Excessive and Insufficient EGR Flow

So this one stumped me. About 3 weeks ago my truck’s check engine light came on. P0402 is the "Exhaust Gas Recirculation Flow Excessive Flow“. I replaced the EGR valve and the light was off for about 500-1000 miles. Then the light popped back on so I tested it again. P0402 as well as P0401, “ Exhaust Gas Recirculation flow insufficient “. They contradict each other so I’m really stumped on this one. Any ideas?

 

Yeah, it's usually not the EGR valve itself that fails on these.
Insufficient or excessive flow is determined by the ECU reading the temp of the EGR gases as they're routed into the intake.
If ECU sees high temps there, it thinks this is from too much hot exhaust gas being run into the intake, and would be the excessive flow code.
Insufficient EGR flow would be determined by the ECU measuring too low of a heat temp, not enough hot EGR gases coming back into the intake.
This is one DTC where it really does help to follow the troubleshooting steps in the FSM.
There is an EGR temp sensor, the EGR modulator, and the EGR vacuum switching valve(vsv). There are steps in the manual that tell you how to test each component to determine which isn't working correctly.
At times, heavy carbon soot crap buildup can plug up the vacuum pathways as well and affect the system

 

@Mart141
I betcha a Nickle it's the VSV and the vac hoses could use a refresh to thick wall silicone.
@cruiserguy is right on with FSM testing but if you're loading the parts cannon save the modulator for last.
Let us know how this works out please.

 

Yeah the testing of modulator was simple too. Like 'put finger over one port and suck through another port, is it clear or plugged? If when port X plugged, if it holds vacuum, its fine....'
Something like that. And the vsv was easy also, like apply vacuum and then 12VDC to connector and see if the other port opens when 12V applied.
I don't have the FSM off hand but the testing worked perfectly for determining the malfunction for me.
On the taco wasn't too bad, but other Yotas I've wrenched on had those vac lines and ports in EGR system chock full of carbon crap. So even if you're vsv was functioning and the modulator as well, it wouldn't matter with the lines plugged.
Only a couple times have I heard of EGR temp sensor falling out of spec.
I think you're order of likeliness of culpability sounds about right

 

@cruiserguy I looked up the factory manual and couldn’t find any EGR troubleshooting solutions. Maybe I’m looking the wrong place? Anything specific I should look up?

 

I can't remember if it's looked up by the DTC(the code itself)?
I'll go grab one of my Land Cruiser FSMs real quick. I forget the format in there. I know Toyota calls them DTCs. Diagnostic troubleshooting codes.

 

Looks like that stuff will be in the 'EG' or 'engine' section.
Pic is only for reference, this is a different year and different vehicle. But is Toyota Factory Service Manual and they all follow similar formats.

 

If you are using the electronic version of the FSM........ May God have mercy on your soul and not allow the suffering to be too excessive

 

@cruiserguy yeah I’ve been looking for an online version since 8:30.... will a Haynes repair manual work? They’re only like $25 at Autozone

 

I dunno, I've never had very good luck with those manuals so I quit even looking at them like 20 years ago when I found out there were actual factory service manuals.
I thought I remember reading some or a thread/s on here that listed the tests for troubleshooting this DTC.
No more links to download the FSM online?

 

No don't do it! Waste of money for the Haynes for anything like this... or anything too specific.. or too much troubleshooting.

Haynes are good for removal and installation of stuff and that's about it.


I only have the electronic version of my FSM and it takes hours to scroll through.. almost bad enough to pay $50 at kinko's to get it printed

 

Update on this form, I’ve worked about 70+ hours in the last week so I haven’t had time to get under the hood. Today I was driving for about 10 minutes and when slowing down my truck sputtered out and turned off. It turned right back on and ran great for about 20 minutes after.... any ideas? Could it be EGR related? Should I stop driving my truck until I fix this problem?

 

Can you link the FSM?

 

This came up on a search of: toyota vacuum modulator p, q, r

http://htftp.offroadsz.com/marinhaker/programi/toyota/Engine/22RE/19egrsy.pdf

My conclusion is it looks like a bad modulator for me, blowing from Q, with P, R plugged is very high resistance. Barely any flow from R (barely audible), more flow from P (louder) but lots of resistance. I already removed the filter and rinsed it, but it didn't clean up much.