The dreaded and annoying P0401 code

So I’ll start off by saying I’ve searched far and wide for posts about the P0401 code. It’s been awhile since I’ve posted (had a previous account with my first Tacoma). Other posts have been helpful but I’m looking for a bit more specific help from any of you 2.7l wizards.

I bought a 2001 6 lug Tacoma with the 2.7l (211k miles) about a month ago for a price I couldn’t pass up. The catch was a CEL on and the SRS light on. I’m not too concerned about the SRS right now since I need to fix the CEL to pass smog here in California. I plugged my OBDII scanner into the truck and popped a P0402 - Excessive Exhaust Flow.

The truck came with a new EGR, new VSV, and new EGR temp sensor the previous owner bought so I threw them in. I did a Seafoam treatment while I was messing with stuff. Throwing the new parts on it fixed the P0402 but tripped a P0401....

I’ve tried my best to clean the EGR / TB ports and none seem to be clogged. I’ve checked the VSV (applying 12 volts) to verify it works; which it does. I’ve cleaned the EGR tube, changed the EGR modulator, changed the cracked or poor looking vacuum lines, I cleaned and reinstalled the old temp sensor and even removed the new EGR to make sure the port wasn’t clogged. All that done and the P0401 still comes back. I’ve driven at 50-55 MPH for 20 minutes a couple times hoping the ECU resets. Nothing. I checked vacuum at the EGR at operating temp. I apply vacuum and the truck doesn’t stall... weird. Also, when I pulled off the EGR Valve to clean it I verified the valve moved up and down.

I’m at a complete loss. Could the A/F sensor (upstream O2) throw the code? Or is there something simple I’m overlooking? Sorry for the long post. I figured maybe there was someone out there that needed some good toilet reading material.

 

Easy fix. Somehow people don’t know this. So first off locate your intake manifold, There will be 3 “L” shaped elbows with vacuum lines running off them into that little diaphragm piece that’s in the shape of a disk. You need to blow compressed air into the two or three metal elbows, they get clogged with carbon and gunk! I’d Suggest replacing that circular diaphragm also because the smallest crack in it will cause a check engine light. Super easy fix. If that is the reason for the check engine light it will turn off by itself with a little driving. Good luck!

 

My 96 3.4 Tacoma threw the P0401 code I changed the vcv and grommet replaced the egr problem solved. I would start there. Like everyone else says check vacuum lines as well