hook the other end of the wire onto batt one pos one and one onto the neg, doesn't matter which. You should here the switch click, now with it on still unplug the hose out egr and if I remember right you should not be able to blow thru it. Now unplug your leads from batt and see if you can now blow thru if all that work vsv is good. This way you won't have to try fish that switch out unless of course it not working
Follow the lead out from the vsv to where it plugs in and unplug it.
Now you need to jumper wires with alligator clips and clip them to the plug off the vsv u want the two leads with the yellow wires. You will see two yellow wires going into the plug. Now hook the other end of the wire onto batt one pos one and one onto the neg, doesn't matter which. You should here the switch click, now with it on still unplug the hose out egr and if I remember right you should not be able to blow thru it. Now unplug your leads from batt and see if you can now blow thru if all that work vsv is good. This way you won't have to try fish that switch out unless of course it not working
- Thread starter
- #5
Thanks for the tips. I'll keep everyone updated
This is a couple 1k miles of testing so I think it is worth saying. I did EVERYTHING to fix my egr code in my 97 LX. Cleaned all ports, swapped out all parts. Light still came on. Tried switching to super on a 1k mile round trip to Florida and bam light staid off. So I thought I solved the problem. Well at the time my wife and I were house shopping and on our first time out after the trip the light popped on again. House shopping for me means lugging the truck through a neighborhood at 15mph for 30 or so minutes to check out a few houses in that area. Then I remembered the light would always pop on when we use to do that before the trip.
So the next time we go house hunting and the light pops on I unscrewed the gas gap and there was TONS of pressure. The gas line vented for awhile with a lot of force. This pressure must not build up like this on the highway. Because I test it after say a 10 mile highway run. Pull the cap and nothing happens. 20-30 minutes lugging through a neighborhood and the gas line vents so hard my hair moves.
I did this many times as we house hunted and EVERY time the light would pop on just after going through a neighborhood. And every time I would unscrew the cap it would vent HARD.
Now that we have a house we don't drive all slow through neighborhoods like that anymore except on say Xmas to check out the lights. So what I would do when we were don't looking at the lights is I would hope out of the truck vent the gas cap and the light wouldn't come on.
Drive slow through neighborhood to drop kids off at play dates. Pop that gas cap off to release pressure and no light.
If I put 280 miles on the tank all highway there is 0 pressure.
20-30 minutes of idling and 15 mph driving and there is tons of pressure.
A charcoal canister is on my list but the light stays off if I vent it after those types of situations.
For giggle when your light turns on unscrew the gas cap and see what it does.
So the next time we go house hunting and the light pops on I unscrewed the gas gap and there was TONS of pressure. The gas line vented for awhile with a lot of force. This pressure must not build up like this on the highway. Because I test it after say a 10 mile highway run. Pull the cap and nothing happens. 20-30 minutes lugging through a neighborhood and the gas line vents so hard my hair moves.
I did this many times as we house hunted and EVERY time the light would pop on just after going through a neighborhood. And every time I would unscrew the cap it would vent HARD.
Now that we have a house we don't drive all slow through neighborhoods like that anymore except on say Xmas to check out the lights. So what I would do when we were don't looking at the lights is I would hope out of the truck vent the gas cap and the light wouldn't come on.
Drive slow through neighborhood to drop kids off at play dates. Pop that gas cap off to release pressure and no light.
If I put 280 miles on the tank all highway there is 0 pressure.
20-30 minutes of idling and 15 mph driving and there is tons of pressure.
A charcoal canister is on my list but the light stays off if I vent it after those types of situations.
For giggle when your light turns on unscrew the gas cap and see what it does.
To your point, gas caps fail over time also. A new gas cap is sometimes what's needed.
- Thread starter
- #8
I have two questions.
1. Where is the VSV located. Can I replace it without removing a bunch of other stuff.
2. In the attached photo, what is the hose with the arrow on the left (P/N?). This one has a crack in it at the base. Might that be a cause of my problems. Is the one on the right coming from the PCV?
Thanks
Doug C
1. Where is the VSV located. Can I replace it without removing a bunch of other stuff.
2. In the attached photo, what is the hose with the arrow on the left (P/N?). This one has a crack in it at the base. Might that be a cause of my problems. Is the one on the right coming from the PCV?
Thanks
Doug C
Your intake hose is completely shot. Wow.
Edited to add: The aftermarket plug wires are also a big "no go".
The condition of the PCV hose is also not a good thing. I'd replace it if I were you.
And yes, the one on the right is the PCV.
Ha, yeah looks like alot of air leak potential there! Start with the basics and get all that cracked rubber replaced.
Curious but how did you get a EGR Modulator? They have been discontinued. I have looked around and cannot find one.
- Joined
- Jul 20, 2004
- Threads
- 274
- Messages
- 23,204
- Location
- Chandler, AZ
- Website
- www.tontorecreationalliance.org
Easy deal, unplug the thermistor connection on the intake, connect a 4.7K ohm resistor. no more p0401 or P0402 codes.
- Thread starter
- #15
That takes care of the code... But what about the Modulator? Are you saying it's not needed? Maybe I should just do the desmog. I hate removing things designed to help the environment. And all that I have read says it does zero in return except free up Bay space. Really frustrating cause I wanted to finish my baseline and I cannot.
Kevin,
Will a 1/4 watt resistor do, or is something more heavy duty needed?
Will a 1/4 watt resistor do, or is something more heavy duty needed?
Rivman1243
SILVER Star
I had the same issue. 97 cruiser with P0401 code that wouldn't go away. I replaced the vacuum modulator, VSV, and confirmed my EGR valve was working properly. I replaced cracked crank case hose and PCV hose. No change and no other leaks.
I was also not able to pass smog in CA due to high HC at idle. Came to find that my Catalytic converters were shot, both of them. I had 277,000 miles on possibably original cats. I drove through some water while the cats were hot and damaged them. Once the cats were replaced, no more code. It seems that Toyota associated this code with the O2 sensor behind the cats as it was cycling too fast. Expensive fix, but problem solved. Hope this helps.
I was also not able to pass smog in CA due to high HC at idle. Came to find that my Catalytic converters were shot, both of them. I had 277,000 miles on possibably original cats. I drove through some water while the cats were hot and damaged them. Once the cats were replaced, no more code. It seems that Toyota associated this code with the O2 sensor behind the cats as it was cycling too fast. Expensive fix, but problem solved. Hope this helps.