Po401- Aahhh!!!! (1 Viewer)

[jerseyfzj80]

SO I hate my stupid check eng light, PO401 New EGR Valve, New Modulator, New VSV, Cleaned temp sensor (did not check) Still getting PO401
Has any one ever "snaked" or roto-rooter'd their EGR ports? If so how Did you use a chemical agent to assist in the break up of the carbon build up? if so what?

I am somewhat frustrated as I have gotten to the point were I have the whole egr valve and vacuum hoses off in 4 minutes I have done it so many times. Any assistance would be helpfull please

 

[Chevinater77]

i am too frustrated with it! it just came on last week for me after a can of bg44k! I thought that stuff was supposed to be good!
Im gonna try the vsv and clean all the hoses!

Does the code need to be reset or will the light go off when the problem is solved?

 

[NoMoreFires!]

The check engine light will not clear itself on an obd2 vehicle (96 and up) without the problem being fixed for several drive cycles (up to 150 miles each) so I recommend buying a cheap scanner or code reader/clearer and manually clearing the codes. If the problem is still there it may come right back on if it is bad enough or it may not reappear for several drive cycles.

Taken straight from AllData this may help (I doubt the diagrams will appear but the text should be helpful)

DTC P0401 Exhaust Gas Recirculation Flow Insufficient Detected

CIRCUIT DESCRIPTION

The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving conditions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce NOx emissions. The amount of EGR is regulated by the EGR vacuum modulator according to the engine load.
If even one of the following conditions is fulfilled, the VSV is turned ON by a signal from the ECM. This results in atmospheric air acting on the EGR valve, closing the EGR valve and shutting off the exhaust gas (EGR cut-off).
Under the following conditions, EGR is cut to maintain driveability.

• Before the engine is warmed up.
• During deceleration (throttle valve closed).
• Light engine load (amount of intake air very small).
• Engine racing.

DETECTING CONDITION

WIRING DIAGRAM

SYSTEM CHECK DRIVING PATTERN

(1)Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.(2)Start and warm up the engine with all accessories switched OFF.(3)Run the vehicle at 70 ~ 90 km/h (43 ~ 56 mph) for 3 minutes or more.(4)Idle the engine for about 2 minutes.(5)Stop at safe place and turn the ignition switch OFF.(6)Start the engine and do steps (3) and (4) again.(7)Check the "READINESS TESTS" mode on the OBD II scan tool or TOYOTA hand-held tester. If "COMPL" is displayed and the MIL does not light up, the system is normal. If "INCMPL" is displayed and the MIL does not light up, run the vehicle again and check it.
HINT: "INCMPL" is displayed when either condition (a) or (b) exists.

(a)The system check is incomplete.(b)There is a malfunction in the system.
If there is a malfunction in the system, the MIL will light up after steps (2) to (6) above are done.
INSPECTION PROCEDURE

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 8

Step 9

TOYOTA hand-held tester

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7
Step 8
Step 9

OBD II scan tool (excluding TOYOTA hand-held tester)

 

[NoMoreFires!]

Looks like most of the pictures are there, but this is a flow chart to help diagnose p0401

 

[Romer]

Robbie told me this sometimes is fixed by cleaning the throttle body as something gets plugged in there.

 

[Chevinater77]

thanks for the demo, this helps a lot!

 

[jerseyfzj80]

NoMoreFires,

I am wrench i have all of this info as well just looking for the silver bullet, You know the old story the shoemakers children have no shoes, The mechanics landcruiser has PO401 AAHHH. Its just my own laziness

 

[NoMoreFires!]

Just trying to help

 

[jerseyfzj80]

NMF,
I hear wasn't trying to sound ungrateful the frustration is just influencing my mood. I guess that I will just have to bit thebullet and work on the cruiser after I am done working on everyone elses problems @ the end of the day
Dammit this is why I have a toyota so I don't have to do this crap

 

[NoMoreFires!]

Once a year run some type of fuel system cleaner (sea foam type) you will be amazed how much less carbon buildup you will get....make those pricey cats last longer too
(although it will foul the spark plugs sooner)

 

[96r50]

I pulled off my throttle body a few weeks ago to do the cold start mod. With the TB off, you have good access to the EGR tube cast into the intake. I'm surprised my CEL wasn't on more often given the amount of carbon crud I picked out of there (dental picks). It's quite simple to pull the TB and clean the EGR tube (and everything else you can reach). Do it!!

 

[Chevinater77]

cold start mod??? do tell!

 

[jerseyfzj80]

yeah I'm with chevinator Cold start mod?

 

[super90]

If by "the cold start mod" you mean the two o-rings on the shaft of the cold start valve plunger, I did that long ago, and I personally didn't find it worked very well or for very long. Those o-rings got compressed and didn't do what the mod intended.

I had better luck replacing all the vacuum lines, all the intake and plenum seals, getting the injectors cleaned, full tune-up, etc. That lowered my cold start idle.

 

[jerseyfzj80]

Ok pulled the TB, cleaner and more open then I expected, the only thing left is the main ECU or the stupid temp sensor!

 

[gisham]

im going through the same deal on my 94. i replaced the egr, vsv, modulator and all the lines... 2 days later cel was back on- very frusterating, my next move is to pull the bulb and forget it. As to the cold idle, i ended up using washers as the o-rings flattened and cracked. Wroks OK, but still a bit high for my liking. I may replace the idle control valve all together and see what that does. its just money, right?

 

[MoJ]

It's crazy to throw parts at the problem if you haven't thoroughly removed and cleaned the TB. Might as well replace the vac hoses while you're at it, just a few more minutes of work. Cleaning the TB will also help with the high start idle. The o-ring mod never made sense to me. If it didn't roar at start up when it was new why would you mod Mr T's design?

 

[jerseyfzj80]

All hoses have been replaced already and I did clean the TB yesterday, It did Actually pass NJ state inspection last night (NJ onl;y requires 5 monitors be set for a 97 vehicle to pass) had 5 set according to little computer and went right over to inspection and it passed but as soon as I turned it off and then on bingo light came on with you guessed it PO401 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
So I can ignore it for another 2 years or try and finalize this problem once and for all. God i hate this stupid light, Currently the only thing that inspires me to adress this is that there could be some small influence on fuel mileage towards the good side with a proper operating EGR system and since big $ gas is just around the corner I need all the help I can get.

 

[Alex Kogan]

It's crazy to throw parts at the problem

exactly. Never understood that.

if you haven't thoroughly removed and cleaned the TB. Might as well replace the vac hoses while you're at it, just a few more minutes of work. Cleaning the TB will also help with the high start idle. The o-ring mod never made sense to me. If it didn't roar at start up when it was new why would you mod Mr T's design?

Cleaning TB is not going to help much except if by some odd chance two passages atop TB to which tubes from modulator connect are clogged. If it's that bad I would say there are a lot more other problems with this motor unless it has like 300k+ on it.

 

[MoJ]

exactly. Never understood that.

Cleaning TB is not going to help much except if by some odd chance two passages atop TB to which tubes from modulator connect are clogged. If it's that bad I would say there are a lot more other problems with this motor unless it has like 300k+ on it.

Cleaning the TB is easy and nearly free (save for a gasket and TB cleaner). If the ports are blocked to start with you can replace all the components in the system and not get anywhere. Even a well-maintained, relatively low-mile truck will build up gunk in the TB. IMOP it's a matter of base lining the egr system (cleaning the TB and replacing vac hoses) and then following the FSM trouble shooting guide.