(fixed) 97 toy tacoma 2.4L p0401

God bless you my brothers and sisters.
I have this 97 tacoma with a p0401 i apply vacuum to the egr truck stalls so egr is good. I also applied vacuum to the vsv valve and air was leaking slowly so i replaced it. The next day light back on same code this time i took the intake off cleaned all ports dirty but not plugged. At this time i also put a new vacuum modulator. The next day again light back on same code don't know what is next please help.
Thank you all for your help God bless.

Not familiar with Tacomas, but can you command the egr open with your scan tool to see the ecu has control? Is there a good vacuum to the control valve?


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Just thinking more about it, I'd also look for another vacuum device that isn't monitored leaking such as a throttle nudger so the egr valve has vacuum, but not enough. Also check for the vacuum supply ports are really clear.


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Hey Gilbert! I believe these systems use a backpressure transducer on the vacuum feed to the EGR? If so, they fail all the time. Let me know if it's got one, and I can detail how to test it. Really goofy system. :silly:

God bless you my brother's and sister's.
Thank you Matt for your help today I tried a different scanner and I was able to activate the vsv valve. This means that the PCM driver are good. The R line does have good vacuum at the throttle body I also looked for leaks and found none. I did find a dirty PVC if that makes a difference.

God bless you my brother's and sister's.
Hey Tyler thank you for your help I just put a diagram of the EGR system hope this help.

I'm following Tyler. I've never seen one.


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Sorry gilbert, I hadn't seen that you've replaced the vacuum transducer already, my bad. :blush:

With the VSV activated, do you get any vacuum at the EGR valve? These use some kind of goofy restrictor in the hose, so it won't be manifold vacuum. Around 8" would be good.

God bless you my brother's and sister's.
Hey brother i checked the egr valve for vacuum and it doesn't get any at any time. I checked the valve for vacuum at the Q line and activated the vsv valve and nothing. I T'ed from the Q and the vsv valve and activated the valve and nothing. Then straight too the egr valve and nothing the only line that has any vacuum is the R line.

It's not the check valve stuck is it? Or is the P line on the filter side of the throttle plate. Sorry, I've only got the diagram to go by.


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God bless you my brother's and sister's.
Sorry I have not mentioned that it is a manual transmission no check valve. What if I T off the R line will that work?

You may need to raise the engine speed while you activate the VSV, because of the way the vacuum transducer works. It gets exhaust pressure on the bottom, which moves a diaphragm and controls vacuum to the EGR. If there's not enough backpressure, then it won't flow vacuum.

Speaking of, another place to check is the hose coming off the exhaust, to the vacuum transducer. I've frequently seen carbon buildup in the pipe going to the vacuum transducer, which causes the transducer to never open. You can test for this by pulling the exhaust hose off the transducer and starting the engine, looking for exhaust flow.

God bless you my brother's and sister's.
Thank you brother I'll check on that and keep you posted.

God bless you my brothers and sisters.
The fix for this was blowing air through the p port on the throttle body. I had cleanded it with T/B cleaner until fluid came so i thought it was clean. I even poked it with a strand from a broom and it went through. That wasn't good enough to get enough vaccum so i blew it out with air and that took care of that. I drove the truck for three days and no check engine light thank you all for your help.

Nice! Good eye finding that plugged port, sir.