I have searched and searched for a solution for the PO401 and this is what I've done... (1 Viewer)

[BullElk]

Per searched threads on PO401...

I have tested EGR valve....GOOD
I have tested EGR modulator....GOOD
I have tested VSV switch--- continuity between prongs... 32-34ish ohms, tested prong and metal
casing...O ohms, without voltage applied...CAN blow air thru switch, with voltage applied...definitely
cannot blow air thru switch.
I have heat wrap protecting wiring harness
I have oil catch can on PCV hose and new PCV valve

Still get 401 code.

What have I not checked?

Thanks

 

[Tredwards]

Check your throttle body to make sure the 90 deg metal piece where the vaccuum lines attach to there are not plugged. If you can blow air then I would assume the upper intake penum pass through is open.

 

[BullElk]

"90 degree metal piece"....do you mean that attaches to other valve cover hose? I can blow air thru that.

 

[Tredwards]

On the throttle body if I remember er there are 3 metal Elbows. On the 1fzfe. 2 come from the egr and I forget where the other comes from. The 2 coming from my egr were fully clogged with carbon deposits. I had to spend roughly 1 hr with a small pick and throttle body cleaner to get cleaned out

 

[Tredwards]

These are for the small vaccuum lines. Not the pcv system.

 

[BullElk]

Oh yea. Gotcha. I did try blowing on them. Air seemed to move some but I will get some cleaner in there anyway.

 

[wearsabrowncoat]

Does your EGR temp sensor look like this?

 

[BullElk]

I pulled that and checked that as well a week or so ago. Yes, it did look like that but I cleaned it up best I could. It looks much better now but I guess it still could be the culprit. What did you do with yours...clean or replace? Thanks

 

[wearsabrowncoat]

Cleaned it up with a soft metal brush.

 

[Phildoh]

You said egr valve good, good airflow, cleaned out carbon build-up? And does the code keep popping up after clearing it? And it's stored as a "hard" code (major malfunction), have you cleared it, start the engine briefly, turn off, disconnect battery for 10min, then connect and retry? I've had this with a couple other Toyota models, a Tacoma and a Camry, has to disconnect the batt after clearing it, then it stayed off. I'll ask my smog guy tomorrow if you're still FUBAR.

 

[BullElk]

I tested the egr valve by creating a vacuum on one side then pinching hose on another....and engine stalled as it is supposed to. So I guess it's good. I have not taken it off to clean, however.

I have disconnected just the positive terminal for about 20 seconds. It still comes back on no matter what. I will disconnect again as you suggest.

 

[handsomebob]

Are the egr vacuum lines hooked up correctly? Might want to check those out.

 

[Phildoh]

If you've disconnected already, then don't bother doing it again. I'll ask my smog guy tomorrow for ya

 

[GW Nugget]

I didn't see mention of checking the modulator. I'm chasing the same thing. I'm tired of throwing money at that silly light.

 

[Qball]

Just change the modulator, they are cheap(at least the eBay ones), that's what fixed my p401 and my old modulator tested fine.

Also I assume you changed all the vacuum hoses. Also take a long wire and clean out the EGR passage in the intake from your egr temp sensor port.