Check engine light in my 1997 4Runner 2.7L has been on a couple months and its the P0401 code. I replaced the vacuum modulator and the vacuum switching valve but the light remains on. I have zero drivability issues. Anyone have any suggestions? Thanks

 

Seafoam.

 

I had the same issue with my 2000 4runner 2.7. I couldn't figure it out for the life of me. New modulator, new vacuum switch, new egr valve, new temp sensor, cleaned the EGR pipe, but still had the code. Then I found a exhaust leak at the back of the manifold just before the upper exhuast pipe. It was small bit it was enough.

 

Thanks for the info

 

What sovled the P0401 in this instance?
I have the same issue, cleaned out the carbon and replaced a few vacuum lines but still have the fault. On a budget and need to get through state emissions test ASAP

 

Too bad the OP never posted his solution. Everyone should, for the benefit of those with the same symptom. I had this issue (P0401), and solved it by removing, cleaning, and re-installing the EGR temp sensor. After the first cleaning, the 0401 came back after 2 months, then I did a more thorough cleaning (scraping the black crude off with a knife). That did the trick. Next time, I'll just replace it.

 

I replaced the parts I mentioned in the op but they did not fix the problem. After a couple more weeks of problem free driving I opened the hood to have another look around because that light is annoying. That's when I finally spotted a cracked vacuum line. I guess the crack finally got big enough over a 3-4 month period to be seen. It was right on top of the motor staring at me when I opened the hood. It was the shortest vacuum line on the truck, only 2-3 inches long and it bends at almost a 90 degree angle. I ran to the parts store and they cut me a short piece for free. I took it home, got it worked back on the fittings and the light went away. Check your vacuum lines thoroughly.