Lexus Es 300 Egr Insufficient Flow

Getting a check engine light with a P0401 code on the Es 300 it’s not unusual. I had this code come up on my 1994 Es300 few weeks back. Scanner shows P0401 Egr Insufficient Flow. While some people pointed the finger to Egr itself, i decided to search the other (easier) options first, starting with the Modulator. It turns out most of the times is the modulator that goes and that was my problem too. Modulator is shown with red arrow in the picture below and the Egr with the green one.

Taking the modulator out is easy, disconnect vacuum hoses attached to it, open the clips and pull it up.

Once out, you need to apply vacuum at the bottom pipe, just use your mouth and suck on it. It should hold vacuum and no air should get through it. If you get air coming through  it’s not good, time for a new one. I got a used one from a scrapyard for $40, a new one it’s about $100.

Now, if the modulator is holding vacuum then you have another problem somewhere, vacuum lines clogged or losing vacuum, stuck Egr, etc.. but it’s a good bet that the modulator goes first.

Comments (1)


  1. Kelly K says:

    The top part of my EGR modulator (the red arrow) broke off so the part that goes into the little vacuum tube is still in place. I can pull it out with pliers, but my question is do I have to but the entire assembly because the hoses broke off or can I just get that modulator cap thing?

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