I forgot to mention I have tried all of the drive cycles and have put over 500 miles since all of the repairs.. the vsv and modulator has been changed 2 times each. Genuine toyota parts each time. The cel refuses to leave me alone

 

make sure you get voltage on the rerouted hot wire to VSV and make sure the ground is good. ECU actuates things by switching ground side, not the hot side.

good article on troubleshooting EGR on Toyotas:
http://www.motor.com/magazine/pdfs/082009_04.pdf
http://www.motor.com/magazine/pdfs/092009_04.pdf
http://www.motor.com/magazine/pdfs/102009_04.pdf

as per FSM here are potential problem areas related to P0401:

P0401 = Exhaust Gas Recirculation Flow Insufficient Detected

detection condition:
After engine is warmed up, intake manifold absolute pressure is larger than value calculated by ECM while EGR system is ON (2 trip detection logic)

trouble area:
Vacuum or EGR hose disconnected
Open or short in VSV circuit for EGR
VSV for EGR
EGR vacuum modulator
EGR valve stuck closed
Manifold absolute pressure sensor
ECM

EGR gets cut off (VSV actuated) by ECU when following conditions are met:
Before the engine is warmed up.
During deceleration (throttle valve closed).
Light engine load (amount of intake air very small).
Engine idling.
Engine speed over 4,400 rpm.
High engine load (amount of intake air very large).

Assuming all the parts are good, then the problem must be related to either wiring harness or vacuum hoses.

Have you double-checked your splices and verified there is voltage on your wires when ECU tries to cut off EGR (by actuating the VSV)?

Have you checked the thick hose connecting side of EGR valve to bottom of modulator?

Hope it helps anything.

 

So when you pulled 3-5 in/Hg of vacuum on the EGR valve, the engine ran rough or stall? If this is the case then check the vacuum provided by the modulator to the EGR valve.

You can jumper TE1 and E1 in the diagnostic connection in the engine bay, passenger side. The engine should be at operating temperature. The vacuum reading should be the same on both ends of the hose going from the modulator to the EGR valve. See if there's 3-5 in/Hg at 2500 rpms.

Also, there are two hoses going from the throttle body to the modulator. If the two modulator ports on the throttle body are plugged that can be a problem too. So check those and make sure they're clear.

 

Well this morning I have confirmed the following:
On the p port I have 20 tp 22 in of vac at 3k rpm.
I have checked to verify that the egr kills the engine at 4 to 5 in of vac
The r port flucuates withthe engine rpm
I have battery voltage on one terminal at the vsv and at engine temp 0f 187 there is a ground on the other
when I check the vac on the q port at the modulator I get no more than 10 in of vac to the vsv
I jumpered te1 and e1 and I have 3 to 5 in of vac at the egr
I have double checked vac line routing
I did not splice the vsv harness just rerouted it
Large hose from modulator to egr is ckear and vac checked to make sure it wasnt leaking
When should ther be a ground on the vsv to signal it closed?

The replies to my post have been most helpful so far

 

MAP Sensor

Locate the MAP Sensor:



Disconnect the MAP Sensor connector and spray some electrical contact cleaner on both ends ... Let dry for a minute and reconnect.

... Just to make sure you don't have a bad electrical connection.
Get the plastic safe version of the contact cleaner.

 

Latest update: I have checked and double checked all electrical connections, cleaned them and have went through all the diagnostics again. I am pretty much resolved to the fact that there is a possibility the the cars ecu has gone stupid. My extensive trouble shooting and parts purchase and lack of finding a solution leads me to believe that this is the final piece of the puzzle.
I will be searching ebay and local salvage yards after I remove tge ecu and obtsining the numberd from it.
I will post again on my results.
Thanks to everyone and your knowledge had been most helpful

 

I can't find the information I was looking for, but I pretty sure the ECU uses the MAP sensor to detect when the EGR is operating. The MAF sensor is what the ECU uses for fuel control, and the MAP is only there for testing the EGR. See if the port in the intake manifold is plugged up where the vacuum hose for the MAP sensor connects. Check the hose and the end of the nipple in the MAP sensor.
You have ruled out most everything it could be. I highly doubt the ECU is faulty.
Don't lambast me, but are you SURE you are getting a P0401? Try another scanner, because I have personally seen some that spit out the wrong code in generic mode, but when you go to vehicle specific mode, you get the correct code.

 

there is no MAF on gen4 5s-fe, only MAP and IAT. he also stated the MAP and hose to it were both replaced ... I agree that the problem might be either the ECU (internal circuitry bad) or the wiring to it regarding the EGR circuits.

do you have any OTHER codes than the P0401? any pending ones?

 

Latest update: checking and rechecking. Since the vsv works off of the ground circuit, I found that the ecu was providing a constant ground to the vsv causing the egr to work constantly therefore the map srnsor couldnt see a change in pressure. Since the map sensor tells the ecu to turn on or off the vsv and there wss a constant ground I determined there must be a internal problem with the ecu. A trip to my locsl salvage yard and 50 buck later, and 30 minutes to change the ecu....I am pleased to announce that the p0401 pending and cel has vanished!!!
I am now in the process of completing the drive cycles and then a trip to the inspection station
I know that thid is a vety rare situation and I highly recommend that anyone with the p0401 code go through the troubleshooting procedures before changing the ecu. This took a lot of reading and an extreme checking and rechecking to chase this down.
It is apparent that I have purchased parts that I do not need but I will put the spares on the self should I ever need them.

I would like to thank all of the individuals that contributed to this forum thread and your input to this situation is extremely appreciated.

Happy motoring to all!!

 

if VSV was constantly actuated (grounded) by ECU then the EGR was cut off completely at all times (no flow at all), that explains the insufficient EGR flow code

yeah, THE ECU is the last piece of this puzzle, glad you solved the problem by swapping it out! grats!

 

Thank you fenixus for the correction. In my continuing quest to complete the drive cycle I found a very good toyota tsb eg003-02 that tells how to complete the drive cycle for a particular reset hooe this helps......now on to the problems with my 98 corolla....another post.

 

if you have OBD2 scanner, then check the Readiness Monitors (o2, catalyst, misfire, EGR, EVAP, etc.) , most likely the EGR test is already completed if there is no pending code for it :thumbsup:

 

Here's some more information that you might find useful in future repairs.

https://docs.google.com/folderview?...?id=0B51-74tGswAXYTIzNzY0OTQtNTIyMS00OTRjLWI1MjktMDYzNzUwYWNjZTll&usp=drive_web