PO401 Defeated!! (1 Viewer)

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Bear80

Bear80

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Sep 23, 2004
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Well my 97 has been driving me crazy with the constant come and go of the PO401. First I tried switching the control for the EGR valve, nope. Also note there was absolutely no carbon in it nor the lines. So I guess it's my VSV control, and what a pain to get to. Could also be the sensor its self. Then I've heard the pesky PO401 will still come back some time down the road even after changing all of those parts.

The resistor replaces the input from the EGR gas temp sensor. Simply leave the temp sensor in the intake but unplug it and plug the resistor in. The sensor is located on the rear of the intake not far from the EGR modulator.

I used two female connectors taken from a toyota plug and soldered them on a 1k ohm, 5 watt resistor. Some heat shrink and your done. However I have noticed it will not kick the CEL OFF. I had to either re-set it will a scanner and then install the resistor or wait till the CEL went off by its self and then install.

NOTE I tried this only as a TEMP fix, but it's worked so well I may just leave it as is.

--UPDATE--, ecu looks for a 1k ohm range not a 1 ohm! simply follow the thread but with a 1k ohm resistor.
DSC00217.jpg
 
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I hear this has happened to other folks....I had the 401, I put in a new modulator. cel stayed off for a couple months, then I got a 402 (excessive flow iirc). I thought I had the 401 again, but Jim R. scanned me and it is a 402 now. He re-set me and the light has been off 4 days (whoopie!).

Will your fix work for a 402 as well as a 401? I hate having the light on for that, mostly cause it could mask another light. Although anything serious would blink....

Thanks for sharing your success.
 
The 401 and 402 come from the EGR gas temp sensor. So it fixes either one and how can it kick on the code if you have the computer fooled??

A month, HA try like 6 months now and still no CEL. I would not have made a post if I was not some what confident in my work. Trying to omit usless posting in the tech. :D
 
tarbe said:
I hear this has happened to other folks....I had the 401, I put in a new modulator. cel stayed off for a couple months, then I got a 402 (excessive flow iirc). I thought I had the 401 again, but Jim R. scanned me and it is a 402 now. He re-set me and the light has been off 4 days (whoopie!).

Will your fix work for a 402 as well as a 401? I hate having the light on for that, mostly cause it could mask another light. Although anything serious would blink....

Thanks for sharing your success.
Click to expand...


If you are getting a 402 make sure that the vacuum lines that go to the VSV aren't plugged. The plugging of these lines (especially the one that goes through the intake plenum) is what was causing my 402.
 
Bear do you have emissions inspections in your area?


The reason I ask is because you may not pass a visual with that gizmo sticking up like that.


Think stealth ;)
 
But if the sensor is not sending the correct signal it will trigger the light and you will flunk the test...
 
Bear80,

Why don't you just replace the VSV for EGR and be done with it?

-B-
 
B- he said his EGR was perfect.
 
I guess that's why the light won't go out......;)
 
concretejungle said:
B- he said his EGR was perfect.
Click to expand...

Not the word choice I'd use but yeah sure...perfect.

I got started with the resistor when I was bored in the garage and took a look at what I had around for resistors. But the only thing I've checked is the moudulator and the sensor, so the only thing left is the VSV. But like I said some have said even after all that the code comes back after a few years.
 
I had the the same P401 code and solved it by replacing the EGR Modulator which is the round shaped part in the upper left hand quadrant of your picture. The passages and filter were caked with carbon. I also had to replace my upper 02 sensor soon thereafter. That was 6 months ago and no codes popped up since.
 
landtank said:
Good fix Copperfield, what do you plan for an encore, a brick on the accelerator for a faulty Cruise control?
Click to expand...


Well if the dumbass who designed the cruise control system originally started out with a zip tie, a brick would definitely be an improvement...... The point is the LC EGR system was poorly designed and PRONE to early and frequent failure(just like the seatbelt retractors in my various Toyota pickups). I think Bear80 has a great alternative and am headed to Radio Shack.
 
I have been living with P401 code for a while also. Changed my EGR modulator and the P402 code showed up, plus my fuel economy went down about 1 to 1.5 mpg.

I put the old EGR modulator back on and the P401 code came back also. But at least my MPG went back also.

Probably get to the VSV this summer some time & see if this works for my truck.
 
Properly working egr lowers cylinder temps. Lower cylinder temps enable more advanced timing without knocking. More advanced timing enables better performance and fuel milage. The computer automates the above.

Correctly functioning egr is beneficial to your wallet, your seat of pants, and the atmosphere.
 
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